Quantum chemical study on the mechanism of intramolecular cyclization of 2-benzyloxyphenyl trimethylsilyl ketone to give the benzofuran derivatives

Quantum chemical calculations have been performed to explore the mechanism of intramolecular cyclization of 2-benzyloxyphenyl trimethylsilyl ketone (acylsilane) to give the benzofuran derivatives stereoselectively. This reaction involves a formation of siloxycarbene intermediate and a CH bond insertion of siloxycarbene. The comparative studies on three possible insertion of siloxycarbene show that the concerted insertion of siloxycarbene into CH bond (pathway a), which needs overcoming an energy barrier of 45.1?kcal/mol, is the most unlikely pathway, and the stepwise insertion of siloxycarbene without spin multiplicity change (pathway c) is energetically more favorable than the stepwise insertion of siloxycarbene with spin multiplicity change (pathway b). More importantly, this work can provide an insight into the stereoselectivity in this reaction in atomic molecular level. The formation of siloxycarbene is calculated to be endergonic by 22.9?kcal/mol with an energy barrier of 30.2?kcal/mol, being the rate-determining step of the whole process. Copyright (c) 2011 John Wiley & Sons, Ltd.