Tin-free radical acyl cyanation using alkyl allyl sulfones as precursors

Abstract

Acyl cyanides are useful intermediates for the synthesis of cr-keto compounds and heterocycles. Recently, Ryu reported the generation of acyl radicals by trapping carbon monoxide by alkyl radicals generated by organotin reagents. In spite of this effectiveness of organotin reagents in radical mediated reactions, however, the toxicity and the difficulty of removing tin residues were serious obstacles for large-scale industrial application. To solve these problems, we investigated tin-free radical approach with alkyl allyl sulfones as radical precursors. In order to broaden the synthetic utility of our approach, we studied radical acyl cyanation using alkyl allyl sulfones as radical precursors. Radical reaction of alkyl ally) sulfones with p-toluenesulfonyl cyanide in heptane under 95 atm carbon monoxide pressure afforded the corresponding acyl cyanides. Since acyl radical formation occurs prior to the direct cyanation of alkyl radical at reasonably low carbon monoxide pressure, this method worked well with most alkyl radicals including sterically bulky tertiary alkyl radicals.