Ejabul Mondal

A useful and convenient synthetic protocol for interconversion of carbonyl compounds to the corresponding 1,3-oxathiolanes and vice versa employing organic ammonium tribromide (OATB)☆

A wide variety of carbonyl compounds 1 can be easily protected selectively as the corresponding 1,3-oxathiolanes 2 in good yields using a catalytic amount (0.01–0.1 equiv.) of n-tetrabutylammonium tribromide in dry CH2Cl2 at 0–5 °C. On the other hand, various 1,3-oxathiolanes 2 can be deprotected chemoselectively to the parent carbonyl compounds 1 employing 0.5 equivalents of organic ammonium tribromides under identical conditions in very high yields. Mild conditions, high selectivity and yield, highly efficient, less expensive, and no brominations either at the double bond or allylic position and even α- to the keto position or aromatic ring are some of the major advantages of the protocol.

An environmentally benign synthesis of aurones and flavones from 2′-acetoxychalcones using n-tetrabutylammonium tribromide

Abstract A wide variety of aurones ( 3a–f ) can be prepared exclusively from 2′-acetoxychalcones ( 1a–f ) in high yields in two steps, by bromination using n-tetrabutylammonium tribromide (TBATB) in the presence of CaCO3 in CH2Cl2–MeOH (5:2) at 0–5°C followed by cyclization of the brominated products 2a–f on treating with 0.2 M ethanolic KOH solution at 0–5°C, respectively. In contrast various flavone derivatives 6a–f can be obtained exclusively from compounds 1a–f in fairly good yields, by brominating with the same reagent in CH2Cl2, followed by dehydrobromination and finally cyclization on treating with 0.1 M NaOMe solution.

Nickel(II) chloride as an efficient and useful catalyst for chemoselective thioacetalization of aldehydes

Abstract A wide variety of acyclic and cyclic dithioacetals can be prepared chemoselectively from the corresponding aldehydes by employing a catalytic amount of nickel(II) chloride in dry CH 2 Cl 2 –MeOH (5:1) at room temperature in good yields. Some of the major advantages of this procedure are high chemoselectivity, ease of operation, high yields and also compatibility with other protecting groups.

An exceptionally simple and catalytic method for regeneration of carbonyl functionality from the corresponding 1,3-oxathiolanes

A wide variety of 1,3-oxathiolanes 1 can be chemoselectively deprotected to the corresponding carbonyl compounds 2 in good yields by employing V2O5–H2O2 catalyzed oxidation of ammonium bromide in a CH2Cl2–H2O mixture at 0–5 °C. Some of the major advantages of this procedure are its mild conditions, and that it is highly selective and efficient, high yielding, and cost-effective. Furthermore, no brominations occur at the double bond or allylic position or α to the keto position or aromatic ring.