Conversion of Benzo- and Naphthonorcaradien-7-yl to Benzo- and Naphthotropyl Radicals

Article abstract of DOI:10.1021/ja00522a040

Thermal decompositions of tert-butyl 2,3-benzonorcaradiene-7-percarboxylate (7), tert-butyl 2,3-(2',3'-naphtho)norcaradiene-7-percarboxylate (8), bis(2,3-benzonorcaradiene-7-carbonyl) peroxide (9), and bis<2,3-(2',3'-naphtho)norcaradiene-7-carbonyl> peroxide (10) have been studied with particular attention paid to the hydrocarbon products, 2,3-benzonorcaradiene (11) and 1,2-benzotropilidene (12) from 7 and 9, and 2,3-(2',3'-naphtho)norcaradiene (14) and 1,2-(2',3'-naphtho)tropilidene (15) from 8 and 10.The variation of product ratio with solvent from 7 and 8 suggests that the intermediate benzo- and naphthonorcaradien-7-yl radicals competitively abstract a hydrogen atom or undergo ring opening to the corresponding tropyl radical.A similar study of 9 and 10 suggests that there is an additional, polar component to formation of seven-membered ring products 12 and 15.Since the hydrocarbon products are free radical in origin, it is suggested that the intermediates, whether highly polarized species or free cations, must revert back to free radicals before giving these products.It is further suggested that the greater degree of ring opening from the diacyl peroxides, 9 and 10, is due to the greater allowedness of the ring opening of the norcaradienyl type cations relative to the corresponding radicals.It is also demonstrated that benzonorcaradienyl intermediates undergo ring opening more readily than the corresponding naphthonorcaradienyl intermediates.