Acid-catalyzed intramolecular addition of a carboxy group to vinylsilanes

In the presence of a catalytic amount of TsOH·H2O or TiCl4, 5-silyl-4-pentenoic acids (1), namely vinylsilanes with a carboxy group, were smoothly cyclized to γ-lactones in good to high yields. The difference in the geometry of the carboncarbon double-bond did not affect the reaction rate. The TiCl4-catalyzed cyclization of the substrates bearing a phenyl or alkyl group at the homoallylic position showed moderate cis-selectivity, while introduction of a substituent into the allylic position led to high trans-selectivity.