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Pd-catalyzed β-carbon elimination of 3-hydroxy-4-pent­enoic acid derivatives promoted by triethylborane proceeds to form conjugated dienes via a decarboxylation process. The formed conjugated dienes undergo the Prins reaction with aldehydes in situ to afford conjugated homoallylic alcohols. These sequential transformations enable the conversion of diastereomeric mixtures of 3-hydroxy-4-pentenoic acids, which are readily prepared from the simple crossed aldol reaction of esters and α,β-unsaturated aldehydes, into 3,5-hexadienyl alcohols with high regio- and stereoselectivities in a single manipulation.

Poly(ester-carbonate) copolymers were synthesized through triethylborane (TEB)-activated, one-pot copolymerization of epoxides with anhydrides (AH) and CO₂. Depending upon the feeding ratio of AH to the epoxides, poly(ester-carbonate) copolymers with random and tapered ester structures could be derived due to the much higher reactivity of AH toward growing oxanions compared to the reactivity of CO₂. Anhydrides like succinic anhydride (SA) and phthalic anhydride (PA) when tried in terpolymerization with epoxides, like propylene oxide (PO) and cyclohexene oxide (CHO), and CO₂ indeed exhibited such high reactivities in comparison to CO₂ that tapered block structures were eventually obtained for high feeding ratios of AH to PO and random copolymers for the AH-to-epoxide feeding ratio lower than 10%. Terpolymerization with different feeding ratios of anhydrides to epoxides was thus systematically investigated. In an alternate path, diblock poly(ester-b-carbonate)s were prepared by sequential copolymerization of epoxide/anhydride and epoxide/CO₂. All of the obtained copolymers were characterized by ¹H nuclear magnetic resonance (NMR), diffusion-ordered spectroscopy (DOSY), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The structures and properties of copolymers obtained by terpolymerizations and block copolymerizations were compared.

The first C5 polymerization is reported, where the main‐chain is growing by five carbon atoms of the monomer at a time. Three dienyltriphenylarsonium ylide monomers were synthesized and polymerized with triethylborane as an initiator, leading to random terpolymers (C1, C3, C5) with mainly C5 repeating units (up to 84.1 %). It has been found that the methyl group (electron‐donating substituent) on the conjugated double bond of the ylides facilitates the formation of C5 segments. A mechanism was proposed based on NMR characterization and DFT calculations. The high C5 content ensures that things are on the right track for pure C5 homopolymerization., Reported for the first time is an unusual borane‐initiated polymerization of arsonium ylide monomers, where the main‐chain grows by five carbon atoms, from the monomer, at a time and leads to unique structures.

The modification of highly oxygenated forskolin as well as manoyl and epi-manoyl oxide, two less functionalized model substrates sharing the same polycyclic skeleton, via intermolecular carbon-centered radical addition to the vinyl moiety has been investigated. Highly regio- and reasonably stereoselective iodine atom transfer radical addition (ATRA) reactions were developed. Unprotected forskolin afforded an unexpected cyclic ether derivative. Protection of the 1,3-diol as an acetonide led the formation of the iodine ATRA product. Interestingly, by changing the mode of initiation of the radical process, in situ protection of the forskolin 1,3-diol moiety as a cyclic boronic ester took place during the iodine ATRA process without disruption of the radical chain process. This very mild radical-mediated in situ protection of 1,3-diol is expected to be of interest for a broad range of radical and non-radical transformations. Finally, by using our recently developed tert-butyl­catechol-mediated hydroalkylation procedure, highly efficient preparation of forskolin derivatives bearing an extra ester or sulfone group was achieved.

Biomass-derived 5-chloromethylfurfural (CMF), a congener of the well-known carbohydrate-based platform chemical 5-hydroxymethylfurfural (HMF), can efficiently be functionalised by radical transformations of its benzylic chloromethyl group. We report here the first examples of these radical reactions by way of metal-free, triethylborane/oxygen-induced atom transfer radical addition (ATRA) reactions between CMF and styrenes, which proceed with high yield and selectivity. The key intermediate, the 2-formyl-5-furfuryl radical derived from CMF, and its radical addition reactions were studied with regard to its electronic structure, i.e. spin density distribution and frontier molecular orbitals based on the NBO ansatz and activation barriers of the addition step using DFT and post-HF methods.

