The garryfoline–cuauchichicine rearrangement: a study of the mechanism in the (–)-kaurenols

Abstract

The mechanism of the garryfoline–cuauchichicine rearrangement has been investigated using the epimeric (–)-kaur-16-en-15-ols as models. The 15β-ol is shown to rearrange rapidly in mineral acid at room temperature to 16R-(–)-kaur-15-one by a 15,16-hydride shift. The 16α-ol, like veatchine, is stable under these conditions. The contrast in the ability of these epimeric alcohols to undergo 15,16-hydride shifts is discussed.

Under the same conditions, (–)-kaur-15-en-17-ol gives the allylic isomer, (–)-kaur-16-en-15α-ol, but, under more forcing conditions, it yields 16S-(–)-kauran-17-al.