Wadsworth—Emmons olefination = Horner

Related reactions Horner-Wadsworth-Emmons olefination, Horner-Wadsworth-Emmons olefination - Still-Gennari modification,... 

Related reactions Homer-Wadsworth-Emmons olefination, Horner-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Peterson olefination, Takai-Utimoto olefination, Tebbe olefination, Wittig reaction - Schlosser modification ... 

Scheme 21 Higher order Horner-Wadsworth-Emmons olefination via hexacoordinated intermediates 67...

Similarly, starting from 2,3 5,6-di-0-isopropylidene-D-mannofuranose 72, a one-pot procedure that implies the synthesis of glycosyl sulfones by Horner-Wadsworth-Emmons olefination with phosphonate 73, followed by subsequent Michael addition and Ramberg-Backlund reaction92 gives compound 74 in 78% yield93 (Scheme 24). 

In a different approach, Franck-Neumann et al. [24] utilized the manganese complex 14 (formed by deracemization) to obtain the enantiomerically pure target molecule 12 via Horner-Wadsworth-Emmons olefination and oxidative decomplexation of the intermediate vinylallene complex 15 (Scheme 18.6). 

Syntheses follow a kind of bio-mimetic approach [283, 284] in building up the chain during a sequence of Wittig-type reactions or Horner-Wadsworth-Emmons olefination, adding two carbons to the chain at a time with either methyl- or ethyl-branches. As the final products need to be highly pure (E)-stereoisomers, reaction steps and purification need to be carefully controlled. 

Synthesis of a C(8)-C(18) segment of the larger fragment of lb using the same basic strategy is depicted in Scheme 25. Here, hydroxy ketone 176 was subjected to syn-selective (dr of crude product=90 10) reductive amination [42] with sodium cyanoborohydride and benzylamine followed by tetrahydro-oxazine formation using aqueous formaldehyde. The resulting heterocycle 182 was then converted to unsaturated ester 184 by successive desilylation, oxidation, and entirely (Z)-selective Horner-Wadsworth-Emmons olefination. Re-... 

Epimerizable aldehydes clearly undergo intermolecular Horner-Wadsworth-Emmons olefination with trimethyl phosphonoacetate, by using the weak base, lithium hexaflu-oroisopropoxide [LiOCH(CF3)2], as catalyst.203... 

The enoates 17 were obtained in good yield and diastereoselectivity by subjecting the crude hydroformylation products 6 to Horner-Wadsworth-Emmons olefination conditions (HWE). Reaction of enoates 17 with dialkyl Gilman cuprates gave the anti 1,4-addition... 

Fig. 11.28. Aldehyde alkyne chain elongation via [1 -rearrangement of a vinyl carbene (Seyferth procedure). First, a Horner-Wadsworth-Emmons olefination of the aldehyde is carried out to prepare alkene A. Upon warming to room temperature, alkene A decomposes and gives the vinyl carbene B. From that, the alkyne is formed by way of a [1,2]-rearrangement.

HORNER-WADSWORTH-EMMONS OLEFINATION - STILL-GENNARI MODIFICATION... 

Horner-Wadsworth-Emmons Olefination (Still-Gennari modification) 214... 

Pihko, P. M., Sale, T. M. Excess sodium ions improve Z selectivity in Horner-Wadsworth-Emmons olefinations with the Ando phosphonate. Tetrahedron Lett. 2003, 44,4361-4364. 

Janecki, T., Bodalski, R., Wieczorek, M., and Bujacz, G., Horner-Wadsworth-Emmons olefination of nonstabilized phosphonates. A new synthetic approach to P.y-unsaturated amides, Tetrahedron, 51, 1721, 1995. 

The synthesis of the Cl-Cl5 segment (116) [198] of streptovaricin D (109) has been carried out from the aldehyde (115) [199], an enantiomer of an intermediate used by the same authors in the synthesis of the rifamycin ansa chain. Compound (105) was submitted to the Evans aldol procedure to give an aldol, which was transformed into the corresponding acetonide. Ozonolysis to the expected aldehyde and crotylmetallation with chromium(II) chloride provided a 5 1 mixture of diastereoisomers. The major component was acylated, giving only one diastereoisomer after ozonolysis and crotylboration. Final introduction of the corresponding (2 ,4Z)-dienoate unit by two subsequent Horner-Wadsworth-Emmons olefinations afforded compound (116) (Scheme 51). 

Y = PR3j. Wittig, Horner, Wadsworth- Emmons olefinations OK ... 

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