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The dual role of nitrogen bases is shown in the ARGET ATRP with ascorbic acid acetonide. High pKa bases lead to more ascorbate anion (faster polymerizations) but in presence of oxygen/water are detrimental to the catalyst (hydroxide formation).

An anomalous polystyrene gel was obtained during the copper-catalyzed “activators regenerated by electron transfer” “atom transfer radical polymerization” (ARGET ATRP) of styrene at 60–70 °C, using ascorbic acid/Na2CO3 as the reducing system and EtOAc/EtOH as the solvent mixture. The result is remarkable since no branching nor cross-linking reagents were added to the reaction mixture and their formation in situ was excluded. The anomalous PS branching, at the origin of the phenomenon, requires a generic bifunctional initiator and is mechanistically bound to termination reactions between bifunctional macroinitiators. As a matter of fact, the branching/cross-linking phenomenon loses intensity, or even disappears, under reaction conditions that cause the built-up of CuII or increase the chain polymerization rate. The temperature is also a critical variable since no branching was observed for temperatures higher than 90 °C. We believe that the route toward gelation starts with a controlled chain polymerization of styrene from the bifunctional initiator, soon integrated by a step-growth polymerization due to radical coupling of the terminal units. The progressive decrease in the number of chains and free radicals in the reaction mixture should make more and more probable the intramolecular coupling between the C−Cl ends of the remaining long and entangled chains, producing a polycatenane network. [Figure not available: see fulltext.]

“Activator regenerated by electron transfer” “atom transfer radical polymerization” (ARGET ATRP) process catalyzed by CuCl2/tris(2-pyridylmethyl)amine (TPMA) (1/1) in ethyl acetate/ethanol (EtOAc/EtOH) for the polymerization of styrene from ethyl 2,2-dichloropropanoate (EDCP) is described. The (re)generation of the activating CuI complex is accomplished by Na2CO3 without the addition of any explicit reducing agent. Differently from the analogous process operating in the presence of ascorbic acid/carbonate as the reducing system, branching is not present and control over polymerization is improved. The activation mechanism should follow a composite route, where both EtOH and TPMA contribute to the regeneration of the catalyst. The oxidation of TPMA is suggested by the absence of the ligand in the final reaction mixture and by the reduction of CuII even in t-BuOAc/t-BuOH, notwithstanding the very poor ability of t-BuOH as a reducing agent. Oxidative degradation of TPMA causes a progressive malfunctioning of the redox catalyst. Consequently, the polymerization rate, after a prompt start, becomes slower and slower, fixing conversions at around 50% (4.5 h). This means a gradual decrease of the free radical concentration, which develops unfavorable conditions for the reductive coupling (termination) between the bifunctional growing chains, preserving a controlled growth of the polymer.

A new copper(II) chloride/tris(2-piridylmethyl)amine (1/1) catalysed “Activators Regenerated by Electron Transfer” “Atom Transfer Radical Polymerisation” (ARGET ATRP) process for the polymerisation of styrene is described. The salient features of the method are the simultaneous use of ascorbic acid (reducing agent) and Na2CO3 (basic agent), the employment of a bifunctional initiator (ethyl 2,2-dichloropropionate) and the utilisation of a green solvent mixture composed of ethyl acetate and ethanol (AcOEt/EtOH). Na2CO3 plays a central role since not only preserves the ligand from protonation, but it can also activate the reducing agent. The quantity of monomer in the reaction mixture, the AcOEt/EtOH ratio and the load of ascorbic acid/carbonate are important factors for achieving a regular transformation. Working at 100 °C and with a metal load of only 0.025 mol%, an almost perfectly controlled telechelic polystyrene is produced, provided that conversion is kept below 50%. If conversion is higher, the control is gradually lost due superimposition of a step-growth process to the main chain polymerisation process. Two interesting phenomena, encountered during this study, are activation of the redox complex by using only Na2CO3 and gelation of polystyrene at 60 °C.

Atom transfer radical polymerization (ATRP) is one of the most powerful techniques to synthesize precisely tailored polymers and macrostructures. Activators regenerated by electron transfer (ARGET) ATRP was developed as a “green” strategy to decrease the load of the metal catalyst. However, ARGET ATRP usually uses not-so-green reducing agents (e.g. Sn2+) or expensive and industrially impractical procedures. For these reasons, we report an ARGET ATRP of styrene with various carbonates as reducing agents, both alone and paired with ascorbic acid (AA), using monofunctional initiators and Cl or Br as exchanging atoms. The solvent mixture is composed of the green combination of EtOAc and EtOH, even in the presence of modest amounts of H2O. Cyclic voltammetry was used to evaluate the effect of H2O on the catalyst, as well as the absence of AA. The system returned high yields and low dispersities with low amounts of catalyst (~60 ppm) and moderate reaction times. Excellent results were obtained only with the Cl-ATRP system. NMR spectroscopy and kinetic analyses proved the livingness of the final polymer chains.

