REMOTE-CONTROL OF STEREOGENICITY TRANSFER BY RING-GENERATED ANISOTROPIC ORBITAL OVERLAP - STEREOCHEMISTRY OF HYDROGEN SHIFT IN THE INTRAMOLECULAR REVERSE ENE REACTION OF A CIS-2-ALKYL-1-ALKENYLCYCLOPROPANE

The thermal rearrangement of cis-2-(2-propyl)-1(E)-propenylcyclopropane at temperatures near 230-degrees-C in the gas phase occurs with activation parameters of E(a) = 35.5 +/- 0.6 kcal/mol and log A = 12.05 +/- 0.5 (A, s-1). Thc optically active isotopically doubly labeled analogue (cis-2(S)-(2(S)-propyl-l-d3)-1 (S)-(1 (E)-propenyl-2-d)cyclopropane 5 was synthesized in 12 steps from dicyclopentadiene. Pyrolysis of 5 gave only 2-methyl-octa-2(Z),5(Z)-diene-l-d3-7(S)-d, with high stereospecificity at each of the three sites of stereogenicity. This result is the one predicted if the reaction is controlled by optimal overlap of the reacting C-H and pi-bond orbitals with the C(s) symmetric component of the degenerate 3E' highest occupied orbital of the cyclopropane ring.