Photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction: methanol, beta-myrcene, and 1,4-dicyanobenzene. Intramolecular cyclization of an ene-diene radical cation

The photochemical nucleophile-olefin combination, aromatic substitution (ph oto-NOCAS) reaction of methanol, 7-methyl-3-methylene-1,6-octadiene (beta-m yrcene, 1), and 1,4-dicyanobenzene yields five 1:1:1 adducts: cis-2-(4-cyan ophenyl)-4-(1-methoxy-1-methylethyl)-1-methylenecyclohexane (15), trans-2-( 4-cyanophenyl)-4-(1-methoxy-1-methylethyl)-1-methylenecyclohexane (16), 1-( 4-cyanophenylmethy1)-4-(1-methoxy-1-methylethyl)cyclohexene (17), 4-[4-meth oxy-3,3-dimethylcyclohex-(E)-1-ylidenyl]methylbenzonitrile (18), and 4-(1-v inyl-4-trans-methoxy-3,3-dimethylcyclohexyl)benzonitrile (19). All of these adducts are cyclic; variation in the product ratio as a function of methan ol concentration indicates cyclization is occurring, 1,6-endo, with both th e initially formed radical cation and with the intermediate beta-alkoxyalky l radicals. Evidence based upon comparison of the ionization and oxidation potential of beta-myrcene with model alkenes and with conjugated dienes ind icates the initial electron transfer involves the trisubstituted mono alken e moiety; the diene moiety, mono-substituted at a nodal position, has a hig her oxidation potential. High-level ab initio molecular orbital calculation s (MP2/6-31G*//HF/6-31G*) provide useful information regarding the nature ( relative energies and charge and spin distribution) of the intermediate rad ical cations, which supports the proposed reaction mechanism.