Reaction of highly methylated 2-methylenecycloalkyl hydroperoxides with FeSO4/CuCl2.: Remarkably efficient 5-endo-trig or 6-endo-trig cyclization of the intermediate carbon radicals

Treatment of 1,3,3 4,4,5,5-heptamethyl-2-methylenecyclopentyl hydroperoxide, derived from a singlet oxygen ene reaction of 1,2,3,3,4,4,5,5-octamethylcyclopentene, with FeSO4/CuCl2 gave 1-chloro-2,2,3,3,4,4-hexamethylcyclopentyl methyl ketone in high yield, suggesting that the consecutive O-O and C-C bond fission is followed by a novel 5-endo-trig cyclization of the intermediate carbon radical to the activated C-C double bond. In the case of 1,3,3,6,6-pentamethyl-2-methylene-1-cyclohexyl hydroperoxide also, an efficient 6-endo-trig cyclization of the corresponding carbon radical was realized giving 1-chloro-2,2,5,5-tetramethylcyclohexyl methyl ketone in high yield.