Progress towards an intramolecular Diels–Alder ring-expansion approach to taxinine: the interplay of Lewis acids and high pressure

A concise route to a bicyclo[4.2.1] ring system, based on an intramolecular Diels–Alder reaction, has been developed. Preliminary results on the interplay between Lewis acids and high pressure to facilitate the reaction are described. Products with isomerized double bonds were obtained with 1 equivalent of Lewis acid at 0°C. The stereochemistry of these compounds has been determined by X-ray crystallography. Double bond isomerization is suppressed by the use of excess Lewis acid at −78°C or high pressure.