Concerted catalytic reactions for conversion of ketones or enol acetates to chiral acetates

[reaction: see text] Enol acetates or ketones asymmetrically transformed to chiral acetates in high yields with high optical purities through multistep reactions catalyzed by a lipase and a ruthenium complex. 2,6-Dimethylheptan-4-ol was chosen as a suitable hydrogen donor, and 4-chlorophenyl acetate was used as an acyl donor for the conversion of ketones.     

Highly enantioselective hydrogenation of enol acetates catalyzed by Ru-TunaPhos complexes

[reaction: see text] The chiral disphosphines with tunable dihedral angles (TunaPhos) have been used for asymmetric hydrogenation of enol acetates and dihedral-angle-dependent enantioselectivities were observed. C2-TunaPhos has been proved to be effective for Ru-catalyzed asymmetric hydrogenation of electron-deficient and other enol acetates.     

Catalytic enantioselective fluorination of α-cyano acetates catalyzed by chiral palladium complexes

The catalytic enantioselective electrophilic fluorination promoted chiral palladium complexes is described. Treatment of α-cyano acetates with N-fluorobenzenesulfonimide as the fluorine source under mild reaction conditions afforded the corresponding α-cyano α-fluoro acetates in high yields with excellent enantiomeric excesses (85-99% ee).     

High enantioselectivity in rhodium-catalyzed allylic alkylation of 1-substituted 2-propenyl acetates

[reaction: see text] Rhodium-catalyzed asymmetric allylic alkylation of 1-substituted 2-propenyl acetates with dimethyl malonate proceeded with high enantioselectivity in the presence of cesium carbonate as a base and a rhodium catalyst generated from Rh(dpm)(C(2)H(4))(2) (dpm = dipivaloylmethanato) and a chiral phosphino-oxazoline whose basic skeleton is axially chiral binaphthyl to give branch alkylation products in greater than 90% ee.     

Phosphine-catalyzed regiospecific allylic amination and dynamic kinetic resolution of Morita-Baylis-Hillman acetates

Exposure of Morita-Baylis-Hillman (MBH) acetates to tertiary phosphine catalysts in the presence of 4,5-dichlorophthalimide enables regiospecific allylic substitution through a tandem S(N)2'-S(N)2' mechanism. Through the use of the chiral phosphine catalyst (R)-Cl-MeO-BIPHEP, chiral racemic MBH acetate 4 is converted to the corresponding allylic amination product in 80% yield and 56% enantiomeric excess, thus establishing the feasibility of dynamic kinetic resolution. [reaction: see text]     

Novel functionalized trisubstituted allylboronates via Hosomi-Miyaura borylation of functionalized allyl acetates

[reaction: see text] A series of novel functionalized achiral and chiral allylboronates have been synthesized via the nucleophilic addition of boronates on allyl acetates derived via vinylalumination or Baylis-Hillman reaction of aldehydes. These reagents, upon allylboration with aldehydes, furnish beta-substituted-alpha-methylene-gamma-butyrolactones stereoselectively.     

Stereocontrolled palladium-catalysed umpolung allylation of aldehydes with allyl acetates

In the present work the stereocontrolled palladium-catalysed umpolung allylation of aldehydes is described. Allyl acetates are in situ transformed into the corresponding allyl boronates, which directly react with aldehydes. The question of stereocontrol is raised by employing (a) chiral boronating agents (reagent control) and by (b) utilising chiral aldehydes (substrate control). These studies reveal that the approach based on substrate control is superior to the former one with respect to yields and stereoselectivity. Remarkably, this umpolung protocol often yields the 4,5-syn products in high selectivity, which is unprecedented for direct crotylations.     

Copper-catalyzed asymmetric propargylic amination of propargylic acetates with amines using BICMAP

The copper-catalyzed asymmetric propargylic amination of propargylic acetates 1 with amines 2 using BICMAP as a chiral ligand gave the desired products 3 in good yields and with moderate to high enantioselectivities (up to 90% ee).     

