Rapid Route-Finding for Bifurcating Organic Reactions.

A large number of organic reactions feature post-transition-state bifurcations. Selectivities in such reactions are difficult to analyze because they cannot be determined by comparing the energies of competing transition states. Molecular dynamics approaches can provide answers but are computationally very expensive. We present an algorithm that predicts the major products in bifurcating organic reactions with negligible computational cost. The method requires two transition states, two product geometries, and no additional information. The algorithm correctly predicts the major product for about 90% of the organic reactions investigated. For the remaining 10% of the reactions, the algorithm returns a warning indication that the conclusion may be uncertain. The method also reproduces the experimental and the molecular dynamics product ratios within 15% for more than 80% of the reactions. We have successfully applied the method to a trifurcating organic reaction, a carbocation rearrangement, and solvent-dependent Pummerer-like reactions, demonstrating the power of the algorithm to simplify and to help understand highly complex reactions.