The activation and deactivation of the chain-transfer agent were achieved by oxygen initiation and regulation with triethylborane under ambient temperature and atmosphere. The autoxidation of triethylborane overcame the oxygen inhibition and produced initiating radicals that selectively activate the chain-transfer agent for the chain growth or deactivate the active chain-end of polymer in controlled radical polymerization. Both activation and deactivation were highly efficient with broad scope for various polymers with different chain-transfer agents in both organic and aqueous systems. Oxygen molecule was particularly used as an external regulator to initiate and achieve the temporal control of both activation and deactivation by simply feeding the air.

A key challenge in polymer chemistry is to regulate the polymer sequence and architecture from versatile monomer mixtures. Here we describe the triethylborane/1,8-diazabicyclo[5.4.0]undec-7-ene (Et3B/DBU) pair catalysed highly selective terpolymerization of mixtures of propylene oxide (PO), phthalic anhydride (PA) and racemic lactide (rac-LA), wherein the catalytic efficiency and the polymerization selectivity are significantly correlated to the Et3B/DBU feed ratio. With H2O as a cheap and efficient initiator, the Et3B/DBU pair (1/1) demonstrates chemoselective control over the ring-opening copolymerization (ROCOP) of PO/PA and the ring-opening polymerization (ROP) of rac-LA, while the Et3B/DBU pair (2/1) additionally allows for the discrimination of rac-LA and PO in ROP via kinetic control, affording one-step access to unique AzCy(AB)xCyAz pentablock terpolymers (Đ < 1.15) without transesterification scrambling.

In this paper, the DFT methods were applied at the M06-2X/6–311++G(d,p) levels of theory to investigate the β-hydrogen elimination in the (C2X5)2B(C2H5); X=H, F, Cl, Br. It was attempted to show how the electronegativity of halogen affects the barrier height (ΔE‡) and thermodynamic parameters (ΔG‡ and ΔH‡) of this reaction. The Wiberg bond indices were employed to check the progress of the reactions. The synchronicity values of the reactions were determined as well. The kinetic parameters of these reactions were computed in 300-1200 K temperature range. Furthermore, the fitted equations to the gas phase Arrhenius equation were found. Effect of the electronegativity of halogen was exemplified on the kinetic parameters.

Pd-catalyzed regio- and enantioselective allylic etherification of vinylethylene carbonates (VECs) with diols has been developed. By using cooperative catalysts of the chiral palladium complex and triethylborane in mild conditions, the process gave monoetherified and bisetherified polyglycol derivatives with tetrasubstituted stereocenters in high yields with complete regioselectivities and high levels of enantio- and diastereoselectivities.

A general method for the hydroalkylation of electron-rich terminal and non-terminal alkenes such as enol esters, alkenyl sulfides, enol ethers, silyl enol ethers, enamides and enecarbamates has been developed. The reactions are carried out at room temperature under air initiation in the presence of triethylborane acting as a chain transfer reagent and 4-tert-butylcatechol (TBC) as a source of hydrogen atom. The efficacy of the reaction is best explained by very favorable polar effects supporting the chain process and minimizing undesired polar reactions. The stereoselective hydroalkylation of chiral N-(alk-1-en-1-yl)oxazolidin-2-ones takes place with good to excellent diastereocontrol., Giese reaction not anymore limited to electron poor alkenes! A general method for the radical mediated hydroalkylation of electron rich alkenes including enol ethers, silylenolethers, enamides, and enecarbamates has been developed.

Phthalic anhydride and propylene/ethylene oxide are copolymerized at room temperature by a bicomponent metal-free catalyst comprising a mild phosphazene base and triethylborane. Provided with proper loadings of the two catalytic components, block copolymers with strict (AB)

