Organocatalytic Deoxygenative Reduction of α,β-Unsaturated Ketones.

The development of chemoselective reduction methods for conjugated carbonyl compounds remains a long-standing challenge in organic synthesis. Here we introduce a metal-free organocatalytic strategy that accomplishes the deoxygenative reduction of α,β-unsaturated ketones through the distinct FLP-type reactivity of N-heterocyclic nitrenium (NHN) salts and their N-H triazane derivatives. The protocol operates efficiently with low catalyst loadings, accommodates diverse substrates, and can be scaled to gram quantities. Key to the selectivity is the transient use of water or methanol as a protecting agent for the C═C bond, enabling targeted carbonyl reduction by hydride transfer from triazane. Combined experimental and computational studies elucidate the origins of chemoselectivity and reveal how hydride affinity and ion pairing distinguish NHN-based catalysis from B(C6F5)3-mediated reductions. These findings expand the synthetic toolbox for selective enone deoxygenation and establish nitrenium FLP chemistry as a promising platform for the design of new, metal-free reduction processes.