Experiments on the synthesis of tetracycline. Part IV. Ring B formation through 1,3-dipolar additions

Abstract

The model compound 4-(2-formylbenzyl)-2-phenylnaphtho[1,8-bc]furan-5-one (I; R = CHO) has been converted into the corresponding N-phenyl-6aβ, 12β-epoxyiminonaphthaceno[1,12-bc]furan-6-one (II; R = H) by treatment with N-phenylhydroxylamine. Conversion of this intermediate into 6β-acetoxy-12β-anilino-6aα,7,12,12aα-tetrahydro-1-phenyl-6H-naphthaceno[1,12-bc]furan (X; R¹= OAc, R²= H, R³= H) is described. A method for converting certain N-arylalkylamines into the corresponding imines has been developed, and the application of this oxidation to the synthetic sequence is elaborated. Finally, the successful application of the cyclisation procedure to produce tetracyclic substances bearing substituents in ring A is described.