Synthesis of high molecular weight alternating copolymers from epoxides and norbornene anhydride via metal-free catalyst remains a challenge in aliphatic biodegradable polyester synthesis. Metal-free Lewis pair catalyst system, consisting of Lewis acid B(C2H5)3 (triethylborane) and a Lewis base DMAP (4-dimethylaminopyridine); TBD (1, 5, 7-triazabicyclo[4.4.0]dec-5-ene) and DBU (1,8 diazabicyclo[5.4.0]undec-7-ene) as a cooperative catalyst system for fully alternating polyesters synthesis is described here. By using these simple systems we have obtained, high molecular weight (Mn = 2–31.5 kDa) polyesters with narrow molecular weight distributions (MWD’s = 1.948–1.069) via ring-opening alternating copolymerisation (ROAC) of various epoxides (e.g. CHO, cyclohexene oxide; PO, propylene oxide; tBGE, tert-butyl glycidyl ether and PGE, phenyl glycidyl ether) with cis-5 norbornene-endo 2, 3 dicarboxylic anhydride (NB). Furthermore, we demonstrated that these polyesters are biocompatible in nature when tested on human embryonic kidney cells (HEK-293) showing more than 80% cell viability in 72 h and can be used for different biological applications such as drug delivery, tissue engineering or anti-microbial polymeric coatings on biomedical devices. The use of these green functional polyesters for biological studies was realized for the first time by a metal-free Lewis pair approach.

Reported herein is the development of a simple but practical catalytic system for the selective reduction of amides with hydrosilane or hydrosiloxane. Low-cost and readily available triethylborane (1.0 M in THF), in combination with a catalytic amount of an alkali metal base, was found to catalyze the reduction of all three amide classes (tertiary, secondary, and primary amides) to form amines under mild conditions. In addition, the selective transformation of secondary amides to aldimines and primary amides to nitriles can also be achieved by using a proper combination of BEt3 and base. The scope of these BEt3-base-catalyzed amide hydrosilylation reactions has been explored in depth. Preliminary results of mechanistic studies suggest a modified Piers' silane Si-H···B activation mode wherein the hydride abstraction by BEt3 is promoted by the coordination of an alkoxide or hydroxide anion to the Si center.

Tetrabutylammonium carbonate (TBAC) which is obtained by treating CO2 with tetrabutylammonium hydroxide is shown to perform as an ideal difunctional initiator for the copolymerization of carbon dioxide (CO2) and propylene oxide (PO) in the presence of triethylborane (TEB). In this system, CO2 thus serves as the initiating moiety of its own copolymerization with epoxides when used in the form of a carbonate salt. Based on this remarkable result, mono-, tri-, and tetrafunctional ammonium carboxylate initiators and also other difunctional carboxylate initiators were synthesized and used for the synthesis of well-defined ω-hydroxyl-polycarbonates with linear and star structures. Well-defined telechelics, three- and four-armed star samples of molar mass varying from 1 kg/mol to 10 kg/mol, with around 95% carbonate content, were successfully synthesized. The structure of the obtained polycarbonate ω-polyols were characterized by 1H NMR, MALDI-TOF, and GPC. The terminal hydroxyl functionality of polycarbonate di...

An efficient method for the construction of arylated allylic ethers was developed via three-component tandem arylation and allylic etherification of 2,3-allenol with aryl iodides and alcohols. In the cooperative catalytic system of a palladium complex and triethylborane, the process allows rapid access to functionalized 1-arylvinylated 1,2-diol derivatives in good to high yields with complete branch-selectivities. The synthetic utility of the present process was demonstrated by the late-stage functionalization of a drug molecule, the gram-scale synthesis and the elaboration of the products.

Various oxirane monomers including alkyl ether or allyl-substituted ones such as 1-butene oxide, 1-hexene oxide, 1-octene oxide, butyl glycidyl ether, allyl glycidyl ether, and 2-ethylhexyl glycidyl ether were anionically copolymerized with CO2 into polycarbonates using onium salts as initiator in the presence of triethylborane. All copolymerizations exhibited a "living" character, and the monomer consumption was monitored by in situ Fourier-transform infrared spectroscopy. The various polycarbonate samples obtained were characterized by H-1 NMR, GPC, and differential scanning calorimetry. In a second step, all-polycarbonate triblock copolymers demonstrating elastomeric behavior were obtained in one pot by sequential copolymerization of CO2 with two different epoxides, using a difunctional initiator. 1-Octene oxide was first copolymerized with CO2 to form the central soft poly(octene carbonate) block which was flanked by two external rigid poly(cyclohexene carbonate) blocks obtained through subsequent copolymerization of cyclohexene oxide with CO2. Upon varying the ratio of 1-octene oxide to cyclohexene oxide and their respective ratios to the initiator, three all-polycarbonate triblock samples were prepared with molar masses of about 350 kg/mol and 22, 26, and 29 mol % hard block content, respectively. The resulting triblock copolymers were analyzed using H-1 NMR, GPC, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy. All three samples demonstrated typical elastomeric behavior characterized by a high elongation at break and ultimate tensile strength in the same range as those of other natural and synthetic rubbers, in particular those used in applications such as tissue engineering.

