Verbenalin is of established structure and configuration (6) and has been converted by steps not involving the asymmetry at C-2,3 and -7 into an olefin (12) also prepared from loganin; this proves that the structure and absolute configuration of loganin is as (1) apart from the centres at C-5 and C-1. The configuration at C-5 is determined by three independent methods and that of C-1 by n.m.r measurements. It is proved that the C-methyl group of loganin lies in the thermodynamically stable configuration and this knowledge allows a route by way of 5-dehydrologanin (24) for the preparation of [5-³H]loganin and [5-³H]epiloganin to be developed.

The specific incorporation of geraniol into loganin is demonstrated.