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26.9.1.1.9.1 Variation 1: Wittig Reaction of Oxophosphoranes

DOI: 10.1055/sos-SD-026-00987

Marsden, S. P.Science of Synthesis, (2005261080.

Oxophosphoranes such as 186 are stabilized phosphorus ylides and as such react with aldehydes to deliver enones (e.g., 187) with E stereochemistry (Scheme 36).[‌166‌] The relatively nonbasic nature of the reagents means that sensitive compounds such as those susceptible to racemization are tolerated in either the phosphorane (e.g., 188) or aldehyde (e.g., 189) components.[‌167‌,‌168‌] Ketones are not generally competent partners in intermolecular Wittig reactions with oxophosphoranes, but highly reactive ketones including α-oxo esters (e.g., 190)[‌169‌] and fluorinated ketones[‌170‌] do react in useful yield. Trisubstituted enones can also be accessed by reaction of substituted phosphoranes such as 191 with aldehydes, although the control of the alkene geometry in the resulting enone 192 is not always assured.[‌171‌] Enones (e.g., 193) are prepared directly from activated allylic or benzylic alcohols such as 3-bromoprop-2-en-1-ol by a convenient one-pot oxidation/Wittig protocol using manganese(IV) oxide as oxidant.[‌172‌]

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