An in Situ Approach to Nickel-Catalyzed Cycloaddition of Alkynes and 3-Azetidinones.

An efficient and convenient procedure that generates the active Ni(0) catalyst in situ from cheap, air stable Ni(II) precursors is developed for the [4 + 2]-cycloaddition of alkynes and 3-azetidinones. The reaction affords useful 3-dehydropiperidinones in comparable yields to the reported Ni(0) procedure. Additionally, the cycloaddition with 3-oxetanone afforded the 3-dehydropyranone product. Chiral 2-substituted azetidinones were also tolerated to form substituted dehydropiperidinones in high yield and enantiomeric excess.