Photochemistry of (o-Methylphenyl)alkenes and the Stereospecific Trapping of the Resulting o-Xylylenes

Article abstract of DOI:10.1021/jo00143a023

The photochemical behavior of a series of o-methylstyrenes with simple alkyl groups in the α or β positions was investigated in order to determine the synthetic potential of the resulting o-xylylenes.The major photochemical product of all the styrenes employed (1,9,10, and 11) was the corresponding o-xylylene.The o-xylylenes were trapped in acceptable yields by maleic anhydride to give the Diels-Alder adducts.In the case of 9 or 10 and 11 the o-xylylynes were produced stereoselectively and trapped stereospecifically to give 15 or 16 respectively.In the absence ofa dienophile or in the presence of a weak dienophile, such as cyclohexene, a slower isomerization of the o-methylstyrenes to the meta isomers was observed, presumably via a benzvalene intermediate.In addition, the o-xylylene produced from 9 or 10 and 11 underwent geometrical isomerization in the absence of maleic anhydride, resulting in the formation of 10 and 11 upon irradiation of 9 and vice versa.