The barrier to rotation around the N-alkenyl bond of 38 N-alkenyl-N-alkylacetamide derivatives was measured (ΔG⧧ rotation varied between 20 kcal mol–1) were studied to determine the regiochemistry of cyclization. Those with high barriers (>27 kcal mol–1) did not lead to cyclization, but those with lower values produced highly functionalized γ-lactams via a 5-endo-trig radical–polar crossover process that was terminated by reduction, an unusual cyclopropanation sequence, or trapping with H2O, depending upon the reaction conditions. Because elevated temperatures were necessary for cyclization, this precluded study of the asymmetric transfer in the reaction of individual atropisomers. However, enantiomerically enriched atropsiomeric enamides should be regarded as potential asymmetric building blocks for reactions that can be accomplished at room temperature.\ud \ud

The kinetics of the ring-into-ring conversion of some new (Z)-phenylhydrazones of 3-benzoyl-1,2,4-oxadiazole containing different nitrogen-substituents at C-5 (3b–d; X = NHMe, NMe2, and NHCOMe) into the relevant triazoles 4b–d have been examined in a wide range of pS+ (0.1–11.9) in 1:1 (v/v) dioxane/water solution. The obtained results have been compared with previous data concerning the (Z)-phenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole (3a; X = NH2). All of the studied (Z)-phenylhydrazones rearrange through three different pathways (specific acid-catalysed, uncatalysed and general base-catalysed). The different effects of the substituents on the course of the rearrangement in the three pathways have been examined.

The N-arylsulfonyl group, which is the best and most useful cyclization auxiliary for the transition-metal-catalyzed atom transfer radical cyclization (ATRC) of N-allyl-α-polychloroamides, can be effectively removed from the target γ-lactams by using H2SO4–HOAc, without impairing the halogen functions. The reaction involves H+ attack on the aromatic moiety, and is strongly responsive to the electronic properties of the substituent bound to the aromatic ring: electron-donating groups, such as methyl or methoxy are, in fact, required for efficient “deprotection”. The N-p-nitrophenylsulfonyl cyclization auxiliary, in contrast to all the other sulfonyl groups tested, proved to be unsuitable for the ATRC, owing to a side reductive transposition that halts the redox cycle.

The unusual migration of a nitro group from the - to the -position of a -aryl--nitroethenyl moiety, following a nitrocyclopropane to isoxazoline N-oxide isomerization, has been studied from a mechanistic and synthetic points of view. As a result, two series of isomeric isoxazoline N-oxides could be obtained under controlled conditions. When reacted with diazomethane, a model transposed isoxazoline cleanly furnished a new, interesting pyrazolylisoxazole.

The cyclisation of N-allyl-N-substituteda- polychloroamides is efficiently obtained through a copper-catalysed activators regenerated by electron transfer–atom transfer radical cyclisation process, with a metal load of only 0.5 mol%. The redox catalyst is introduced in its inactive form as copper( II) chloride/[nitrogen ligand] complex, and continuously regenerated to the active copper(I) chloride/[ nitrogen ligand] species by ascorbic acid. To preserve the catalyst integrity, the hydrochloric acid, released after each regeneration cycle, has been quenched by carbonate. The choice of the solvent is critical, the best performance being observed in ethyl acetate-ethanol (3:1).

Copper mediated cyclization of activated 1-substituted enamides occurs via a 5-endo radical-polar crossover process. Trichloroacetyl derivatives can undergo further reactions post cyclization (elimination of HCl or dimerization potentially via copper carbenoid intermediates). Reaction of α-halo trienamides derived from β-ionone furnish either β- or γ-lactams via 4-exo or 5-exo cyclizations respectively depending upon the enamide tautomer undergoing reaction. For the less reactive dichloroacetamide derivative a competing regioselective methyl migration-aromatization prior to cyclization is observed.\ud \ud

Recently we found that a copper catalysed Ueno–Stork cyclization can be a very useful means for the expedient synthesis of dichloro-γ-lactones, but, to take advantage of this step, the method still lacks of an efficient and selective follow-up. This Letter describes our progress in that field, unveiling the use of a supported and recyclable Cr (VI) catalyst for the simultaneous deprotection and oxidation of cyclic dichloro hemiacetals.