In this investigation, a metal-free process was developed that enables the synthesis of poly(propylene carbonate) (PPC) diols/polyols by copolymerization of CO2 with propylene epoxide (PO) under environmentally friendly and cost-effective conditions. This process implies the recycling of triethylborane and of ammonium salts that both enter in the composition of the initiators used to copolymerize CO2 and PO. In complement to the above approach, a polymeric support, poly(diallyl dimethylammonium chloride), was synthesized and modified to carry ammonium carboxylate salts along its chain. The prepared polymeric initiator was utilized to copolymerize CO2 with PO under heterogeneous conditions. Not only were the polymerization results similar to the samples obtained under homogeneous conditions, but the polymer substrate could easily be recovered by simple filtration. The integrity of the polycarbonate diols/polyols and the recycling process were followed by 1 H and 11 B NMR spectroscopy, gel permeation chromatography, and matrix assisted laser desorption ionization time of flight (MALDI-TOF) MS.

The heats of combustion at 25 °C of trimethylborane (liquid), triethylborane (liquid), and tri-n-butylborane (liquid), to form crystalline boric acid, liquid water, and gaseous carbon dioxide have been determined to be −2989.4 ±22.4 kj/mole (−714.48 ±5.36 kcal/mole), −4975.6 ±15.1 kj/mole (−1189.2 ±3.6 kcal/mole), and −8901.0 ±10.2 kj/mole (−2127.4 ±2.4 kcal/mole), respectively. These data, combined with the heats of formation of boric acid, carbon dioxide, and water give −34.79 ±5.40, −47.2 ±3.7, and −83.2 ±2.5 kcal/mole at 25 °C for the standard heats of formation of trimethylborane, triethylborane, and tri-n-butylborane, respectively. The data of other investigators are discussed briefly.

International audience; Propylene oxide (PO) is polymerized by metal-free ring-opening 11 polymerization (ROP) at 25 °C using N-heterocyclic carbenes (NHCs) and 12 triethylborane (Et 3 B) as a bicomponent catalytic system. Poly(propylene oxide)s with 13 predictable molar mass up to 60 000 g.mol-1 and low dispersity (Ð < 1.10) were 14 obtained without the occurrence of undesirable transfer reaction to the monomer. In 15 presence of an alcohol as the initiator, the ROP of PO follows an anionic mechanism 16 assisted by monomer activation improving the efficiency of NHCs for the 17 polymerization of substituted epoxides. Et 3 B is involved both in the formation of a 18 complexed active center and in the activation of PO. Interestingly, 19 dihydroxytelechelic PPOs can be readily synthesized not only using 1,4-20 benzenedimethanol but also water, both serving as difunctional initiators. Block

Ring-opening polymerization (ROP) is a versatile approach to well-defined polymers. Achieving both high efficiency and precise control remains a major challenge. We herein report room-temperature living ROP of epoxides catalyzed by combined organobase and triethylborane (Et3B) with water or alcohols as initiators. Extremely high catalytic efficiency (turnover frequency up to 6000 h–1) is exhibited despite the relatively mild Lewis basicity and acidity, and the catalyst loading can be minimized to 44 ppm. Poly(ethylene oxide) products are noncytotoxic toward a variety of cell lines even without purification. Poly(propylene oxide) with molar mass as high as 210 kg mol–1 and low dispersity (ĐM < 1.1) can be achieved owing to the absence of detrimental transfer reactions. The chemoselectivity allows the catalyst to be readily applied to living ROP of glycidyl ethers, tailored synthesis of diverse functional/block/nonlinear (co)polyether structures, and one-pot one-catalyst synthesis of polyether-based polyure...

