(The) effect of alkoxy group in radical-mediated fragmentation reactions

Abstract

The effect of alkoxy group in radical-mediated fragmentation reactions has been investigated. The radical-mediated fragmentation reactions of enol ethers attached to alkyl iodide with Bu$_3$SnH/AIBN afforded the mixture of nonfragmented products (reduced product and cyclized product) and fragmented products (ring-expanded product and recyclized product). Among several enol ethers attached to alkyl iodide, 7-membered silyl enol ethers gave the best results and they can be utilized as a useful method for the synthesis of different ring-sized-bicyclic compounds from initial bicycles. The comparative radical reaction of compound 19 and 28 showed that the ring-expansion via $\beta$-fragmentation can be facilitated by the presence of alkoxy group. The oxygen-centered radical-mediated fragmentation reactions of enol ethers attached to alkyl nitrate ester under radical conditions have been investigated. These enol ethers had been cleaved through the radical pathway to the ring-expanded products in relatively low yields.