The distinctive nucleus of kainoid amino acids, (2S,3R)-(+)-2-carboxypyrrolidine-3-acetic acid 6, was synthesized by a chemoenzymatic process, exploiting the diastereomeric cis/trans methyl pyroglutamate derivatives 10a, 10b, 10c/11a, 11b, 11c as key intermediates. These mixtures, when subjected to a kinetic resolution mediated by α-chymotrypsin, reacted diastereo-, regio-, and enantioselectively to give the trans derivatives (+)-10a, 10b, 10c possessing the correct (2S,3R) configuration. Subsequently, the desired product (2S,3R)-(+)-6 could be obtained after well-established transformations. Chirality, 2012. © 2011 Wiley Periodicals, Inc.

The selective and efficient acetylation of the hemiacetal hydroxyl in the equilibrium mixture between RCl2C(OAll)OH and AllOH/RCl2CHO was achieved using the acylating system Ac2O/Et3N/dimethylaminopyridine (DMAP).

Esterase from Horse Liver (HLAP) was able to hydrolyze a series of linear and cyclic β,β-dialkyl-γ-nitroesters, in spite of the well-known reluctance of hydrolytic enzymes to recognize and transform hindered substrates, such as those possessing a stereogenic quaternary carbon atom next to the reaction site. The resulting optically active γ-nitroesters gave access to optically active β,β-disubstituted γ-aminoacids as well as α,α-disubstituted succinic acids, both being biologically relevant compounds.

3-Alkyl-3-chloro-4-chloromethyl-γ-lactones were synthesized in acceptable yields, exploiting the CuCl-N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyzed atom transfer radical cyclization (ATRC) of O-allyl-2,2-dichlorohemiacetal acetates, starting materials easily prepared from 2,2-dichloroaldehydes. The oxidation of the intermediate dichloro-2-acetoxytetrahydrofurans was completed in a two-step, one-pot procedure: hydrolysis to γ-lactol and final oxidation to lactone with Jones' reagent.

An unreported 5-endo-trig atom-transfer radical cyclization of cyclic N-α-dichloroacyl-ketene-N,S-acetals, which evolves as a tandem radical-polar process, is described. The reaction, which is carried out in the presence of a Cu(I) complex catalyst (10 mol%) and an inorganic base (i.e., carbonate), can be exploited as the key step for a novel, short, and versatile synthesis of the 3,4-disubstituted maleic anhydride nucleus.

The synthesis of tyromycin A and that of the non-natural lower homologue, involving as featuring steps a transition metal catalyzed atom transfer radical cyclization and a functional rearrangement of the polyhalogenated 2-pyrrolidinones thus obtained, are described. Both routes use 10-undecenoic acid, a renewable source from castor oil, as starting material for the preparation of the pivotal intermediates α,α,α′,α′-tetrachlorodicarboxylic acids.

A new, five-step route to ( Z)-pulchellalactam, a CD45 protein tyrosine phosphatase inhibitor, is presented. Key steps are the copper(I) chloride-bipyridyl catalyzed atom-transfer radical cyclization- of an appropriate allyl α,α-dichloroacetate and the subsequent dehydrochlorination/prototropic rearrangement of the resulting dichlorolactone.

The natural fragrances (+)- trans whisky lactone 2 and (+)- trans cognac lactone 4 , together with a minor amount of their (−)- cis stereoisomers, were prepared in 50% and 42% overall yield, respectively, starting from racemic 1-hepten-3-ol (±)- 5 and 1-octen-3-ol (±)- 6 . The procedure involved first the enantioconvergent, lipase mediated transformation of the secondary allylic alcohols derived dichloroacetates (±)- 7 and (±)- 8 into the corresponding homochiral (+)- 7 and (+)- 8 , combined with their cyclization under a transition metal catalyzed atom transfer process.

Transition metal-catalyzed atom transfer radical cyclization of N-tosyl-N-allyl-α-polychloroamides produces N-tosylated γ-lactams, which can be highly efficiently N-deprotected by thermolysis in a 1:1 mixtures of 96% H2SO4 and acetic acid.

The rearrangement of eight new Z -arylhydrazones of 3-benzoyl-5-phenylisoxazoles ( 3d – k ) into the relevant 2-aryl-4-phenacyl-2 H -1,2,3-triazoles ( 4d – k ) in dioxane/water solution at different proton concentrations has been quantitatively studied in a wide temperature range (293–333 K). The data collected together with some our previous ones on compounds 3a – c have allowed a deep study of the substituent effects on the course of the rearrangement, thus increasing our knowledge on the Boulton–Katritzky reactions in isoxazole derivatives and on the temperature effects on free energy relationships.