A series of aggregation-induced emission (AIE) active core crosslinked miktoarm star copolymers, having multi polyethylene (PE) and poly(methacrylic acid) (PMAA) arms, were synthesized and their thermal/pH responsive properties were studied. The procedure involves (a) the synthesis of PE-Br by polyhomologation of dimethylsulfoxonium methylide with triethylborane as initiator, followed by oxidation-hydrolysis/esterification reactions and of poly(tert-butyl methacrylate) (PtBMA-Br) by atom transfer radical polymerization (ATRP) of tert-butyl methacrylate, (b) the synthesis of (PE)n-(PtBMA)m-P(TPE-2St) by ATRP of a double styrene-functionalized tetraphenylethene (TPE-2St) with PE-Br and PtBMA-Br macroinitiators, and (c) the hydrolysis of (PE)n-(PtBMA)m-P(TPE-2St) to afford the amphiphilic miktoarm star copolymers (PE)n-(PMMA)m-P(TPE-2St). Due to their spherical core–shell structure (temperature-responsive) and the presence of hydrophilic PMAA (pH-responsive) and TPE-2St (AIE), these miktoarm star copolymers ...

A rapid oxygen-initiated and -regulated controlled radical polymerization was conducted under ambient temperature and atmosphere. The reaction between triethylborane and oxygen provides ethyl radicals, which initiate and mediate the radical polymerization. The controlled radical polymerization was achieved using RAFT chain transfer agents (CTA) without any process of removing oxygen, providing well-defined polymers with almost full conversion (>95 %) in a short period (15 min). High-throughput screening was used to discover the suitable conditions for various CTA and monomers. To show the versatility of this method, a polymer library containing 25 well-defined polymers with different compositions (block and statistical copolymers) and molecular weights were synthesized in 1 h via high-throughput synthesis technique. A polymer-painting technique was developed using this method, forming films with spatial control and excellent control in molecular weight and dispersity.

The C≡C bonds of various alkynylgermanes [Cl(H)Ge(C≡C–R1)2, Cl2Ge(C≡C–R1)2 with R1 = nBu, SiMe3, and Ge(C≡C–R1)4 with R1 = SiMe3] undergo 1,1-carboboration when treated with an excess of triethylborane at 80–110 °C. All pure final products with R1 = SiMe3 possess germole-derived structures. Intermediates and side products as a result of lost stereoselectivity of the 1,1-carboborations could be detected and in some cases identified by NMR spectroscopic studies of the reaction solutions.

A radical "on water" addition to the C═N bond of hydrazones has been described. Hydrazone, diphenylsilane, alkyl iodide, and triethylborane afforded the corresponding addition products "on water" in good yields. A significant solvent effect was observed from the water. The developed protocol can be applied to the synthesis of 3-substituted isoindolinone derivatives. Moreover, the process offers environmentally benign tin-free radical reaction conditions.

Selective incorporation of deuterium atoms into molecules is of high interest for labeling purposes and for optimizing properties of drug candidates. A mild and environmentally benign method for the deuteration of alkyl iodides via radical pathway using D2O as source of deuterium has been developed. The reaction is initiated and mediated by triethylborane in the presence of dodecanethiol as a catalyst. This method is compatible with a wide range of functional groups and provides the monodeuterated products in good yields and with a high level of deuterium incorporation. It opens promising opportunities for the development of enantioselective radical reactions. Moreover, a revision of the mechanism of the deoxygenation reaction of xanthates using R3B and water (Wood deoxygenation) is presented.

Copolymerization of butyl acrylate with a large excess of boiling vinyl butyl ether was carried out in the presence of triethylborane. The analysis of the composition of the obtained product demonstrated that an alternating low-molecular-weight copolymer was predominantly formed. The formation of macromolecules occurred by both conventional and controlled radical polymerization (CRP), as evidenced by a bimodal molecular weight distribution. As conversion increased, the mode corresponding to the CRP mechanism shifted toward larger molecular masses. The relative activities of comonomers for the process initiated by triethylborane were calculated.

2-Fluoro-1,3-dienes were synthesized through nickel-catalyzed coupling reactions between β,β-difluorostyrenes and alkynes in the presence of ZrF4 as co-catalyst and a hydride source derived from triethylborane and lithium isopropoxide. Mechanistic studies revealed that the carbon–fluorine bond was cleaved by β-fluorine elimination from intermediary nickelacyclopentenes generated through oxidative cyclization of the two substrates.

