Experiments on the synthesis of tetracycline. Part III. Michael-type cyclisation in the formation of ring B

Abstract

The cyanohydrin tetrahydropyranyl ether {VI; R = CH(CN)·O·[graphic omitted]} formed from 4-(2-formylbenzyl)-2-phenylnaphtho[1,8 bc]furan-5-one has been cyclised under basic conditions to 12β-cyano-6aα,7,12,12aα-tetrahydro-12α-tetrahydropyranyloxy-1-phenylnaphthaceno[1,12-bc]furan-6-one (XI; R¹= CN, R²= O·[graphic omitted]). This compound has been converted by stepwise reactions into 6-acetoxy-10-hydroxy-5a, 11a-dihydronaphthacene-11(6H), 12 (5H)-dione (XIII; R = Ac). Work is described in the substituted ring A condensed series that was directed towards a similar objective.