Acid-catalyzed cyclization of vinylsilanes bearing a hemiacetal group

In the presence of a catalytic amount of TsOH .H2O, hemiacetals derived fro m (Z)-4-trialkylsilyl-3-buten-1-ols and chloral were cyclized to 2-trichlor omethyl-4-trialkylsilylmethyl-1,3-dioxanes in good to high yields. The subs trates bearing an allylic substituent achieved high levels of 1,2-asymmetri c induction. When the silyl group was a benzyldimethylsilyl group, the prod ucts could be efficiently converted to 1,2,4-triol derivatives by oxidative cleavage of the silicon-carbon bond.