[3, 3]-Sigmatropic rearrangement as a powerful synthetic tool on skeletal modification of unsaturated sugars

Abstract

The development of practical, atom-economical and stereocontrolled routes to modify monosaccharides occupy a central importance in synthetic carbohydrate chemistry. This review provides an account on carbon-carbon and carbon- heteroatom bond formation as a skeleton modification on monosaccharides, through [3, 3]-sigmatropic rearrangement reactions on unsaturated sugar synthons, the generality of the reaction conditions and synthetic utilization of the resulting functionalized sugar building blocks. Major emphasis is laid on thermal rearrangement reactions, namely, Claisen, Ireland-Claisen, aza-Claisen and Johnson- Claisen rearrangements on carbohydrate-derived allyl vinyl ethers, silyl ketene acetals, allylic trichloroacetamidates and allylic orthoesters, respectively. These reactions offer a very promising prospect and permit a straightforward approach to access a large variety of biologically important, densely functionalized and novel carbohydrate mimetics. Further, examples of bioactive complex natural products, secured in high yields and profound stereoselectivity through such thermal rearrangement reactions on monosaccharides are described herein.