Search

Fluorenones (III) are synthesized through intramolecular carbonylative C—H/C—I coupling of 2-iodobiphenyls (I) using furfural (II) as a carbonyl source and the combination of [RhCl(cod)]2 and DPPP as catalyst.

Paraformaldehyde serves as a carbonyl source in the Pd-catalyzed cyclocarbonylation of 2-bromobiphenyls through the cleavage of a C–H bond to afford good yields of fluoren-9-one derivatives. This p...

This paper reports nitrosoallene-mediated synthesis of α-substituted enoximes. Nucleophilic substitution of nitrosoallenes, a novel chemical species prepared from allenyl N-hydroxysulfonamides, afforded α-functionalized enoximes. Introduction of various nucleophiles proceeded smoothly to form C–N, C–O, C–S, C–F, and C–C bonds in the presence of azodicarboxylates.

Both the decarbonylative degradation of formaldehyde (II) to a CO moiety and hydrogen and the subsequent hydroformylation of vinylarenes are promoted by a chiral single-loaded Rh(I)-catalyst.

The synthesis of cyclopenta[c]furanones (III) and cyclopenta[c]pyrrolones (V) by the title reaction is accomplished by simultaneous use of neutral and cationic rhodium(I) complexes for efficient cooperative catalysis, which involves neutral rhodium(I)-catalyzed decarbonylation of formaldehyde (II) and cationic rhodium(I)-catalyzed cyclocarbonylation of 1,6-enynes [(I) and (IV)] with the free carbonyl moiety.

Some results indicate that the reaction proceeds through methylenetriazolium intermediates.

Total synthesis of α,β-, and α,β,γ,δ-unsaturated imine ant venom alkaloids is described. The labile two conjugated imine alkaloids were synthesized by late stage intramolecular Schmidt reaction via allyl and pentadienyl cation intermediates.

The rhodium(I)-catalyzed reaction of alkynes with arylboronic acids in the presence of formaldehyde resulted in a carbon monoxide gas-free carbonylative arylation to yield α,β-enones. The simultaneous loading of phosphine-ligated and phosphine-free rhodium(I) complexes is required for efficient catalysis, which catalyze the abstraction of a carbonyl moiety from formaldehyde (decarbonylation) and its subsequent introduction into the substrate (carbonylation), respectively.

An increased enantiomeric excess of 21% could be achieved by the selective excitation of a chiral substrate-template supramolecular complex.

Regioselective rapid triazole syntheses at low temperature are described. Organic azides and propargyl cations generated by acids gave fully substituted 1H-1,2,3-triazoles. Most reactions could be performed in 5 min at not only rt but also −90 °C. Both terminal and internal alkynes were acceptable, and the sterically bulky substituents could afford the products smoothly. Various types of three-component coupling reactions were demonstrated, and the presence of allenylaminodiazonium intermediates was indicated.

An enhancement of conversion is observed for the title reaction around the critical density of CO2 due to a clustering effect.

A novel photolabile protecting group, thiochromone S,S-dioxide, possessing the 1,2-diol group for protection of ketones and aldehydes is described. Photodeprotection of the successfully protected carbonyl derivatives proceeded smoothly under photoirradiation filtered through Pyrex glass (>280 nm) using an ultrahigh-pressure mercury lamp to recover the corresponding carbonyl compounds and the starting protecting group.

An efficient synthesis of α,β-unsaturated alkylimines at low temperature using azides has been developed. Carbocations generated from allyl alcohols helped achieve a rapid conversion under mild conditions with azides to afford reactive α,β-unsaturated imines. Hydroxy or alkoxy groups are essential for these transformations, and utilizing readily accessible allyl alcohols gave a wide extension of substrates. The efficiency of this novel method is demonstrated in the total synthesis of an iminium ant venom alkaloid.

Double nucleophilic N-alkylation of α-oxime-esters, affording N , N -dialkyl-α-amino acids is herein described. Grignard reagents accomplished double N-alkylations via umpolung and various N , N -dialkylated α-amino acids were successfully synthesized in 15 min. Both electron-withdrawing sulfonyl groups and electron-donating silyl and methyl groups on oximes were available. Alkylmagnesium species and ( E )-configuration of α-oxime-ester were essential to this cascade reaction.

