DBU catalyzed (3 + 3) annulation of β′ and δ-acetoxy allenoates with benzo-oxathiin-dioxide and phenylthiazolone: Synthesis of pyrano-oxathiines and pyrano-thiazoles

Annulation reactions involving acetoxy allenoates and enolizable carbonyl substrates under DBU (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene) catalysis is described in this paper. Thus DBU catalyzed (3 + 3) annulation reactions of acetoxy allenoates with the bifunctional nucleophiles benzo-oxathiin-dioxide and phenylthiazolone afford fused 4H-pyrans. Both β′-acetoxy allenoates and δ-acetoxy allenoates undergo this annulation to give pyrano-oxathiines or pyrano-thiazoles.

Acetoxy allenoates undergo facile (3 + 3) annulation with benzo-oxathiin-dioxide and phenylthiazolone under DBU catalysis to afford pyrano-oxathiines and pyrano-thiazoles.