Experiments on the synthesis of tetracycline. Part 16. Improved photocyclic preparation of 12-keto-derivatives and their deprotection using benzeneseleninic anhydride
Abstract
Improved methods for the photocyclisation of 4-[2-(1,3-dithiolan-2-yl)benzyl]-2-phenylnaphtho[1,8-bc]furan-5-one (6; X = Y = S) and 4-[2-(1,3-dithiolan-2-yl)-3,5-dihydroxy-4-methoxycarbonylbenzyl]-2-phenylnaphtho[1,8-bc]furan-5-one (1; X = Y = S) to their tetracyclic analogues are described. Deprotection of the C-12 thioacetal unit in the cyclised products was achieved using benzeneseleninic anhydride. Introduction of a 6α-methyl substituent and an amide grouping into C-2 of certain tetracyclic substrates provides compounds which have potential use for tetracycline synthesis.