Aggregation-induced emission (AIE) active core cross-linked multiarm star polymers, carrying polystyrene (PS), polyethylene (PE), or polyethylene-b-polycaprolactone (PE-b-PCL) arms, have been synthesized through an “arm-first” strategy, by atom transfer radical copolymerization (ATRP) of a double styrene-functionalized tetraphenylethene (TPE-2St) used as a cross-linker with linear arm precursors possessing terminal ATRP initiating moieties. Polyethylene macroinitiator (PE–Br) was prepared via the polyhomologation of dimethylsulfoxonium methylide with triethylborane followed by oxidation/hydrolysis and esterification of the produced PE–OH with 2-bromoisobutyryl bromide; polyethylene-block-poly(e-caprolactone) diblock macroinitiator was derived by combining polyhomologation with ring-opening polymerization (ROP). All synthesized star polymers showed AIE-behavior either in solution or in bulk. At high concentration in good solvents (e.g., THF, or toluene) they exhibited low photoluminescence (PL) intensity d...

An autocatalytic cycle was found in the mechanism of autoxidation of triethylborane using density functional theory calculations. The reaction starts with the generation of an ethyl radical via slow homolytic substitution. Fast radical propagation then takes place through a catalytic cycle in which the ethyl radical acts as a catalyst.

Et3B/O2-mediated radical coupling reactions of O,Te-acetal 2 were explored using diverse electrophilic double bonds. Ethyl radical derived from Et3B under air cleaved the C–Te bond of 2 to generate α-alkoxy bridgehead radical I, which reacted with cycloalkenones, cycloalkylidenemalononitriles, allyl halides, and imines at or below ambient temperature. These intermolecular reactions from O,Te-acetal 2 were mild and versatile, and were superior to those of O,Se-acetal 1 in terms of efficiency and substrate scope. A total of 14 new and nine improved coupling reactions are described, all of which realized the installation of the functionalized carbon units at the sterically hindered bridgehead position of trioxaadamantane.

A concise route for the preparation of two simple optically pure indolizidin-5-ones has been developed. The key chain elongation process was achieved using a triethylborane/catechol mediated hydroalkylation of Boc-protected 2-vinylpyrrolidines. By using complementary strategies, these two bicyclic lactams can be alkylated with complete control of the stereochemistry at C(5) and their conversion to a variety of indolizidine alkaloids such as coniceine, indolizidine 209D and 167B, 5-epi-indolizidine 249A and monomorine has been reported in the literature.

Here, we describe a novel [3 + 2] cycloaddition of 3-substituted indoles with vinyl aziridines and vinyl epoxides that provides a straightforward approach to pyrroloindolines and furoindolines bearing vinyl groups (up to 96% yield and 9:1 dr). In contrary to previous reports involving Lewis acid activation, this work reports successful reactions based on the activation of indole using t-BuOK and BEt3 (triethylborane), thereby preserving the free N–H group on indoles. In addition, a gram-scale reaction and a ring-closing metatheis reaction are performed to provide good demonstrations of the synthetic utility of this approach.

A novel approach to prepare the core structure of Aspidosperma and Strychnos alkaloids is described. The strategy is based on a cyclization cascade involving the formation of quaternary carbon center followed by trapping of the radical intermediate by an aryl azide to build the 5-membered ring of the pyrrolocarbazole system. This reaction is run with triethylborane without the need for any hydrogen atom donor such as a tin hydride or tris(trimethylsilyl)silane, and it furnishes the tetracyclic framework as a single diastereomer. The influence of different N-protecting groups on the starting iodoacetamide has been examined.

2-Amino-6-chloropyrimidin-4(3 H )-one (6-chloroisocytosine) reacted with methyl-, vinyl-, phenyl-, and benzylimidazole, respectively, to give isocytosinate-imidazolium salts which were deprotonated with an anion exchange resin to yield the corresponding cross-conjugated mesomeric betaines (imidazolium-isocytosinates). The vinyl derivative, however, polymerized under these conditions. The betaines are in equilibrium with their N -heterocyclic carbenes, isocytosine-imidazol-2-ylidenes. Results of DFT calculations reveal that the betaine tautomer is the most stable tautomer in polar solvents, whereas the carbene is more stable in vacuo. Trapping reactions of the carbene tautomers, including the vinyl derivative, were performed with sulfur and selenium which resulted in the formation of the corresponding thiones and selenones, respectively. The in situ generation of the betaine/carbene tautomers in the presence of triethylborane in a Schlenk tube at elevated temperatures and pressures gave novel zwitterionic 8-amino-10,10-diethyl-6-oxo-6,10-dihydro-1 H -imidazo[2′,1′:3,4][1,4,2]diaza-borolo[1,5-c]pyrimidin-4-ium-10-ides, in which the boron atom bears the negative charge whereas the positive charge is delocalized in the imidazolium ring. This ring system is a formal trapping product of the carbene as well as the betaine tautomer.

