STEREOCHEMISTRY OF THE THERMAL ISOMERIZATIONS OF (1R,2S)-1-(E-1-PROPENYL)-2-PHENYLCYCLOPROPANE TO 3-METHYL-4-PHENYLCYCLOPENTENES

When (1R,2S)-trans-1-(E-1-propenyl)-2-phenylcyclopropane is heated at 234.4 degrees C in the gas phase, it is isomerized reversibly to its (1S,2R) enantiomer and to the enantiomers of cis-1-(E-1-propenyl)-2-phenylcyclopropane as the four isomers of 3-methyl-4-phenylcyclopentene are formed more slowly. Kinetic and stereochemical evidence indicates that this vinylcyclopropane to cyclopentene rearrangement takes place with the participation of all four possible stereochemically distinct reaction paths: the relative contributions are 44% si, 20% ar, 25% sr, and 11% ai. This stereochemical pattern is substantially similar to those determined previously for the rearrangements of three chiral trans-1-alkenyl-2-methylcyclopropanes, a result reinforcing the perception that the stereochemistry of the rearrangement is controlled neither by orbital symmetry factors nor by the relative moments of inertia or radical-stabilizing capacities of substituent groups.