Sequential oxidation/thermal induced intramolecular [2+2] cycloaddition of propynol-vinylidenecyclopropanes: access to novel cyclobutene-containing spiro[2.3]hexenes.

An efficient and highly regioselective synthetic method has been developed for the preparation of novel cyclobutene-containing spiro[2.3]hexenes fused with six or seven-membered carbo- or hetero-cycles in good to excellent yields following a thermal induced intramolecular [2+2] cycloaddition of alkynone-vinylidenecyclopropanes or a sequential oxidation/thermal induced intramolecular [2+2] cycloaddition process of propynol-vinylidenecyclopropanes under metal-free conditions. [ABSTRACT FROM AUTHOR]