Polycyclic systems. Part 17. Proton nuclear magnetic resonance spectra of some 11H-lndeno[2,1-a]phenanthrene derivatives; structure of the C26 hydrocarbon (second diels hydrocarbon) from cholesterol
The n.m.r. spectra of a number of 11H-indeno[2,1-a]phenanthrenes, including the C26 hydrocarbon (second Diels hydrocarbon) from cholesterol, and their 11-oxo-derivatives have been studied. These data together with some previous observations identify the hydrocarbon as 8-isobutyl-10-methyl-11H-indeno[2,1-a]phenanthrene (21), its formation being rationalised in terms of 1,2-shift of the side chain in ring D, followed by a similar shift of the 13-methyl group and its final inclusion in ring E of the indenophenanthrene (21).