摘要：

Examination of the general sequence 2 → 7 for addition of a 13-unsubstituted phenolic C ring2 to decalones 2a-e is described. Condensation of the decalones with HCO2Et is uniformly efficient, but the rates and yields for conversion of the 8-hydroxymethylene derivatives to 8-formyl-Δ8-7-octalones by reaction with DDQ vary remarkably. Addition of the sodium enolate of MeCOCH2CO2-t-Bu to a-formyl enones 4a-d and acid-catalyzed cyclization of the adducts 5a-c to tricyclic enediones 6a-c proceed normally and in high yield. Aromatization of 6a-c by pyHBr3 affords not only 7-keto-12-phenols (7), the sole products from their 13-alkyl analogues, but also 13-bromo-7-keto-12-phenols and, at least in the case of 6a, 13-bromo-Δ13-7,12-enediones (9). Dehydrohalogenation of 9a by collidine produces 7a, a podocarpic acid model. Hydrogenolysis of the 12-(2′-benzoxazolyloxy) derivative of 7b provides tetracyclic amide 19, which has been formally converted to several diterpenoid alkaloids.15.

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