The rearrangement of a trichloro-pyrrolidin-2-one, prepared by the CuCl–TMEDA catalyzed atom transfer radical cyclization of N-alkyl-N-(3-chloro-2-propenyl)-2,2-dichloromyristamide, with n-propylamine or CH3ONa/CH3OH, is the key step of a new, short and inexpensive route to chaetomellic anhydride C and (±)-erythro-roccellic acid.

The reaction of 4-methyl-pyrrolidin-2-ones, chlorinated at the C(3) and C(6) positions, with n-propylamine constitutes a new method for the preparation of 5-propylimino-pyrrolidin-2-ones or 3-pyrrolin-2-ones in generally good yields. The transformation involves a series of eliminations, substitutions and double bond shifts. This constitutes a remarkable example of a functional rearrangement.

The copper(I) or ruthenium(II)-mediated radical cyclisation of halo-amides has been utilised to afford functionalised pyrrolidinones via 5-endo-trig or 5-exo-trig radical cyclisation pathways. This methodology has been applied to novel and concise syntheses of the anti-epileptic drug gabapentin and the biologically active natural product pulchellalactam.

α,β-Unsaturated hydrazones can be easily converted into N -allyl hydrazines by reaction with dimethylamine–borane/ p -toluenesulfonic acid under mild reaction conditions. The reduction works well for N ′-allylhydrazides but N ′-allyl- N , N -dimethylhydrazines are rapidly reoxidised by air and so need to be manipulated under an inert atmosphere prior to N ′-acylation. Competitive conjugate reduction can also be observed and the regioselectivity of the dimethylamine–borane attack is determined by steric and/or electronic factors. The procedure is also effective for the CN reduction of unconjugated hydrazones.

The efficiency of the Boc-protecting group in the cyclization of O-allyl dichloroacetals to lactols and subsequent hydrolysis/oxidation to functionalized γ-lactones (III)/(IV) is demonstrated.

The intramolecular Diels−Alder reaction of N-allyl-N-(2-furylmethyl)amides to exo-N-acyl-3-aza-10-oxatricyclo[5.2.1.01,5]dec-8-enes is described. The cycloaddition is controlled not only by the size of the amide appendage, but also by electronegativity of the amide. An example of a new approach towards the synthesis of a highly functionalized pyrrolizidine ring, which links this Diels−Alder cycloaddition to an halogen atom transfer radical cyclization, is reported.

Cyclisation of a variety of halo-enamides with copper(I) or ruthenium(II) complexes has been investigated. The regioselectivity of the radical cyclisation, which can proceed via either a 4- exo or 5- endo pathway, to form β- or γ-lactam products respectively, is determined by the nature of the metal oxidant and the reaction conditions. Thus, whereas copper(I)/bipyridine reactions give predominantly γ-lactams, the use of copper(I)/TMEDA or dichlorotris(triphenylphosphine)ruthenium(II) affords mainly β-lactams.

An effective and environmentally benign preparation of 2,2-dichloroaldehydes has been achieved by chlorination of aldehydes with Cl 2 (g) in CH 2 Cl 2 , using 2,6-lutidine hydrochloride as recoverable catalyst. Remarkable qualities of the process are: easy work up, high purity products, HCl as the only ‘waste’ stream and inherent bias to the scale up.

The rearrangement of γ-chlm, β-hydroxy or β-vmyl N-allyl-N-benzyl-α,α-dichlorocarboxyamides to γ-aminobutynic acid analogues is efficiently promoted by CuCI\N,N,N′,N′-tetramethylethylendiamine. With the β-vinyl functionalization a tandem radical-radical reaction, yieldmg 3-aza-2-oxo-bicyclo[3,3,0]actatre adducts, is also observed.

Monodispersed telechelic oligomers have been efficiently prepared by Fe0−FeCl3 promoted halogen atom transfer radical of functional telogens and taxogens.

Oxidation of β-hydroxy thioethers with MnO2-aqu. 35%/HCl in methanol gives β-hydroxy sulfoxides in high yields.

A new practical route to chaetomellic acid A (ACA), based on the copper catalysed radical cyclization (RC) of (Z)-3-(2,2-dichloropropanoyl)-2-pentadecylidene-1,3-thiazinane, is described. Remarkably, the process entailed: (i) a one-pot preparation of the intermediate N-alpha-perchloroacyl-2-(Z)-alkyliden-1,3-thia-zinanes starting from N-(3-hydroxypropyl)palmitamide, (ii) a two step smooth transformation of the RC products into ACA and (iii) only one intermediate chromatographic purification step. The method offers a versatile approach to the preparation of ACA analogues, through the synthesis of an intermediate maleic anhydride with a vinylic group at the end of the aliphatic tail, a function that can be transformed through a thiol-ene coupling. Serendipitously, the disodium salt of 2-(9-(butylthio)nonyl)-3-methylmaleic acid, that we prepared as a representative sulfurated ACA analogue, was a more competent FTase inhibitor than ACA. This behaviour was analysed by a molecular docking study. (C) 2012 Elsevier Ltd. All rights reserved.

