N-Aryl Groups Are Ubiquitous in Cross-Dehydrogenative Couplings Because They Stabilize Reactive Intermediates.

The mechanism of cross-dehydrogenative coupling (CDC) reactions has been examined by experimental and computational methods. We provide a rationale for the ubiquity of the N-aryl group in these reactions. The aryl substituent stabilizes two intermediates and the high-energy transition state that connects them, which together represent the rate-determining step. This knowledge has enabled us to predict whether new CDC substrates will react either well or poorly.