An efficient synthesis of 3,4-dimethylidene oxacycles including oxolanes and oxepanes through Prins-type cyclization of hydroxy(allenylmethyl)silanes is described. We have shown that 2-substituted tetrahydrofuran derivatives could be produced by using this strategy although the 5-endo-trig cyclization mode is stereoelectronically disfavored. We also applied our method to the stereoselective synthesis of 2,7-cis-3,4-dimethylidene oxepanes, which were used for constructing more complex ring systems, such as polyether bicycles or tricycles.

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