One-Pot Synthesis of Dihydropyrans via CO Reduction and Domino Knoevenagel/oxa-Diels-Alder Reactions.

Catalytic CO reduction with phenylsilane under solvent-free conditions was linked with the one-pot synthesis of 3,4-dihydropyrans from β-dicarbonyl compounds and styrenes. The synthesis includes three processes: (1) bis(silyl)acetal formation from CO and phenylsilane and a domino reaction of (2) Knoevenagel condensation and (3) inverse-electron-demand oxa-Diels-Alder reaction. The first process was catalyzed by a pentanuclear Zn complex (0.07 mol %) to generate bis(silyl)acetals, which were hydrolyzed into formaldehyde to be used in the second step.