cis,trans-Cyclohepta-1,3-diene as a transient intermediate in the photocyclization of cis,cis-cyclohepta-1,3-diene

Abstract

The photocyclization of cis,cis-Cyclohepta-1,3-diene (1) to give bicyclo[3.2.0]hept-6-ene (2) proceed through a two-step process, in which the cis,cis-isomer (1) isomerizes photochemically to the highly strained cis,trans-cycloheptadiene (5) which in turn cyclizes thermally to give the bicycloheptene (2); the cis,trans-isomer (5) was trapped chemically by acidic methanol at room temperature to give the methanol adducts (3) and (4), and was detected spectroscopically upon low-temperature irradiation.