Controlling the outcome of a carbocation-initiated cyclisation

Abstract

The Z- and E-vinylsilanes, 6,6-dimethoxy-2-methyl-1-trimethylsilylhex-1-ene (6), gave only 3-methoxy-1-methylcyclohexene (7) on treatment with zinc bromide, and the allylsilane, 6,6-dimethoxy-2-methyl-3-trimethylsilylhex-1-ene (8), gave only 5-methoxy-1-methylcyclohexene (9) on treatment with tin(IV) chloride. Taken together with an earlier result, these results show that the silyl group completely controls the outcome of this carbocationic cyclisation. The syntheses of the two starting materials, (6) and (8), illustrate the usefulness of the silyl-cuprate reagent in the construction of specific vinyl- and allyl-silanes.