Thermal isomerization of benzocyclobutene

Article abstract of DOI:10.1021/ja00236a038

Thermolysis of benzocyclobutene 13CH2, 99percent gives styrene labeled in the β (48percent), ortho (30percent), α (14percent), meta (4percent), and para (4percent) positions.The major labels (β and ortho) are consistent with a mechanism involving interconversions of the isomeric tolylmethylenes and the methylcycloheptatrienes.This mechanism also involves interconversion of o-tolylmethylene with o-xylylene and p-tolylmethylene with p-xylylene.A minor mechanism produces 25percent of styrene.This mechanism involves cleavage of the aryl carbon to the methylene carbon bond in benzocyclobutene followed by hydrogen transfer to produce styrene.Thermolysis of p-xylylene produced from <2.2>paracyclophane gives styrene (55percent), p-xylene (31percent), benzocyclobutene (4percent), benzene (4percent), and toluene (3percent).Thermolysis of <2.2>metacyclophane gives styrene (18percent), p-xylene (25percent), m-xylene (3percent), benzocyclobutene (1percent), benzene (7percent), and toluene (22percent).