Nickel-Catalyzed Dimerization/(4+2) Cycloaddition Tandem of Terminal Alkynes with Four-Membered Ring Ketones

Controlling the behaviour of terminal alkynes in metal-catalysed intermolecular tandem reactions is a formidable challenge despite the potential advantage offered by these strategies in modern synthesis. Herein, we describe that a nickel catalyst enables a tandem consisting in the rapid dimerization of terminal alkynes into 1,3-enynes and the cycloaddition of these intermediates with an azetidinone, an oxetanone and benzocyclobutenones. Significantly, the slow or sequential additions of reagents and catalysts is not required to orchestrate their reactivity. These results are in stark contrast with previous cycloadditions of terminal alkynes with those strained four-membered ring substrates, which previously led to oligomerization or cyclotrimerization, except in the case of tert-butylacetylene.