A direct method for white phosphorus functionalization by hydride sources is presented. Excess BH4(-) in n-butylamine produces HP4(-) as the major P-containing species. Reaction with LiBEt3H forms the borane-stabilized phosphanide Li(PH2)(BEt3)2, which may be used to synthesize various phosphines. Triethylborane may be replaced by BH3, resulting in the formation of LiPH2(BH3)2.

Nickel(0)-catalyzed coupling reactions of 1,6- and 1,7-enals with triethylsilane have been utilized to synthesize six- and seven-membered silyl-protected benzocycloalkanols. When triethylborane was employed as the reducing reagent, tetralol derivatives were obtained. Results of deuterium-labeling experiments suggest the formation of oxanickelacycles as a key reaction intermediate.

Compensatory (or compensation) copolymerization of alkyl (meth)acrylates (AMA) with boiling vinyl butyl ether (VBE), initiated by the system of triethylborane (TEB)–oxygen, has been studied. The obtained data indicate a partial formation of copolymer macromolecules with close to an alternating structure, according to the reversible inhibition mechanism, along with a copolymer formation on the scheme of conventional bimolecular termination. Specific features of used acrylic monomers have been revealed. Copolymers of methyl methacrylate (MMA) and VBE were applied as macroinitiators for block-copolymer syntheses when adding new portions of butyl acrylate (BA).

6-Chloropurine and 2,6-dichloropurine were reacted with N1-substituted imidazoles to give purin-6-yl substituted imidazolium salts, respectively. Deprotonation of the 1-methylimidazolium derivative resulted in the formation of the corresponding stable conjugated mesomeric betaine, whereas the 1-phenyl,- 1-vinyl- and 1-(2-hydroxyethyl) derivatives proved to be unstable. In situ generation of the mesomeric betaines by caesium carbonate in the presence of sulfur and selenium, however, gave the thiones and the selenones of the tautomeric purine-substituted imidazol-2-ylidene, respectively. Its anionic N-heterocyclic carbene was formally trapped by reaction with triethylborane at high temperatures as a cyclic boron adduct which is the first representative of a new heterocyclic ring system. DFT calculations gained insight into the electronic properties of the N-heterocyclic carbenes substituted by π-electron donators. Results of a single crystal X-ray analysis of the boron adduct are presented.

Treatment of N-Boc-2-aryl-1,2,3,4-tetrahydroquinolines with n-butyllithium in THF at −78 °C resulted in efficient lithiation at the 2-position and the organolithiums were trapped with a variety of electrophiles to give substituted products. Variable temperature NMR spectroscopy gave kinetic data that showed that the rate of tert-butoxycarbonyl (Boc) rotation was fast (ΔG‡ ≈ 45 kJ mol−1 at −78 °C) and in situ ReactIR spectroscopy showed fast lithiation at −78 °C. By carrying out the lithiation in the presence of the chiral ligand sparteine, kinetic resolutions with very high levels of enantioselectivity were achieved. The resulting enantioenriched N-Boc-2-aryltetrahydroquinolines were converted to 2,2-disubstituted products without significant loss in enantiopurity. Most electrophiles add at the 2-position and the chemistry provides a way to access tetrahydroquinolines that are fully substituted alpha to the nitrogen atom. Notably, either enantiomer of the 2,2-disubstituted tetrahydroquinolines can be obtained with high selectivity from the same enantiomer of the chiral ligand. Unusually, when methyl cyanoformate was used as the electrophile, substitution occurred in the ortho position of the aryl ring attached at C-2. This change in regioselectivity on changing the electrophile was probed by deuterium isotope studies and by DFT calculations which suggested that the binding of the cyanoformate altered the structure of the intermediate organolithium. Secondary amine products can be prepared by removing the Boc group with acid or by inducing the Boc group to rearrange to the 2-position in the presence of triethylborane and this carbonyl N-to-C rearrangement occurs with retention of configuration from the intermediate enantiomerically enriched organolithium species.

