Half rotations leading to retention of stereochemistry in epoxide ring opening by selenocyanate ion: Insights from DFT modeling

摘要

Stilbene oxide on reaction with selenocyanate ion in methanol (Culvenor et al., J Chem Soc 1949, 278) has been found to yield the corresponding stilbene with the deposition of metallic Se. For this reaction, a tentative mechanism involving "two half rotations" around the carbon-carbon bond based on the observed stereospecificity and formation of episelenide intermediate has been suggested. This reaction has been modeled at B3LYP/6-31+G(d) level and the potential energy surface of the reaction has been explored. Computations suggest a backside attack of the selenocyanate ion to one of the epoxide carbon atoms to form a prereactive complex, two successive half-rotations around the carbon-carbon bond in the opposite direction, the formation and decomposition of episelenide intermediate, and finally trans-stilbene. Calculations besides agreeing excellently with experiment reveal many interesting mechanistic details that experimentalists could not unravel. Wiberg bond order analyses reveal the smooth progress in the bond changes during the course of the reaction. Solvent effect through PCM model calculations with methanol as solvent does not alter the gas phase results significantly.