Compounds related to biologically active steroids. 1,2,3,4,9,10-Hexahydro-6,7-dimethoxyphenanthrene-2-spirocyclohexan-2′-one

Abstract

Diels–Alder reaction of 1,2-dihydro-6,7-dimethoxy-4-vinylnaphthalene (1) and 2-methylenecyclohexanone (2), generated from a Mannich base, gave 1,2,3,9,10a-hexahydro-6,7-dimethoxyphenanthrene-2-spirocyclohexan-2′-one (3a) as two diastereoisomers: both of these could be isomerised to give the same compound, the 1,2,3,4,9,10-hexahydro-isomer (3b). Ozonolysis of compound (3a) followed by internal aldol condensation gave 5′-hydroxy-6,7-dimethoxytetralin-2-spirocyclopentane-3′-spirocyclohexane-1,2″-dione (5), the n.m.r. spectrum of which confirmed the structure (3a) and hence (3b), and ruled out the alternative phenanthrene-1-spirocyclohexane structure (4). Spiro[5,5]undecane-1,9-dione (6d) was prepared and converted into the 3,4-dimethoxyphenacyl derivative of its mono-enamine; this on acid hydrolysis gave a furan derivative (7).