Ring-C aromatic steroids. Part 4. The C-aromatic analogue of progesterone

Abstract

The ring-C aromatic analogue of progesterone, 18-norpregna-4,8,11,13-tetraene-3,20-dione (2), was formed together with its 17-epimer (3) when 9α,11α-epoxy-20ξ-hydroxy-3-oxopregn-4-eno-18,20-lactone (14) was subjected to oxidative decarboxylation, and the resulting products treated with boron trifluoride. The precursor (14) was synthesised as follows. 11α-Hydroxyprogesterone (4) was dehydrated, and the product then selectively reduced (by two routes) to 20β-hydroxypregna-4,9(11)-dien-3-one (9). The latter was functionalised at C-18 to give 3-oxopregna-4,9(11)-dieno-18,20-lactone (10) which was oxidised, after opening of the lactone ring, to the corresponding lactol (12). The latter was converted into the required lactol epoxide (14). Internal displacement on the 9α,11α-epoxide occurred when the lactol epoxide (14) was treated with acid, yielding 9α-hydroxy-3,20-dioxopregn-4-eno-18,11β-lactone (16).