REARRANGEMENTS OF TRICYCLIC KETONES - [3.3.3]PROPELLANE FORMATION VIAA GAMMA-ENOLATE REVEALED IN AN APPROACH TO THE PENTALENENE SKELETON THROUGH BETA-ENOLIZATION

The known isomerization of the tricyclo[5.3.1.0(1,5)]- to the [6.3.0.0 (1,5)]undecane skeleton by beta-homoenolization led to examination of yl-6-methoxymethyltricyclo[5.3.1.0(1,5)]undecanone (6) as a potential precursor for the synthesis of pentalenene, a naturally occurring sesq uiterpenoid, utilizing a beta-enolate rearrangement as a key step. Whi le the anticipated rearrangement of 6 occurs, it is a minor process. T he major rearrangement product arises by generation of a gamma-enolate intermediate from a tricyclic enone formed by loss of methanol from 6 . This constitutes a new route to [3.3.3]propellanes and provides a th ird example of gamma-enolate rearrangement. Structures of the products were established primarily from their H-1 and (13)Cmr spectra.