Two versions of the free-radical thiol–ene addition, a photoinduced reaction in the presence of 2,2-dimethoxy-2-phenylacetophenone, and a UV-light-free hydrothiolation using triethylborane as the initiator, were studied for the conjugation of fluorescent dithiomaleimide to biologically active compounds. A dithiomaleimide derivative bearing a vinyl ether functionality was prepared as the alkene partner. This was coupled with a range of thiols, including thiosugars, captopril, N-acetyl-L-cysteine, and sodium 2-sulfonatoethanethiol. The Et3B-initiated method was superior to the photoinduced reaction, as it minimized decomposition of the sensitive maleimide group. The vinyl ether derivative and the addition products showed green light emission in tetrahydrofuran. The compounds all showed almost identical absorption and emission spectra, proving that the structure of the thiols has no influence on the fluorescence properties of the maleimide part of the molecules. The hydrothiolation products showed relatively high quantum yields.

In this account, our studies on radical reactions that are promoted by dimethylzinc and air are described. Advantages of this reagent and differences from conventional radical initiators, such as triethylborane, are discussed., Article first published online: 17 JUL 2015

The combination of a Pd catalyst and triethylborane promotes double amphiphilic allylation of nitriles with 2-methylenepropane-1,3-diol to serve as a 1,3-dipolar equivalent, providing pyrrolizidine derivatives. The resulting bicyclic compounds can be used for efficient synthesis of important pyrrolizidine alkaloids.

A method for direct synthesis of tetrasubstituted fluoroarenes via nickel-catalyzed [2+2+2] cycloaddition is presented. The reaction combines one molecule of 1,1-difluoroethylene with two molecules of alkynes and involves sequential cleavage of the C-F and C-H bonds in difluoroethylene. The catalytic cycle is established by reduction of the intermediary Ni(II) fluoride with a triethylborane-based borate.

A reaction of N-tosyl cycloalkanecarbaldimines with iodomethyl pivalate was initiated by triethylborane to give pivaloyloxymethylated products bearing 3-iodocycloalkyl groups. Radical addition of pivaloyloxymethyl to imines generates aminyl radicals, which then regioselectively cleave C H bonds at the 3-position of the cycloalkane moieties. The resulting carbon-centered radicals are trapped with iodine. DFT calculations rationalized stereo- and regioselectivity.

Triethylborane (TEB) was found to be a mild, efficient, and acid catalyst in electrophilic substitution reaction of indoles with aldehydes compounds to afford the corresponding bis(indolyl)methanes. Vibrindole A (5) and bis(indolyl)methanes derivatives 16 and 18 were synthesized using this methodology. Compound 16 is an intermediary in the synthesis of the natural bisindoles arsindoline B (2) and streptindole (6). The structure of vibrindole A (5) was unequivocally confirmed by a single crystal X-ray diffraction analysis.

A total synthesis of Daphnodorin A, a member of the Daphnodorins, was accomplished. Key features of the synthetic strategy include construction of 2-substituted-3-functionalized benzofuran via intramolecular Heck reaction and a mild Barton–McCombie deoxygenation process mediated by triethylborane. The total synthesis provided Daphnodorin A in 19.7% or 5.6% overall yield over 7 or 15 steps.

An efficient radical (2-pyridylsulfonyl)difluoromethylation of terminal alkenes with 2-PySO2CF2I has been successfully achieved by using catalytic amount of Et3B/air as initiating system. This methodology was also further extended to the synthesis of 2-PySO2CF2-substituted alkanes and alkenes.

The two-stage method for poly(methyl acrylate) grafting starch using triethylborane and 1,4-benzoquinone has been developed. The first stage was borylation of alcohol groups of starch. The second stage was polymerization of methyl acrylate in the inhibitor - 1,4-benzoquinone - presence accompanied by the S H 2-substitution at the boron atom. The advantages of developed method were the homogeneity of the process, the high yield of graft-copolymer, the possibility to control of chain length of synthetic polymer, and the absence of homopolymer in the final product. The molecular weight characteristics of starch-graft-poly(methyl acrylate) copolymer was determined by gel-permeation chromatography. The evidence of the graft-copolymer formation was 11B nuclear magnetic resonance data and its glass-transition temperature. The resulting graft-copolymer has an amphiphilic nature and a high thermal stability compared to the corresponding homopolymers (starch and poly(methyl acrylate)). According to the calculated values of the surface Gibbs energy the surface of starch-graft-poly(methyl acrylate) films is characterized as a high-energy surface.