SYNTHESIS OF THE ALL-CIS-PERHYDRONAPHTHO[1,8-BC]FURAN SYSTEM BY PHOTOCYCLIZATION

The diketone 3 was reduced to the diol which then was transformed to the tetracyclic diketal 5 by treatment with sodium in ethanol. Protection of the remaining hydroxy group was followed by hydrolysis of the dimethylketal. The resulting ketone 7 was stereoselectively converted to the tertiary alcohol by methyl magnesium chloride. Acidic retrograde aldol reaction of the tertiary alcohol led to the decalindione 10, which was partially dehydrogenated by cupric chloride under basic conditions. The resulting endione 1 cyclized by light induced hydrogen abstraction and collapse of the resulting diradical to the perhydronaphtho[1,8-bc]furan derivative.