Rangam Gopinath

Tetrabutylammonium tribromide (TBATB)-promoted tetrahydropyranylation/depyranylation of alcohols☆

Abstract Alcohols are tetrahydropyranylated rapidly in high yields in the presence of a catalytic amount of TBATB in dichloromethane at room temperature. Depyranylation to their parent alcohol is achieved in quantitative yields by merely changing the solvent to methanol.

V2O5–H2O2: a convenient reagent for the direct oxidation of acetals to esters

Abstract Both cyclic and acyclic acetals were deprotected to give the corresponding aldehydes in acetonitrile, and are transformed to methyl esters in methanol, on treatment with a catalytic quantity of V 2 O 5 and H 2 O 2 . Under identical conditions acid-sensitive alcohol protecting groups, such as tetrahydropyranyl and tert -butyldimethylsilyl ethers, were cleaved regenerating the corresponding alcohols.

Chemoselective thioacetalisation and transthioacetalisation of carbonyl compounds catalysed by tetrabutylammonium tribromide (TBATB)Dedicated to Professor Subramanian Ranganathan on the occasion of his 70th birthday.

Thioacetals and thioketals of various aldehydes and ketones were obtained directly from carbonyl compounds or by a transthioacetalisation process from cyclic O,O-acetals in the presence of dithiols and a catalytic amount of tetrabutylammonium tribromide (TBATB). Chemoselective thioacetalisation of aromatic aldehydes containing an electron-donating group in the presence of an aldehyde containing an electron-withdrawing group, aldehydes in the presence of ketones, aliphatic cyclic ketones in the presence of aromatic ketones and less hindered ketones in the presence of more hindered ketones have been achieved. A cyclic acetal containing an electron-donating group has been chemoselectively transthioacetalised in the presence of an acetal having an electron-withdrawing substituent. These selectivities are due to the intrinsic reactivity of the substrate themselves and are independent of the catalyst and reaction conditions. Shorter reaction times, mild reaction conditions, stability of acid sensitive protecting groups, high efficiencies, facile isolation of the desired products and the catalytic nature of the reagent are the attractive features of the present method.