Ligand-Controlled Regiodivergent Hydrosilylation of α,β-Unsaturated Esters

Silyl-substituted esters have attracted considerable interest owing to their versatile reactivity. However, current methods typically use reactive organometallics and require multiple steps, with low atom economy and narrow substrate scope. These issues limit the utility of such compounds, especially those bearing hydrogen-containing silyl groups. Herein, we present a copper-catalyzed, regioselective hydrosilylation of α,β-unsaturated esters that enables efficient and tunable access to both α- and β-silyl esters bearing Si–H functionalities. In the presence of dppm as the ligand, undesired reduction pathways are effectively suppressed, affording α-silyl esters in high yields with excellent regioselectivity. Notably, this protocol is compatible with both dihydrosilanes and trihydrosilanes, marking the first example of α-silylation of α,β-unsaturated esters using trihydrosilanes. In contrast, employing dcype as the ligand promotes an anti-Michael-type addition, delivering β-silyl esters via an unusual α-addition of Cu–H to the α,β-unsaturated system. Deuterium-labeling studies support the involvement of a distinct α-addition mechanism. Density functional theory (DFT) calculations pinpointed the stabilizing role of the weak C–H···π interaction between the dcype ligand and the aryl ring of the substrate in the regioselectivity reversed racemic β-silylation that reversed the trend to slightly favor the β-selectivity, a trend that is augmented by solvent and temperature effects.