ELECTRON-TRANSFER-INDUCED DEPROTONATION OF ALPHA-PINENE AND BETA-PINENE - EVIDENCE FOR RING-CLOSED VINYLCYCLOBUTANE RADICAL CATIONS

Electron transfer from alpha- (1) or beta-pinene (2), to 2,3,5,6-tetra chlorobenzoquinone generates radical cations, which are rapidly deprot onated by the semiquinone radical anion. (1S,5S)-2 is converted to (1S ,5S)-1 and (1R,5R)-1 yields a dehydrogenation product, verbenene, (1R, 5R)-9 with essentially quantitative retention of optical: activity. Th e results support chiral, ''ring-closed'' radical cation structures in which the allylic-quaternary cyclobutane C-C bond retains a significa nt degree of bonding. Copyright (C) 1996 Elsevier Science Ltd