1,3-Dienones and 2H-Pyran-2-ones from Soft α-Vinyl En-olization of β-Chlorovinyl Ketones: Defined Roles of Bronsted and Lewis Base

The eliminative reaction pathways of (E)-beta-chlorovinyl ketones were investigated in the presence of both Bronsted and Lewis bases. The Bronsted base, Et3N, effected the soft alpha-vinyl enolization of (E)-beta-chlorovinyl ketones to [3]cumulenol intermediates; in turn, a catalytic amount of Lewis base, PPh3, initiated isomerization to provide 1,3-dienones in high yields. The introduction of a carbon-based nucleophile into the reaction mixture provided the highly efficient synthetic route to 2H-pyran-2-ones in one pot, where the carbon-based nucleophile generated by an extra equivalent of Bronsted base, Et3N, attacked the electrophilic [3]cumulenol intermediates to initiate cyclization to give 2H-pyran-2-ones.