Concise Synthesis of Cycloheptatrienes from Aldehydes and the Wittig Reagent Prepared from Pyruvic Ester

Abstract A novel and concise synthesis of 1,3,5-cycloheptatrienes has been developed. The reaction of 4-substituted-4-pentenal derivatives with the Wittig reagent prepared from pyruvic ester under the optimal conditions proceeded to give 1,6-di- and 1,6,7-trisubstituted-1,3,5-cycloheptatrienes in moderate yield. The synthesis is advantageous through its use of readily available reagents, milder reaction conditions compared to those previously reported, and simple manipulations. Additionally, a plausible mechanism via intramolecular [4+2]cycloaddition followed by the ring-expansion of norcarene is proposed based on the products of the reaction.