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DOI: 10.1055/sos-SD-020-01227

Vanderwal, C. D.; Jacobsen, E. N.Science of Synthesis, (2007201322.

The HornerWittig reaction, in which the phosphine oxide functional group serves as a carbanion-stabilizing group before ultimately suffering elimination, is not used as often for the introduction of the alk-2-enoic acid ester function as its phosphorane and phosphonate counterparts. This is perhaps because the development of general and geometrically selective methods for the HornerWittig reaction has not been as successful as in the case of the Wittig and HornerWadsworthEmmons reactions. Nonetheless, this is a viable method for accessing alk-2-enoic acid esters by homologation of carbonyl compounds, and good geometrical selectivity can be obtained in certain cases.[‌58‌] Examples of selective reactions are given in Scheme 18; unsaturated aldehyde 94 is converted into ester 95 with 9:1 E/Z selectivity, and aldehyde 96 is transformed into trisubstituted alk-2-enoic acid ester 97 with near perfect E-isomer selectivity.

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