The total synthesis of (+)-petasin and (+)-isopetasin

Article abstract of DOI:10.1055/s-1997-1492

Petasin 1 and isopetasin 2, anti-inflammatory and analgesic components of the butterbur (Petasites hybridus), were prepared for the first time in a short and enantioselective synthesis. The key steps were a Michael addition/alkylation (7 → 8), an enamine alkylation to give 9 and a cyclization with N-phenyliminoketenylidenetriphenylphosphorane 11 (10 → 15).