Semi-synthesis of imidazo-5α-hydroxyvouacapane from Caesalpinia pulcherrima via a Groebke−Blackburn−Bienaymé reaction

A semi-synthetic strategy and operationally simple to obtain a new heterocyclic system imidazo-5α-hydroxyvouacapane in two-step reactions was developed. The first reaction step is a Vilsmeier-Haack formylation at the furan ring of the 5α-hydroxyvouacapane isolated from Caesalpinia pulcherrima stems to obtain the 5α-hidroxyvouacapane-aldehyde in 33% yield. The second reaction step is a Groebke−Blackburn−Bienaymé reaction to synthesize the imidazo-5α-hydroxyvouacapane by using 2-aminopyridine and tert-buthyl isocyanide in 75% yield. This work contributes significantly to semi-synthesis through multicomponent reactions, an area with limited literature coverage.