J. V. Bhaskar Kanth

Convenient methods for the reduction of amides, nitriles, carboxylic esters, acids and hydroboration of alkenes using NaBH4/I2system

Abstract Reaction of amides with NaBH4-I2 system in THF gives the corresponding amines in 70–76% yields. Reduction of nitriles yields the corresponding amines in 70–75% yields. The I2/NaBH4 system is useful in the hydrocarboration of olefins and the corresponding alcohols are obtained in 78–92% yields after H2O2/OH− oxidation. The reagent system is also useful for the reduction of carboxylic esters and acids to the corresponding alcohols in 60–90% yields.

Convenient method for the synthesis of chiral α,α-diphenyl-2-pyrrolidinemethanol

Abstract A simplified, convenient synthesis of chiral α,α-diphenyl-2-pyrrolidine-methanol involving one step N-and O-protection of S-proline using ethylchloroformate followed by Grignard addition-alkaline hydrolysis (KOH/CH 3 OH) is described.

A SIMPLE CONVENIENT METHOD FOR THE RESOLUTION OF RACEMIC 2,2'-DIHYDROXY-1,1'-BINAPHTHYL USING (S)-PROLINE

Abstract The racemic mixture of 2,2′-dihydroxy-1,1′-binaphthyl has been resolved to obtain the R(+) and S(−) enantiomers in essentially pure forms by refluxing with (S)-proline (1eq.) in benzene in three successive operations.

Convenient procedures for the asymmetric reductions utilizing α,α-diphenyl- pyrrolidinemethanol and borane complexes generated using the I2/NaBH4 system

Abstract Syntheses of oxazaborolidine in situ in benzene using α,α-diphenylpyrrolidinemethanol and diborane, generated from the iodine-sodium borohydride system are described. The oxazaboro- lidine (10 mole%), generated by the reaction of α,α-diphenylpyrrolidinemethanol and diborane in benzene followed by heating with N,N-diethylaniline, in combination with boranetetrahydrofuran complex reduces acetophenone to 1-phenylethanol in 94.7% ee.

Asymmetric reduction of prochiral aromatic ketones by Borane–Amine complexes in the presence of a chiral amine–BF3 catalyst

The (–)-N-α-Methylbenzyl-3,5-dihydrodinaphthazepine–BH3 complex reduces aromatic ketones to alcohols with 11–57% enantiomeric excess (e.e.) in the presence of BF3·OEt2, the (–)-N-α-methylbenzyl-3,5 dihydrodinaphthazepine–BF3 complex catalyses asymmetric reduction of acetophenone by N,N′-diethylaniline–BH3 to give α-phenylethyl alcohol in 51% e.e.

Asymmetric reduction of prochiral aromatic ketones by borane–amine complexes in the presence of chiral amine–BF3 catalysts

The borane complexes of (S)-(–)-N,N-dibenzyl-1-phenylethylamine 1. (S,S)-(–)-N,N-bis(1-phenylethyl)-1-phenylethylamine 2, (–)-2-phenyl-1-(1-phenylethyl)pyrrolidine 3, (–)-7-(1-phenylthyl)-4,5-dihydro-3H-dinaphth[2,3-c;2′,3′-e]azepine 4 and 1-(1-phenylethyl-3,4-diphenyl-pyrrolidine 5 have been prepared and used to reduce prochiral aromatic ketones to alcohols in 10–57% e.e. in the presence of BF3·OEt2. The complex 4·BF3 catalyses asymmetric reduction of acetophenone by N,N′-diethylaniIine–BH3 to give 1-phenylethyl alcohol in 51% e.e. A transition state consisting of a chiral amine·BF3·BH3 complex and the ketone is proposed to explain the transformation.

Convenient Method for N-Debenzylation of Tertiary Amines

Abstract N-Benzyl tertiary amines on reaction with ethyl chloroformate give the corresponding debenzylated N-carbamates which on treatment with I3B:N(C2H5)2Ph complex yield the secondary amines.

Convenient Method for the Synthesis of N-(Ethyloxycarbonyl) Ester Derivatives from Amino Acids

Abstract Amino acids upon treatment with ethyl chloroformate in methanol in the presence of potassium carbonate give the corresponding N-(ethyloxycarbonyl) amino acid ester derivatives in good yields. These derivatives can be also synthesized by performing the reaction in THF in the presence of alcohols.