Reductive dimerization of (+)-(R)-pulegone. Part 10. Absolute configuration of the spiro-atom of the resulting hydroxyperhydroindene-1-spirocyclohexanones

Abstract

The reductive dimerization of (+)-(R)-pulegone [p-menth-4(8)-en-3-one] has been shown to produce two series of ketols which are derivatives of perhydroindene-1-spirocyclohexane. In this paper the absolute configuration of the spiro-carbon atom, different for the two series, has been determined by degradation of the ketols to the two geometric isomers of methyl 3-(1-methoxycarbonyl-4-methylcyclohexyl)-2,2,3-trimethylbutyrate [(13) and (14)], whose conformations are fixed by the bulkiest substituent; the 4-methyl group is axial in one of the isomers and equatorial in the other, and they show different and characteristic n.m.r. spectra.