Bismuth(III) nitrate pentahydrate - A versatile reagent in organic synthesis

Abstract

(A) Montmorillonite impregnated with Bi(NO3)3· 5H2O was found to be an excellent reagent for aromatic nitration in high yield. The same group has also explored the nitration of few phenolic compounds and β-lactams. (B) Montmorillonite impregnated with Bi(NO 3)3·5H2O was also found to be an excellent reagent for the oxidation of a variety of alcohols in excellent yield. (C) Ketoximes undergo facile deprotection in acetone-H2O (9:1) in the presence of 0.5 equivalent of Bi(NO3)3·5H 2O. This method is an attractive alternative to existing routes for the deprotection of oximes. Banik and co-workers have also demonstrated the utility of this reagent for the facile deprotection of various hydrazones and oximes. (D) Bi(NO3)3·5H2O has been found to be an outstanding catalyst for the protection of carbonyl compounds such as acetals, ketals, mixed ketals and thioketals with an excellent yield. (E) Silica-supported Bi(NO3)3·5H2O [BNP-silica] was prepared under simple co-grinding conditions. The iodination of aromatic compounds using [BNP-silica] and molecular iodine under solvent-free conditions has been described. The reaction occurs in the solid state at room temperature, yielding the corresponding monoiodo derivatives in good yields. However, less activated aromatics required longer reaction time with comparatively lesser yield. (F) A variety of thioamides and thioureas are rapidly transformed to their oxo derivatives with Bi(NO3) 3·5H2O in excellent yields. However, thiono esters and thioketones are converted to the corresponding carbonyl compounds in only poor yields. The selective deprotection of thioamides and thioureas in the presence of thiono esters and thioketones make this method an attractive alternative to the existing routes for deprotection of thiocarbonyl compounds. (G) A Bi(NO3)3·5H2O-catalyzed versatile Michael reaction, developed to reduce the complications that characterize the current standard Michael reaction, has been used for facile preparation of organic compounds of widely different structures. For example, several substituted amines, imidazoles, thio compounds, indoles and carbamates were prepared at room temperature by this method. In contrast to the existing methods using acidic catalysts, this method is very general, simple, high yielding, environmentally friendly, and oxygen- and moisture-tolerant. However, the promoting role of Bi(NO3)3·5H2O in this reaction is not understood at this time. © Georg Thieme Verlag Stuttgart.