Utilisation of CO₂ in the simultaneous installation of the C–C and C═C bonds of α,β-unsaturated carboxylic acids

Development of methods for the conversion of CO₂ (a major waste product) into value-added chemicals has become an area of great interest. Herein we report the development of a new retrosynthetic double disconnection strategy, translating to a highly efficient synthetic methodology in which both the C═C double bond and the C–C bond of an α,β-unsaturated carboxylic acid can be constructed concurrently, with CO₂ as a chemical feedstock. Central to the success of this methodology are “phosphonium carboxylate ylides”. These unique new entities can undergo novel Wittig-type reactions, forming α,β-unsaturated carboxylic acids with excellent stereoselectivity and perfectly regioselective installation of both the carboxyl group and the C═C bond. The α,β-unsaturated carboxylic acid motif appears widely in the structures of pharmaceutical compounds and precursors thereof. The availability of a broadly applicable approach for synthesising α,β-unsaturated carboxylic acids will thus be highly valuable. Surprisingly, this represents the first general direct Wittig-type methodology for formation of the alkene moiety in α,β-unsaturated carboxylic acids.