Polycyclic systems. Part 19. Synthesis of 8-isobutyl-10-methyl-11H-indeno[2,1-a]phenanthrene (second diels hydrocarbon), a minor dehydrogenation product of cholesterol

Abstract

The structure of the second Diels hydrocarbon, a dehydrogenation product of cholesterol, has been confirmed as 8-isobutyl-10-methyl-11H-indeno[2,1-a]phenanthren(1) by an unambiguous synthesis. 4-Isobutyl-2-methyl-1-bromobenzene (5) prepared from m-acetotoluidide was converted by a series of standard reactions into 2,4-dimethyl-6-isobutylindan-1-one (10) which on condensation with 2-(1-naphthyl)ethylmagnesium bromide followed by cyclisation and dehydrogenation afforded the desired hydrocarbon (1), identical with the second Diels hydrocarbon in all respects.