Iodine(III)-promoted ring expansion of 1-vinylcycloalkanol derivatives: a metal-free approach toward seven-membered rings.

A versatile and metal-free approach for the synthesis of molecules bearing seven- and eight-membered rings is described. The strategy is based on the ring expansion of 1-vinylcycloalkanols (or the corresponding silyl or methyl ether) mediated by the hypervalent iodine reagent HTIB (PhI(OH)OTs). The reaction condition can be easily adjusted to give seven-membered rings bearing different functional groups. A route to medium-ring lactones was also developed.