Regioselectivity in nickel(0)/phosphine catalyzed cycloadditions of alkynes and isocyanates

The regioselectivity of Ni(0)-catalyzed cycloadditions of various isocyanates and asymmetrical alkynes to afford pyridones was explored. The use of PEt3 provided, in most cases, two of the four possible pyridone regioisomers in high overall yields. Mechanistic rationale for the product distribution is provided.