Invited
Metal-free catalytic reductive cleavage of enol ethers

In contrast to the well-known reductive cleavage of the Alkyl−O bond, the activation of Alkenyl−O is more challenging and way more rare, especially by metal-free approaches. Unexpectedly, a Alkenyl−O bond was cleaved when enol ethers were reacted with Et₃SiH in the presence of a catalytic amount of B(C₆F₅)₃, leading to alkoxysilanes and alkenes. Supposedly, this reaction is a result of a B(C₆F₅)₃ catalyzed tandem hydrosilylation reaction of the C=C double bond of the alkenyl group, followed by Lewis acid catalyzed, silicon-assisted β-elimination. This hydrosilylation-elimination reaction sequence gives, formally, a nucleophilic vinylic substitution (S_NV) of alkoxy group by the hydride of the Et₃SiH. This reactivity was probed with different alkyl and silyl enol ethers and the mechanism of this cleavage reaction was studied both experimentally and by density functional theory (DFT) calculations.