Electron transfer induced deprotonation of α- and β-pinene: Evidence for ring-closed vinylcyclobutane radical cations

Abstract

Electron transfer from α- ( 1) or β-pinene ( 2), to 2,3,5,6-tetrachlorobenzoquinone generates radical cations, which are rapidly deprotonated 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. The results support chiral, “ring-closed” radical cation structures in which the allylic-quaternary cyclobutane CC bond retains a significant degree of bonding.