Buffered acetolyses of the toluene-p-sulphonates of exo- and endo-17-norkauran- and 17-norphyllocladan-16-ols

Abstract

The norkauranol tosylates (IXa) and (Xa) each furnished six acetates and three olefins on solvolysis. The equivalent norphyllocladane esters (IIIa) and (Va) gave the enantiomers of these six acetates, one additional acetate (XXIIb), and only one olefin (VI). These transformations provided a route for the conversion of (–)-kaurene (VII) into (–)-phyllocladene [enantio-(VIII)], (–)-atiserene (XXIX), and (–)-neoatiserene (XXX) and could in principle be utilised for the formation of (+)-kaurene, (+)-atiserene, and(+)-neoatiserene from (+)-phyllocladene. Mechanistic aspects of the solvolyses are discussed; in particular, a pathway, which includes a 1,2-hydride shift from C-15 to C-16, is tentatively suggested as a rationalisation of the high yield of (VI) from (Va).