Catalytic enantioselective synthesis of glutamic acid derivatives via tandem conjugate addition-elimination of activated allylic acetates under chiral PTC conditions

A new, general, and practical procedure for the asymmetric synthesis of 4-alkylidenyl glutamic acid derivatives via a catalytic enantioselective tandem conjugate addition-elimination on allylic acetates under chiral phase-transfer conditions is reported. A variety of structural types of allylic acetates have been reacted with the benzophenone imine of glycine tert-butyl ester to give the products in good to excellent yields and enantioselectivities (63-92% yield, 80-97% ee, 8 cases).     

Chiral phosphine-catalyzed regio- and enantioselective allylic amination of Morita–Baylis–Hillman acetates

Enantioselective allylic substitution of Morita–Baylis–Hillman (MBH) acetates with phthalimide was realized in the presence of a novel l-proline-derived chiral trifunctional phosphine amide ligand to give the corresponding allylic amination adducts in good yields (70–95%) and in modest to good enantioselectivities (34–78% ee’s).     

Chemoenzymatic dynamic kinetic resolution of allylic alcohols: a highly enantioselective route to acyloin acetates

Dynamic kinetic resolution (DKR) of a series of sterically hindered allylic alcohols has been conducted with Candida antarctica lipase B (CALB) and ruthenium catalyst 1. The optically pure allylic acetates obtained were subjected to oxidative cleavage to give the corresponding acylated acyloins in high yields without loss of chiral information.     

Chiral bifunctional organocatalysts in asymmetric aza-Morita-Baylis-Hillman reactions of ethyl (arylimino)acetates with methyl vinyl ketone and ethyl vinyl ketone

The bifunctional chiral phosphine Lewis base (R)-2'-diphenylphosphino-[1,1'-binaphthalene]-2-ol is an effective organocatalyst in the asymmetric aza-MBH reaction of ethyl (arylimino)acetates 1 with MVK and EVK to give the corresponding adducts in moderate to good yields and good to high enantiomeric excesses under mild conditions.     

Alkyl 2-(2-benzothiazolylsulfinyl)acetates as useful synthetic reagents for alkyl 4-hydroxyalk-2-enoates by sulfinyl-Knoevenagel reaction

Isopropyl, ethyl, and methyl 2-(2-benzothiazolylsulfinyl)acetates have been found to be useful synthetic reagents for sulfinyl-Knoevenagel reaction with various aldehydes to give directly the corresponding 4-hydroxyalk-2-enoates [R′CH(OH)CHCHCO₂R], which are ubiquitous structures in biologically active natural products and useful building blocks for organic synthesis of chiral compounds. From the optically pure (R)-2-(2-benzothiazolylsulfinyl)acetates (>99% ee) prepared by the enzymatic kinetic resolution of (±)-2-(2-benzothiazolylsulfinyl)acetates, optically active 4-hydroxyalk-2-enoates (up to 91% ee) have been obtained in good yields.     

Palladium-catalyzed deracemization of allylic carbonates in water with formation of allylic alcohols: hydrogen carbonate ion as nucleophile in the palladium-catalyzed allylic substitution and kinetic resolution

The palladium-catalyzed deracemization of racemic cyclic and acyclic allylic methyl carbonates in water in the presence of N,N'-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphophino)benzamide] proceeds with high enantioselectivities to give the corresponding allylic alcohols in high yields. This deracemization involves a palladium-catalyzed allylic substitution with the in-situ-formed hydrogen carbonate ion and an irreversible decomposition of the intermediate allylic hydrogen carbonates, with formation of the corresponding allylic alcohols. The palladium-catalyzed reaction of racemic cyclic allylic acetates with potassium hydrogen carbonate in water in the presence of the chiral bisphosphane proceeds with a highly selective kinetic resolution to give the corresponding allylic alcohols and allylic acetates.     

