Tin-free radical acylation and cyanation reactions

Abstract

Due to the versatility, predictability, and functional-group tolerance, free radical methodology has broaden its place in the armory of synthetic chemistry. But organotins, most frequently used reagent in radical chemistry, have many limitations for industrial application due to toxicity. To overcome this limitation of radical methodology, we investigated tin-free radical acylation and cyanation. Both of them are based on atom or group abstraction by methyl radical instead of organotin radical. This methyl radical is generated from thermal decomposition of methanesulfonyl radical which comes from methanesulfonyl oxime ether, ally) methanesulfone, and methanesulfonyl cyanide. For benzylic, tertiary and secondary iodide, our tin-free radical acylation approach worked well. But, for primary alkyl iodide, direct addition of methyl radical to sulfonyl oxime ether was faster than iodine atom transfer, thus, the yield of undesired product was higher than desired product. Utilizing phenyl telluride group, we could get satisfactory results for primary alkyl cases. Replacement of methanesulfonyl oxime ether by phenylsulfonyl oxime ether and allyl methyl sulfone gave similar result. In our tin-free radical cyanation, methanesulfonyl cyanide proved to be unsuccessful because of fast direct addition of methyl radical into sulfonyl cyanide. We found toluenesulfonyl cyanide and allyl methyl sulfone system is much better efficient for this approach.