Synthetic studies in the diterpene series. Part VII. Cyclisations of 4,8-dimethyl-1-phenylnon-7-en-4-ol and 2,6-dimethyl-9-phenylnona-2,6-diene and their mechanism

Abstract

Cyclisation of 4,8-dimethyl-1-phenylnon-7-en-4-ol (I) has been reinvestigated on a quantitative basis. Contrary to a previous report, the major product is not the trans-podocarpa-8,11,13-triene (V) but the hydrophenalene derivative (VII). Oxidation of the mixture with chromic acid, however, enriches the former component as a ketone. Cyclisation of the corresponding diene (IV) gives a preponderance of trans-podocarpatriene (>50%). A nonconcerted mechamism has been suggested for this cyclisation.