Precise control over the selectivity of a reaction is a fundamental target. While great advances have been obtained in achieving stereocontrol, the selective manipulation of functional groups within a substrate (chemoselectivity) is still a challenge. The cyanation of aldehydes offers an illustrative example: the 1,2-addition of nucleophilic cyanide to the aldehydic group was one of the first examples of a stereoselective catalytic process. By contrast, the conjugate cyanation of linear α,β-unsaturated aldehydes has remained elusive, even in a racemic variant. The main difficulty lies in achieving 1,4-chemoselectivity over the preferred cyanide 1,2-addition. Here, we report an asymmetric catalytic method to achieve the exclusive conjugate cyanation of enals. The synergistic action of a chiral organocatalyst with a visible-light-activated photoredox catalyst promotes the single-electron reduction of enals, inducing a formal inversion of polarity. The resulting chiral radical, being nucleophilic in character, is then intercepted by an electrophilic cyanide source with perfect 1,4-chemoselectivity and good stereocontrol.

精确控制反应的选择性是一个基本目标。虽然在实现立体控制方面取得了很大进展，但底物内官能团的选择性操作（化学选择性）仍然是一个挑战。醛的氰化提供了一个说明性的例子：亲核氰化物 1,2-加成到醛基是立体选择性催化过程的第一个例子。相比之下，线性 α,β-不饱和醛的共轭氰化仍然难以捉摸，即使是外消旋变体。主要困难在于实现 1,4-化学选择性优于首选氰化物 1,2-加成。在这里，我们报告了一种不对称催化方法来实现烯醛的专有共轭氰化。手性有机催化剂与可见光激活的光氧化还原催化剂的协同作用促进了烯醛的单电子还原，从而导致极性的形式反转。由此产生的手性自由基具有亲核性，然后被具有完美 1,4-化学选择性和良好立体控制的亲电子氰化物源拦截。