Functionalized cyclobutanes via Heck cyclization.

Heck-type 4-exo-trig cyclization of linear 2-enol triflate-1,5-hexadienes provides functionalized methylene cyclobutanes. Intramolecular palladium coordination can initiate beta-hydride elimination leading to 1,2-dimethylene cyclobutane derivatives, which are obtained with high selectivity if substrates having a geminal diphenyl group at Calpha are used. In parallel, formal 5-endo-trig cyclization and beta-hydride elimination form 1-methylene cyclopent-2-en derivatives.