1-ALKENYLCYCLOALKOXY RADICAL CHEMISTRY - A 2-CARBON RING EXPANSION METHODOLOGY

The exploitation of alkoxy radicals derived from 1-ethenylcycloalkanols for use in a two-carbon ring expansion protocol was proposed. Direct one-pot alkoxy radical-mediated fragmentation-cyclization was not feasible since the reactive intermediate was quenched by iodine in the reaction mixture. However, via the use of iodo epoxides 3, the tandem fragmentation-cyclization sequence could be accomplished. This afforded ring-expanded products via an endo mode of cyclization, although in one example product from an exo mode of cyclization was also isolated. This methodology was shown to be valid for large ring compounds as well. The intermediary of iodo epoxides 3 also afforded improved yields as compared to the direct cyclization of iodo enones 4. These results are the first examples of radical cyclization to medium-sized carbocycles.