Methyl 2,2-dihalocarboxylates add easily to carbonyl compounds in fair to good yields through the intermediate formation of 2-haloester enolates; the reaction is promoted by zinc, following a “Barbier” type procedure.

The chemoselective N-acylation of 2-amino alcohols with methyl 2,2-dichloro carboxylates occurs smoothly and in excellent yields.

Methyl 2-Br-2-Cl-carboxylates afford 2-alkyl-2-Cl-4-Br-carboxylates in fair yields by reaction with terminal alkenes, under mild conditions, through a radical process promoted by CuBr/Fe0 in DMF/CH2C12.

N-alkyl-2,2-dihaloamides were efficiently prepared by amino-de-alkoxylation of methyl 2,2-dihalocarboxylates, at room temperature without solvents and promoters. Excellent yields of anilides were obtained after addition of AlCl 3 .

α-Acetoxy acid methyl esters are prepared in excellent yields by treating aliphatic α-acetoxy dimethyl acetals with trichloroisocyanuric acid in DMF.

(Z)-Alkyl α-Cl-α,β-unsaturated esters are prepared in excellent yields by stereoselective dehydrobromination of alkyl α-Br-α-Cl-carboxylates with LiClLi2CO3 in dimethylformamide.

Thirty-four @2-R1C2R2)Co2(C0)6 complexes (14 new) were prepared and characterized by their IR v(C0) and lH- and 13C-NMR spectra. The 13C-NMR chemical shifts of the coordinated sp carbon atoms were correlated with those of the corresponding free acetylenes. This indicated that the interaction between the R1 and R2 groups and the c2co2(co)6 moiety is very sensitive not only to the donor/acceptor character of R1 and R2 but also to the orbital symmetry of the atoms attached directly to the C(sp) atoms. The changes of the W3C) values of the C(sp) atoms upon coordination were also analyzed in these terms. It is concluded that although the dinuclear p2-coordination of the acetylene results in a high degree of excitation the stability of the c2co2(co)6 moiety diminished the reactivity of the organic ligand. Differences in the reactivity of the @2-R1C2R2)Co2(CO)6 complexes in carbonylation are also discussed. The crystal and molecular structure of (PhC2SiPhs)Coz(CO)a was determined by single crystal X-ray diffraction. This compound crystallizes in the orthorhombic Pbca space group with a = 28.790(2) A, b = 11.577(1) A, c = 17.833(2) A, 2 = 8. The structure was determined with R = 0.039, R, = 0.036.

The presented hexa-atomic cyclic ketene-N,S-acetals show the best results in the title reaction compared with penta-atomic cyclic ketene-N,S-acetals and hexa-atomic cyclic ketene-N,N-acetals.

The discovery that cycloalkanes can form thermomorphic systems with typical polar organic solvents has led to the development of less-polar electrolyte solutions. Their mixing and separation can be regulated reversibly at a moderate temperature range. The phase switching temperature can be controlled by changing the solvent compositions. While biphasic conditions are maintained below the phase switching temperature, conductive monophasic conditions as less-polar electrolyte solutions are obtained above the phase switching temperature. After the electrochemical transformations, biphasic conditions are reconstructed below the phase switching temperature, facilitating the separation of cycloalkane where hydrophobic products or designed hydrophobic platforms are selectively partitioned. Several polar organic solvents, including acetonitrile, methanol, and pyridine, can be used in this system according to the requirement of the reactions.

The preparation of -perchloroacyl chlorides, from reaction of the corresponding unfunctionalized acyl halides with chlorine, was efficiently achieved under base-catalysis, using a tetraalkylammonium chloride as catalyst. The process is solvent-free and the procedure is easy, inexpensive, and suitable for scale-up.

CuBr-LiOCH3 in methanol efficiently promotes the reductive coupling of methyl α-bromo-α-chlorocarboxylates to dimethyl α,α′-dichloro-succinates.

Treatment of thioethers with manganese(IV)oxide-35% aqueous hydrogen chloride in methanol gives sulfoxides in high yields; sulfones are not produced

Methyl 2,2-dichloro or 2-bromo-2-chloro carboxylates were obtained in excellent yields by oxidation–chlorination of 2-(1-haloalkyl)-4-methyl-1,3-dioxolanes with trichloroisocyanuric acid.