Probing the role of solvation in predicting the π-facial selectivity of 5-Fluoro-2-methyleneadamantane with per-acid: A case study

Abstract

Many qualitative, semi-quantitative and transition state models have been developed to rationalize and predict the π-face selectivity of various nucleophilic, electrophilic and radical organic reactions. However, there are cases where such models and theories are unable to explain the face selectivity. 5-Fluoro-2-methyleneadamantane (I) represents one such case to understand the stereoinduction with per-acid, where much discussed orbital and electrostatic models fail to explain the observed stereoselectivity. This work is focused with the rationalization and prediction of stereoselective electrophilic addition of per-acid to I using quantum chemical and molecular dynamics studies. The importance of solvent in controlling the π-face selectivity of I is reported employing ab initio and DFT studies. We have also presented here the effect of distortional asymmetry in the π-face of 5-Fluoro-2-methyleneadamantane (I) in solvent, which leads to predict the correct observed stereoselectivity. The ab initio molecular dynamics (AIMD) calculations attribute the asymmetric distortions in the ground state of I, which can be a constituent of the bulk transitional state differential for this reaction. The sterically unbiased olefins 4-substituted 9-methylenenorsnoutanes (II) and 5,6-cis,exo-disubstituted bicyclic[2.2.2]oct-2-enes (III) have also been studied as reference in the present study.