Ashok M. Salunkhe

Highly enantioselective reduction of prochiral ketones with N,N-diethylaniline·borane (DEANB) in oxazaborolidine-catalyzed reductions

Abstract A variety of prochiral ketones including phenyl, aralkyl, cycloalkyl, alkyl and tertiary alkyl are enantioselectively reduced with an oxazaborolidine catalyst (5 mol% of the Me-CBS) and N,N-diethylaniline·borane as the borane source. The enantioselectivity of the reduction produced secondary alcohols in the range of 90 to ≥99% ee.

Selective reductions. Part 60: Chemoselective reduction of organyl azides with dichloroborane–dimethyl sulfide

The rate and stoichiometry of the reduction of an organyl azide with BH3·THF was examined under standardized conditions at room temperature. Borane derivatives, such as dialkyl-, alkoxy-, and haloboranes were also examined for the reduction of azides. This study revealed BHCl2·SMe2 to be the most suitable reagent for the reduction of azides. The chemoselectivity of this reagent was also studied by reducing n-hexyl azide in the presence of representative series of functional groups, including esters, halides, nitriles, and nitro groups. BHCl2·SMe2 reduces azides in the presence of all of the above functional groups as well as olefins. Taking advantage of the differences in reactivity of BHCl2·SMe2 and BH3·THF or BH3·SMe2, it is now possible to reduce selectively an azide in the presence of olefins or to hydroborate an olefin in the presence of azides by a judicious choice of the reagent. q 2002 Elsevier Science Ltd. All rights reserved.

N,N-Diethylaniline·borane, an efficient reducing agent for reduction of representative functional groups

Abstract N,N-Diethylaniline·borane (DEANB), a thermally stable, commercially available, amine·borane reagent, reduces a variety of functional groups, such as aldehydes, ketones, carboxylic acids, tertiary amides, and lactams in excellent yields. It also reduces Schiff bases to the corresponding amines in very good yields. Besides these reducing properties, it readily hydroborates 1-octene to provide the trialkylborane which in turn on alkaline peroxide oxidation furnished the 1-octanol in excellent yield and usual regioselectivity.

Dichloroborane-Dimethyl Sulfide, A Highly Selective Reducing Agent for Reduction of Organyl Azides to Amines.

Abstract Dichloroborane-dimethyl sulfide reduces a variety of organyl azides, such as primary, secondary, tertiary, and aromatic to the corresponding amines in excellent yields. Cycloalkyl and benzylic azides are also readily reduced by this reagent. The reduction of azide with BHCl 2 SMe 2 is highly selective and many functional groups, such as halogen, ester, nitrile, aliphatic and aromatic nitro, survive in this process.

B-(2-Azido-2-propenyl)-1,3,2-dioxaborinane: A novel reagent for allylboration

Abstract A new allylborating agent, B -(2-azido-2-propenyl)-1,3,2-dioxaborinane, has been synthesized by the reaction of iodine azide with B-allyl-1,3,2-dioxaborinane, followed by dehydroiodination with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). This reagent allylborates representative aldehydes to provide, after hydrogen peroxide oxidation, the corresponding 2-azido-1-alken-4-ols in 64–75% isolated yields.

A stereoselective synthesis of (±)-trans-cycloalkanopiperidines and cycloalkanopyrrolidines via hydroboration

Abstract A highly stereoselective synthesis of trans-cycloalkanopiperidines and cycloalkanopyrrolidines has been achieved via hydroboration of bromocycloalkenes with dichloroboranes. The intermediate bromocycloalkylboronic acids were converted into azidocycloalkylboronates. Addition of two equivalents of boron trichloride in dichloromethane generated dichloroboranes which, by an intramolecular cyclisation gave intermediates 11. These can be readily hydrolyzed to get the corresponding important nitrogen heterocycles in good yields and excellent stereochemical purities.