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Allyltrimethylsilane reacts with simple conjugated dienes in the presence of aluminum chloride catalyst to give stereoselective [3 + 2] cycloadducts of trans-vinylcyclopentanes in 29−72% yields at −10 °C. The same reactions give 1,4-allylsilylated compounds as the major products at −50 °C, which cyclize to the annulation products as the reaction mixture is allowed to warm to −10 °C. The reaction using (2-methyl-2-propenyl)trimethylsilane instead of allyltrimethylsilane does not give the annulation due to an unfavorable 1,2-silyl shift but, rather, allylsilylation products. The results are consistent with an initial 1,4-allylsilylation of the conjugated diene, followed by the intramolecular cyclization of the 1,4-allylsilylated alkene to the stereoselective trans-[3 + 2] cycloadduct, via a 1,2-silyl shift.

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