The new, efficient, and stereoselective method to prepare biologically important 3-arylated isoindolinones can also be applied to synthesize enantioenriched 3-arylphthalides.

Optically active glyceraldehyde acetonide (II) is employed for the Rh-catalyzed cyclocarbonylation of various enynes to produce bicyclic cyclopentenone derivatives.

Formation of hetarenoindanone (II) from 2-methyl thiochromone derivative (I) follows a cascade reaction sequence involving an intramolecular Friedel—Crafts reaction and subsequent oxidation by selenous acid which is generated from selenium dioxide and water through Riley allylic oxidation.

The reaction of enynes with acetyl-masked aldoses in the presence of a rhodium(I) catalyst resulted in cyclocarbonylation, thus avoiding the direct use of carbon monoxide, to afford bicyclic cyclopentenones. In rhodium catalysis, aldoses serve as a carbon monoxide equivalent by donating their carbonyl moieties on the acyclic aldehyde form to enynes. A variety of aldoses, including d-glucose, d-mannose, d-galactose, d-xylose, and d-ribose, can be used as a carbonyl source. Using the method, a wide variety of enynes were cyclocarbonylated in 22−67% yields. An asymmetric variant also proceeded with moderate to high enantioselectivity.

The cyclocarbonylation of 1,6- and 1,7-yne–imines leading to bicyclic α,β-unsaturated lactams can be achieved in the presence of a catalytic amount of Ru3(CO)12. The reaction, a [2+2+1] cycloaddition, incorporates the acetylene π-bond, the imine π-bond, and the carbon atom of CO. The presence of substituents, such as alkyl, aryl, and silyl on the acetylenic terminal carbon is essential for yne–imines to undergo cyclocarbonylation to give bicyclic α,β-unsaturated lactams. An yne–imine having no substituents on the acetylenic terminal carbon does not give the corresponding lactam, but rather a dihydropyridine derivative without incorporating CO.

Reaction of cyclic γ-cyanoketones with 3 equiv. of SmI2 in the presence of t-BuOH as a proton source in HMPA–THF without photoirradiation gave the desired α-hydroxycycloalkanones along with overreduced ketones after hydrolysis. In the absence of t-BuOH, the formation of the overreduced ketones was depressed and the yields of the α-hydroxyketones increased, while the reaction proceeded slowly.

The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)](2)/dppp results in the Pauson-Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation.

The skeletal reorganization of 1,6- and 1,7-enynes leading to 1-vinylcycloalkenes using Rh(II) as a catalyst is reported. Two possible isomers of 1-vinylcycloalkenes, type I and type II, can be obtained, the ratio of which are highly dependent on the substitution pattern of the enynes used. Formation of type I compounds involves a single cleavage of a C-C double bond, the product of which is identical to that of enyne metathesis. In contrast, the formation of type II compounds involves the double cleavage of both the C-C double and triple bonds, which has an anomalous bond connection. The presence of both a phenyl group at the alkyne carbon and a methyl group at the internal alkene carbon facilitates the formation of type II compounds. The electronic and steric nature of the substituents on the aromatic ring also affects the ratio of type I and type II. The nature of a tether also has a significant effect on the course of the reaction. Experimental evidence for the intermediacy of a cyclopropyl rhodium carbenoid, a key intermediate in the skeletal reorganization of enynes, is also reported. In addition to the skeletal reorganization of enynes, Rh(II) complexes were found to have a high catalytic activity for some cycloisomerization reactions of alkyne derivatives, including the bicyclization of enynes to bicyclo[4.1.0]heptene derivatives and the cyclization of alkynylfurans to phenol derivatives.

