Late‐stage functionalization of Vouacapane derivatives from Caesalpinia platyloba by a Groebke−Blackburn−Bienaymé reaction

Abstract

AbstractAn almost underexplored field within the natural products area is the synthesis of pseudo‐natural product libraries by employing isocyanide‐based multicomponent reactions as powerful synthetic tools and natural products or their functionalized derivatives as starting reagents. In this work, a novel synthetic strategy behind the late‐stage functionalization of fused Vouacapane‐azoles in a two‐step reaction was developed. The first reaction is a Vilsmeier–Haack formylation at furan ring of the natural product 6β‐acetoxyvouacapane, which was isolated from the leaves of Caesalpinia platyloba from its dichloromethane extracts. The second reaction was a Groebke–Blackburn–Bienaymé reaction to synthesize the pseudo‐natural products 11a‐f in moderate yields, containing pharmacophoric fragments furan and imidazo[1,2‐a]pyridine. The compounds described here are good candidates for biological activity assays.