ALUMINUM-CHLORIDE CATALYZED STEREOSELECTIVE [3+2]CYCLOADDITION OF ALLYLSILANES WITH SIMPLE CONJUGATED DIENES

Alkyltrimethylsilane reacts with simple conjugated dienes in the prese nce of aluminum chloride catalyst to give stereoselective [3 + 2] cycl oadducts of trans-vinylcyclopentanes in 29-72% yields at -10 degrees C . The same reactions give 1,4-allylsilylated compounds as the major pr oducts at -50 degrees C, which cyclize to the annulation products as t he reaction mixture is allowed to warm to -10 degrees C. The reaction using (2-methyl-2-propenyl)trimethylsilane instead of allyltrimethylsi lane does not give the annulation due to an unfavorable 1,2-silyl shif t, rather, allylsilylation products. The results are consistent with a n initial 1,4-allylsilylation of the conjugated diene, followed by the intramolecular cyclization of the 1,4-allylsilylated alkene to the st ereoselective trans-[3 + 2] cycloadduct, via a 1,2-silyl shift.