Lewis acid-catalyzed three-component condensation reactions of aldehydes, alkoxysilanes, and allenylsilanes: synthesis of α-propargyl ethers

Lewis acid-catalyzed reaction of acetals with allenylsilanes and the three-component reactions of aldehydes, alkoxysilanes, and allenylsilanes are described. Both reactions are strongly dependent on the substituent at the α-position of allenylsilanes. Allenylsilanes having bulky substituents such as the tert-butyl and isopropyl groups result in the corresponding α-propargyl ethers in high yields, whereas allenylsilanes having the methyl and ethyl groups afford not only the corresponding α-propargyl ethers in low yield but also cyclopropyl ketones and α,β-unsaturated ketones as by-products.