Synthesis and PMR spectra of 7-hydroxyalkylguanosinium acetates

Guanosine and 9-methylguanine treated with epoxides in glacial acetic acid are hydroxyalkylated stereoselectively at the N₇ position of the guanine moiety. Previously unreported 7-(hydroxyalkyl)guanosinium acetates from the reactions of six epoxides with guanosine and 7-(hydroxyalkyl)-9-methylguaninium acetates from the reactions of two epoxides with 9-methyl guanine in glacial acetic acid have been prepared and characterized by their pmr spectra. By using an excess of epoxide, quantitative conversion of guanosine or 9-methylguanine to the corresponding 7-hydroxyalkylguanosinium or 7-hydroxyalkyl-9-methylguaninium acetate was achieved. Comparisons of the pmr spectra of the 7-(hydroxyalkyl)guanosinium acetates in DMSO-d₆ to the spectrum of guanosine reveal that the H₈ and amino group proton absorptions common to guanosine are shifted to a lower field, the absorptions of the H₁ proton is absent, and the coupling constant of the H′₁-H′₂ protons of the ribosyl group is decreased from about 5.7 ± 0.1 Hz in guanosine to about 3.5 ± 0.1 Hz in the products. The use of the pmr spectral features of 7-(hydroxyalkyl)-9-methylguaninium compounds in characterizing 7-hydroxyalkylguanosinium compounds is discussed. Evidence is presented which suggests that extensive delocalization of positive charge exists in both the pyrimidine and imidazole rings of N₇-hydroxyalkylated guanosine and N₇-hydroxyalkylated-9-methylguanine. The possible effects of charge delocalization upon the hydrogen bonding potential of 7-hydroxyalkylated guanine moieties in DNA is discussed.     

Palladium-catalysed synthesis of allyl acetates from allenes

Allyl acetates were synthesised from allenes utilising methodology based on the general reactivity of π-allyl palladium intermediates which participate efficiently in transformations involving nucleophiles. Reactions of allenes and aryl iodides in the presence of AcONa and Pd(OAc)₂/PPh₃ as the catalytic system afforded allyl acetates in moderate to good yields. Monosubstituted allenes, depending on their structure, produced either a separable mixture of two regioisomeric products or a single regioisomer. As allylic acetates can be easily hydrolysed, the methodology is applicable for the synthesis of allyl alcohols as well.     

Features of complexing of molecular NMR relaxation probes with cellulose acetates in solutions

The method of active and inert NMR relaxation probes can be used for determining the degree of substitution of cellulose acetates. The formation of hydrogen bonds between the hydroxyl and acetate groups of cellulose acetate is more probable than between the hydroxyl groups, which results in relative large shielding of the free OH groups in the polymer in samples with high degrees of substitution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1761–1765, August, 1989.We would like to thank N. I. Naimark for providing the samples of the cellulose acetates.     

Platinum-catalyzed allylation of aminonaphthalenes with allylic acetates

The activation of C-O bonds in allylic acetates has been accelerated by carrying out the reactions in the presence of platinum complexes associated with ligands. Platinum-catalyzed allylation of aminonaphthalenes with allylic acetates leads to N-allylic aminonaphthalenes in good yields.     

Stereospecific elimination of acetic acid in 3- and 4-arylcyclohexyl acetates under electron impact

The elimination of CH₃COOH from the molecular ions of trans-3- and 4-arylcyclohexyl acetates takes place to a greater extent than in the cis isomers. Deuterium labelling shows that the elimination involves mainly the benzylic hydrogen in the trans-acetates, but not in the cis isomers. This behaviour is similar qualitatively to that of the corresponding alcohols and methyl ethers, but entirely different from that of t-butylcyclohexyl acetates, which do not exhibit any stereospecificity. Substituent effects on the elimination for both cis and trans isomers are discussed.     

Kinetic resolution of ketone cyanohydrin acetates with a microbial enzyme

Incubation of d1-1-cyano-1-methylalkyl (or alkenyl) acetates (methyl ketone cyanohydrin acetates) with cells of IAM 4682 afforded optically active acetates and the corresponding ketones via asymmetric hydrolysis. Resulting (S)-2-cyano-2-undecyl acetate was converted to the aminofuranone derivative without losing its optical purity.