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26.9.1.1.9.3 Variation 3: Horner–Wadsworth–Emmons Reaction

DOI: 10.1055/sos-SD-026-00987

Marsden, S. P.Science of Synthesis, (2005261082.

The HornerWadsworthEmmons reaction of oxophosphonate anions with aldehydes generates E-enones. Generally the sodium salts of the oxophosphonates are used, and stereoselectivity is normally good. The reaction has been widely used in the synthesis of side chains for prostaglandins[‌176‌] and thromboxanes,[‌177‌] as exemplified by the formation of 201 by the condensation of aldehyde 199 with oxophosphonate 200 (Scheme 39). The reactions can also be used to form sensitive polyenones with good levels of stereocontrol by condensation with unsaturated aldehydes.[‌178‌] Thus, trienedione 204 is formed as the all-E-isomer by condensation of the anion of 202 with dienal 203, whereas the use of Z-enal 205 yields the E,Z-isomer 206. Ketones, although much less reactive partners than aldehydes, can also be used as substrates for the reactions, yielding trisubstituted enones such as 207.[‌179‌] As usual for the HornerWadsworthEmmons reactions, where base-sensitive oxophosphonates and/or aldehydes are used, the mild conditions, introduced by Masamune and Roush, using lithium chloride and amine bases deliver superior results.[‌180‌] As an example of this, phosphonate 208 is prone to racemization and aldehyde 209 to base-mediated self-condensation. Attempted reactions using stronger bases has limited success but the new conditions give good yields of enone 210 with no loss of stereochemical integrity.

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