Toward Selective Reactions with CH Bonds: A Rationale for the Regio- and Stereochemistry of Dichlorocarbene Insertions into Cyclic Hydrocarbons

Abstract

DFT calculations have been performed to study the course of dichlorocarbene insertion reactions into alkanes and to better understand the regio- and stereoselectivities observed. At the B3LYP/6-31G(d) level of theory, the selectivity of dichlorocarbene insertions into a number of hydrocarbons agrees well with the obtained experimental results. The reactivity of a specific C-H bond is determined by the capacity of the remaining alkyl fragment to effectively delocalize the partial positive charge buildup during the reaction. This activity can readily be estimated by calculation of the hydride transfer potential (HTP). A comparison with the structure and the stability of the corresponding cation is useful to emphasize the origins of the selectivity. Dichlorocarbene is also predicted to react efficiently with acidic C-H bonds through a nucleophilic-electrophilic mechanism. In principle, an attack of a carbene on an appropriately substituted three-membered ring may lead to fragmentation of the molecule.