Compared to enantioselective Friedel–Crafts reactions of indoles, reactions of alkylidene malonates with monocyclic aromatic compounds generally proceed with low enantioselectivity. The Friedel–Crafts reactions of ethenetricarboxylates 1 and monocyclic heteroaromatic compounds, such as substituted pyrroles and furans were investigated. The reaction of 1 with 2,4-dimethylpyrrole in the presence of a chiral bisoxazoline–copper(II) complex (10 mol %) in tetrahydrofuran at room temperature gave alkylated products in up to 72% ee. The reaction of 1 with 2-substituted furans gave alkylated products in 46–62% ee. The absolute stereochemistry of the furan Friedel–Crafts product 7e was determined by transformation to the known 2,3-dimethylbutyric acid. The intramolecular reaction of benzene derivatives gave cyclized products up to 56% ee.

Zinc Lewis acid-catalyzed cyclization of ethenetricarboxylate derivatives 1 with 2-ethynylanilines has been examined. Reaction of 1,1-diethyl 2-tert-butyl ethenetricarboxylate 1b with 2-(trimethylsilylethynyl)aniline substrates in the presence of Zn(OTf)2 gave bridged quinoline derivatives in 43−85% yield. The reaction of 1b with 2′-aminoacetophenone also gave the bridged quinoline derivative in 41% yield. Thermal reaction of bridged quinolines (180−190 °C) afforded indole derivatives in moderate to good yields.

The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)]2 and [RhCl(cod)]2 were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the α-position of indenones.

One-pot, four-step syntheses of indoles using both solid-supported heterogeneous and homogeneous palladium catalysts and reagents were carried out. Such a combination of these two-phase catalysts and reagents causes a dramatic increase in yield, and it is a simple process. The presented methodology is effective for four-step reactions to provide various functionalized indoles.

A new protocol for CO gas-free carbonylation, in which aldehydes are used as a substitute for CO, is described. The protocol consists of two Rh-mediated processes; the Rh-mediated decarbonylation of aldehydes, which leads to the formation of Rh carbonyl, and subsequent Rh-catalyzed carbonylative cyclization utilizing the in situ formed Rh carbonyl species.

3-Arylthiochromone derivatives were synthesized as new photolabile protecting groups, in which the photoreactivity was switchable based on oxidation of the sulfur atom (sulfide and sulfone); the protected substrates 9,14 released the corresponding alcohols, amines or carbonxylic acids almost quantitatively under UV-light in neutral condition and the photoproduct 10 showed high fluorescence intensity.

Oxygen-containing heterocyclic systems are important structures in organic chemistry because of their presence in many biologically active compounds. In this work, a Lewis acid-catalyzed cyclization of ethenetricarboxylate derivatives 1 with substituted propargyl alcohols to give methylenetetrahydrofurans was investigated. Reaction of 1 and γ-silicon-substituted propargyl alcohols 4 with ZnBr2 at 80−110 °C led to (Z)-silicon-substituted products stereoselectively. Reaction of 1 and γ-ester-substituted propargyl alcohol 7 in the presence of various Lewis acids gave ester-substituted methylenetetrahydrofurans stereoselectively. Interesting Lewis acid dependency on stereoselectivity for the reaction of 7 was found. Reaction of α-substituted propargyl alcohols also gave cyclized products.

The first example of an aqueous, asymmetric, and CO gas-free Pauson–Khand-type reaction is described. Using formaldehyde as a commercially available substitute for carbon monoxide, combined use of a hydrophilic phosphine (TPPTS) and a hydrophobic, chiral phosphine (tolBINAP) enable the reaction to proceed smoothly in aqueous media, even in the absence of carbon monoxide, and stereoselectively.

The reaction of N-Ts-(2-bromophenyl)alkylamines with aldehydes in the presence of a catalytic amount of a rhodium complex results in the intramolecular aminocarbonylation of the aryl halides to give five-, six-, and seven-membered benzolactams.

Radical ring-opening reactions of bicyclo[4.2.0]octanones, its C6 alkyl derivatives, and tricyclic ketones promoted by SmI2 gave cyclohexanones via fission of the external cyclobutane bond. The CO2Me, CN, and phenyl derivatives led to the production of the eight-membered ring compounds through cleavage of the central cyclobutane bond. Using this regioselective reaction, the synthesis of (±)-acorenone was achieved.