Functionalized Cyclobutanes via Heck Cyclization.

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