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

Article abstract of DOI:10.1021/ja00012a032

The thermal rearrangement of cis-2-(2-propyl)-1(E)-propenylcyclopropane at temperatures near 230 °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). The optically active isotopically doubly labeled analogue (cis-2(S)-(2(S)-propyl-1-d₃)-1(S)-(1(E)-propenyl-2-rf)cyclopropane 5 was synthesized in 12 steps from dicyciopentadiene. Pyrolysis of 5 gave only 2-methyl-octa-2(Z),5(Z)-diene-1-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 π bond orbitals with the C_s symmetric component of the degenerate 3E' highest occupied orbital of the cyclopropane ring.