Chapter 10. Terpenoids and steroids

Abstract

BIOGENETIC-TYPE syntheses continue to attract attention. Cyclisation of the terminal epoxides of simpler terpenes gives polyclic systems. Of particular interest is the terminal epoxide (1) of geranylgeranyl acetate,' which, on brief treatment with stannic chloride in benzene, gives the tricyclic product (2) with six asymmetric centres all having the stereochemistry of the natural diterpenoids. Mechanisms involving either a concerted cyclisation or a stepwise process via mono-and bi-cyclic carbonium ions are proposed. The non-enzymic cyclisation of squalene 2,3-epoxide leads to the tricyclic compounds (3) and (7; R = c~H ) ( 8 ; R =