Aluminum chloride catalyzed stereoselective [3+2] cycloaddition of allylsilanes with simple conjugated dienes

Alkyltrimethylsilane 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 degrees C. The same reactions give 1,4-allylsilylated compounds as the major products at -50 degrees C, which cyclize to the annulation products as the reaction mixture is allowed to warm to -10 degrees 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, 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.