[2,3]-sigmatropic rearrangements of hydrogen and alkyl 3-propenyl sulfoxides: A computational study

摘要

The [2,3]-sigmatropic rearrangements of hydrogen and alkyl 3-propenyl sulfoxides (R = H, CH3, CF3, CCl3) to the corresponding 3-propenyl sulfenates have been examined computationally using HF, MP2, and B3LYP with the 6-31G(d), 6-31+G(d,p), 6-311+G(d,p), 6-311+G(2d,2p), 6-311+G(3d,2p), and cc-pVTZ basis sets. The relative energies (E-rel) of the respective isomeric sulfoxides and sulfenates are sensitive to the level of theory and to electron correlation. The sulfenate is more stable in the gas phase, and the more polar sulfoxide is more stable in aqueous medium. The rearrangements are concerted, and the endo and exo five-membered transition states are very close in energy (Delta E = <1 kcal/mol). MP2/6-311+G(3d,2p) predicted the activation barriers for the sulfoxide-sulfenate rearrangements to be [kcal/mol, (R)] 19.0 (H), 21.4 (CH3), 19.3 (CF3), and 21.8 (CCl3), respectively. (C) 2006 Wiley Periodicals, Inc.