Understanding the sigmatropic shifts of cyclopenta-2,4-dien-1-yltrimethylsilane in its Diels-Alder addition.

To understand its dynamic processes in the Diels-Alder addition, temperature-dependent dynamic processes of cyclopenta-2,4-dien-1-yltrimethylsilane [1-(C5H5)Si(Me)3] are investigated by DFT computations. The degenerate sigmatropic migration of Si(Me)3 is found to be the dominant factor with a Gibbs free energy of activation of 13.2 kcal mol-1. The contribution from suprafacial hydrogen shifts is negligible, and the antarafacial sigmatropic hydrogen shifts are excluded due to their relatively high Gibbs barriers. Thermodynamically controlled Diels-Alder addition is obtained, which involves the critical interconversion between the 2,4-dienyl isomer 1 and 1,4-dienyl isomer 3.