Free radical substitutions of acyloxy groups in carbohydrate α-ketoesters

Abstract

A range of carbohydrate derivatives containing α-ketoester functionality undergo efficient reductive loss of the acyloxy groups when treated with tri-n-butyltin hydride in refluxing benzene and in the presence of azoisobutyronitrile (AIBN) as radical initiator; under similar conditions, but with allyltri-n-butyltin instead of the hydride, efficient α-C-allylation takes place with axial substitution occurring preferentially in compounds with the ketoesters located within conformationally stable pyranoid rings; the methods represent novel ways of deoxygenating carbohydrate derivatives and of introducing branch points.