Proline-promoted electrophilic dichloromethylation of α-enaminones via stereochemically gated resolution.

Abstract

The direct incorporation of polyhalomethyl groups into carbonyl frameworks has traditionally relied on radical or carbene intermediates. Here, we report a proline-mediated, closed-shell strategy for electrophilic β-polyhalomethylation of α-enaminones using stable haloforms under mild, metal-free conditions. The reaction proceeds with high diastereoselectivity, governed by a stereoelectronic gating mechanism that links molecular topology to productive C-C bond formation. The platform accommodates a broad range of CX₂ donors, including CHBr₃, CHBr₂Cl, and CBrCl₃, and reveals topology-dependent divergence: six-membered α-enaminones yield isolable β-functionalized products, while five-membered analogs engage in a spontaneous cascade, triggered by reaction with proline, culminating in aromatized benzenoid scaffolds. Structural, isotopic, and spectroscopic studies support a unique reactivity manifold defined by polarity inversion and closed-shell transfer. This work redefines electrophilic halomethane chemistry, establishes a mechanistic class for β-functionalization, and positions α-enaminones as versatile, programmable platforms for topology-driven reactivity and downstream synthetic elaboration.