DEMONSTRATION OF LACK OF INVERSION OF MIGRATING ALLYL GROUP IN PHOTOCHEMICAL REARRANGEMENT OF A HEXA-1,5-DIENE DERIVATIVE

UV irradiation of trans-2-(3′-deuterioallyl)cyclohexylidenemalononitrile (XIa) induces rearrangement to allyl-1-cyclohexenylmalononitrile, in which the deuterium is still entirely at the 3-position of the allyl group but has lost its geometrical configuration (XIIa and b). Thermal Cope rearrangement of the mixture (XIIa and b) or of pure synthetic cis-isomer (XIIa) forms 2-(1′-deuterioallyl)cyclohexylidenemalononitrile (XIb). Since XIa recovered from incomplete irradiation is quite unchanged and the cis-isomer (XIIa) is stable to irradiation even in the presence of cyclohexylidenemalononitrile, the cis-trans equilibration must occur during the migration of the allyl group. © 1968.