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47.1.1.1.5.2.3 Variation 3: Horner–Emmons and Wittig–Horner Alkenations with Phosphonates and Phosphine Oxides

DOI: 10.1055/sos-SD-047-00004

Schobert, R.; Hölzel, C.; Barnickel, B.Science of Synthesis, (20104764.

Horner couplings of phosphine oxides or phosphonates with aldehydes or ketones have been reported to yield trisubstituted alkenes with high stereoselectivity, especially if either the phosphorus reagent or the carbonyl component bear one large substituent, e.g. a heterocycle. For instance, alkene 134, a key intermediate in the synthesis of phorboxazole A, is obtained in 88% yield and with excellent stereoselectivity (E/Z >95:5) from an α-methyl oxophosphonate and a carbaldehyde (Scheme 46).[‌472‌] Conversely, in syntheses of epothilone A, methyl ketones and α-hetaryl-substituted phosphonates[‌17‌] or phosphine oxides[‌16‌] have been employed to prepare exclusively the E-isomers of the trisubstituted alkenes 135 or 136, respectively (Scheme 46). The HornerEmmons alkenation to produce a trisubstituted E-alkene moiety has even been used as a macrocyclization method in the synthesis of the macrolide antibiotic filipin.[‌473‌]

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M8 M8 M8 Meeee (888M/888M) Meeee (%) Mee
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Meeeeeeeeee 88M

M8 M8 Meeee (%) ee 888 ee ee 888 Meeee (%) ee 888 Mee
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Meeeeeeeeee 88M

M8 M8 ee ee 888M Meeee (%) ee 888M Meeeee (M/M) ee 888 Meeee (%) ee 888 Mee
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8-(Meeeeeeeeeeeeeeeeee)-8-(8-eeeeeeeeeeeeee-8-eeee)-8-eeeeeeeeee-8-ee-8-ee (888); Meeeeee Meeeeeeee:[‌888‌]

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References