Intramolecular Morita-Baylis-Hillman-type Alkylation of Enones

Significance

Electrophiles employed in the Morita-Baylis-Hillman (MBH) reaction have long been restricted to highly reactive, sp²-hybridized compounds such as carbonyl, imine and Michael acceptors. In this paper, the authors describe the first use of sp³-hybridized electrophiles for an intramolecular cyclization yielding five- and six-membered rings.

While ‘traditional’ MBH amine catalysts like DABCO are inefficient in promoting the cycloalkylation, trimethyl- and tributylphosphine were found to catalyze the cyclization of a variety of substrates in good to excellent yields. Bromides turned out to be the most suitable leaving group, since chlorides showed too little reactivity and iodides are prone to alkylate the catalyst, thereby yielding phosphonium salts.