Modification of the vinylogous aldol condensation - Another approach to the synthesis of C(15)-alkylidene and benzylidene andrographolide derivatives

Abstract

A two-step protocol for the synthesis of 15-alkylidene and benzylidene derivatives of 14-deoxy-l 1,12-didchydroandrographolide. which was conducted through a dehydration reaction of androerapholide and a vinylogous aldol condensation between α, β-unsaturated butenolide moiety and benzaldehyde derivatives lias been developed. Combining with various experiments on new catalysts for these reactions: the dehydration of andrographolidc by concentrated H₂SO₄ and the vinylogous aldol reaction by K₂CO₃ in McOH or a mixture of CH₃COOH/pyrrolidine in McOH, this research has determined the optimized conditions for those catalysts and the new approach to this aldol-like reaction. All compounds synthesized were characterized by the analysis of IR, NMR, HRMS spectra.