Olefination of aldehydes with alpha-halo redox-active esters

Olefin synthesis is a fundamentally important process in organic chemistry. Among the numerous approaches to obtaining olefins such as alcohol/halide eliminations, alkyne-based reductions and additions, pericyclic reactions, metal-mediated cross-couplings, olefin metathesis, etc., carbonyl olefinations are particularly of significance, as exemplified by the Wittig-type reactions. In this report, we describe a new decarboxylative carbonyl olefination in one step with a broad substrate scope under mild conditions by merging an aldehyde and the α-halo carboxylic N-hydroxyphthalimide (NHPI) ester. Mechanistic investigations reveal that this reaction takes place via a tandem nucleophilic addition/reductive E1cb process. The operational simplicity, the ready availability of both starting materials and the versatility of the olefin product demonstrate the potential synthetic utility of this decarboxylative carbonyl olefination.