B(C₆F₅)₃‑Catalyzed C(sp³)–H Alkylation of Tertiary Amines with Electron-Deficient Olefins: Determinants of Site Selectivity

The reason for the site selectivity previously reported for B(C6F5)3-catalyzed C(sp3)–H alkylation of tertiary amines with electron-deficient olefins remains a mystery. The selectivity appears to be governed by the number of electron-withdrawing groups (EWGs) on the olefin: one EWG results in α-alkylation, whereas two EWGs (one on each end of the double bond) result in β-alkylation. In this study, we solved the mystery and unlocked the pathway for β-alkylation with olefins bearing only one EWG. Control experiments and density functional theory calculations provided a detailed picture of the reaction mechanism for both α- and β-alkylation. Furthermore, we demonstrated the broad scope of the β-alkylation reaction.