Ligand -controlled nickel-catalyzed C–O bond cleavage of silyl enol ether for the divergent synthesis of aryl alkenes and silicon-containing product

Abstract

Silyl enol ethers are easily prepared from available ketones that are widely used as α-carbon nucleophiles in organic synthesis. However, it is challenging to use this motif as electrophiles via the activation of the alkenyl C(sp²)–O bond. Here, we report a ligand-controlled nickel-catalyzed C(sp²)–O bond activation of the silyl enol ether for the divergent formation of styrenes, benzyl silane and alkenyl silanes, respectively. In the presence of the PCy₃ ligand, the (PCy₃)Ni–H formed in situ preferably inserts into the more electron-rich C–C double bond of the silyl enol ether so that the product stays in the olefin stage (23 examples). When electron-rich ICy·HCl is used as the ligand, the Ni–H species could be inserted into silyl enol ether and the styrene derivatives formed in situ are further converted into benzyl silane products (29 examples). In addition, the Ni(0)/PCy₃/hydride acceptor (1-octene) system can form the active Ni–[Si] intermediate in situ, which can react with the styrenes intermediate to construct alkenyl silanes (3 examples). The utility of the methodology is demonstrated by gram-scale reaction and late-stage modification of complex molecules, whereby a diverse set of functional groups can be tolerated. DFT calculations explain the divergent synthesis: the (PCy₃)Ni(I)–H species prefers to insert the electron-rich C–C double bond of silyl enol ether and the (NHC)Ni(I)–H species can insert not only the electron-rich C–C double bond but also continue to insert electron-poor styrenes.