Syntheses of Highly Functionalized Spirocyclohexenes by Formal 4+2 Annulation of Arylidene Azlactones with Allenoates

摘要

A straightforward phosphine‐catalyzed formal [4+2] annulation between α‐branched allenoates and arylidene azlactones has been developed to access highly functionalized spirocyclohexenes. This cyclization favors the γ‐addition of the phosphine‐activated allenoates over a β′‐addition pathway. Detailed computational studies support the proposed mechanism and provide a reasonable explanation for the observed regioselectivity and the noted effect of the catalyst.