Tetra-n-butylammonium tribromide

Abstract

(A) Preparation of a wide variety of flavones and aurones starting from 2′-acetoxychalcones 1 in high yields (36-55% and 65-85%, respectively) was accomplished in two steps, being the first selective bromination with TBATB (70-80% for 2 and 75-85% for 3). (B) Direct condensation of various alcohols and carboxylic acids was efficiently achieved with a catalytic amount of TBATB under solvent-free conditions at reflux. Chemoselectivity for primary alcohols was observed when secondary and phenolic alcohols were also present. (C) Selective protection of various carbonyl compounds to the corresponding 1,3-oxathiolanes was performed with catalytic amount of TBATB. Chemoselective deprotection of synthesized 1,3-oxathiolanes to the parent carbonyl compounds was also obtained with TBATB. No bromination on α-keto position, aromatic ring, allylic position or double bond was observed. (D) Gosain and Sharma described the kinetics and mechanism for oxidation of vicinal and non-vicinal diols to the corresponding aldehydes and hydroxycarbonyl compounds, respectively. Excellent yields were obtained. (E) Solvent-free, chemoselective diacylation of aldehydes was accomplished using a catalytic amount of TBATB, without side reaction yielding brominated products. Chemoselective cleavage of diacylates was also reported with TBATB when the reaction was performed in different conditions. (F) TBATB promotes tetrahydropyranylation and detetrahydropyranylation of primary, secondary and tertiary alcohols when present in 10 mol%. Mild reaction conditions make both reactions compatible with other acid-sensitive groups such as OTs, nitro and Boc, among others. © Georg Thieme Verlag Stuttgart.