With
the aim of developing novel annulations via ketene intermediates,
allenyl imide and alkynoates bearing good leaving groups are used
for their function in a tandem conjugate addition–elimination
reaction (SN2′ type) promoted by nucleophilic phosphine catalysts.
By utilizing thioamides as 1S,3N-bis-nucleophiles, [3+3] and [3+2] annulations have been established
to allow rapid access to 1,3-thiazin-4-ones and 5-alkenyl thiazolones
in high yields, respectively. Furthermore, the possible reaction mechanisms
are proposed on the basis of deuterium labeling experiments and density
functional theory calculations.