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.