Investigation of Alkyne Regioselectivity in the Ni-Catalyzed Benzannulation of Cyclobutenones

A Ni-catalyzed benzannulation reaction of cyclobutenones and alkynes provides a rapid synthesis of heavily substituted phenols. The regioselectivity of this reaction can be modulated by variation of substituents on the alkyne. Though the incorporation of Lewis basic donors provides modest selectivities, the use of aryl substituents can provide high levels of regiocontrol. Finally, alkynylboronates derived from alkyl-substituted acetylenes provide both high yields and regioselectivities. This study suggests that alkynes bearing one sp2- and one sp3-based substituent can undergo benzannulation with high levels of regiocontrol whereby the sp3-based group is incorporated ortho-to the phenolic OH.