Regioselectivity of Ring Closure of 2-Thia- and 2-Sulfonyl-5-methyl-5-hexenyl Radicals

Ring closure of the α-substituted radicals 4 (X = S, SO2) is observed to be irreversible and to lead to significant amounts of the product of 6-endo cyclization. Indeed, reduction of the sulfonyl-based radical 4 (X = SO2), in which regioselectivity is believed to be controlled by a combination of both steric and FMO interactions, is found to provide an excellent route to the cyclic sulfone 7 (X = SO2) in high yield.