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 selectivit...

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Bibliographic Details
Published in:Chemistry : a European journal 2015-02, Vol.21 (6), p.2701-2704
Main Authors: Stalling, Timo, Harker, Wesley R. R., Auvinet, Anne-Laure, Cornel, Erik J., Harrity, Joseph P. A.
Format: Article
Language:English
Subjects:
Alkynes
Aromatic compounds
Bearing
Boranes
catalysis
Chemistry
cycloadditions
Esters
Level (quantity)
Nickel
Phenols
regioselectivity
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Summary: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. The Ni‐catalyzed benzannulation of cyclobutenones and a series of alkynes highlight a preference for the incorporation of alkyl substituents at C‐2 of the phenol products. In contrast, aryl and pinacol borane esters show a preference for incorporation at C‐3. Accordingly, alkynes bearing a combination of sp2‐ and sp3‐based substituents undergo benzannulation with high levels of regiocontrol.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201405863