Theoretical rationale for regioselection in phosphine-catalyzed allenoate additions to acrylates, imines, and aldehydes.

[reaction: see text] A rationale for regioselection in phosphine-promoted annulations of acrylates, imines, and aldehydes with allenoates has been developed using computation at the B3LYP/6-31G(d) level of theory. The computed transition states revealed that Lewis acid activation, strong hydrogen bonding (H-bonding), and minimization of unfavorable van der Waals contacts are the guiding factors responsible for regioselection. An excellent level of correlation between the calculated regioselectivities and experiment was observed.