The first preparation of beta-lactones by radical cyclization.

beta-Lactones have, for the first time, been prepared by 4-exo-trig radical cyclization. Thus, alpha-ethenoyloxy radicals react in the presence of tributylstannane in a photothermal process to give beta-lactones. Highest yields were obtained when groups capable of stabilizing a carbon-centered radical were present at the 3-position of the alkenoate acceptor.