Emmons

The reaction has been extended to include carbanions generated from phosphonates. This is often referred to as the Horner-Wittig or Homer-Emmons reaction. The Horner-Emmons reaction has a number of advantages over the conventional Wittig reaction. It occurs with a wider variety of aldehydes and ketones under relatively mild conditions as a result of the higher nucleophilicity of the phosphonate carbanions. The separation of the olefinic product is easier due to the aqueous solubility of the phosphate by-product, and the phosphonates are readily available from the Arbusov reaction. Furthermore, although the reaction itself is not stereospecific, the majority favor the formation of the trans olefin and many produce the trans isomer as the sole product. 

Triethylphosphonoacetic acid [867-13-0] (PEPA) is a useful olefination reagent for Homer-Emmons reactions in organic synthesis. 

Other approaches to direct C2Q couplings have been reported (9,30—35). Based on their knowledge of sulfone chemistry, Rhc ne-Poulenc has patented many syntheses of P-carotene which use this olefination chemistry (36—41). Homer-Emmons chemistry has also been employed for this purpose (42). The synthetic approaches to the carotenoids have been reviewed (43). 

Homofolic acid, 5,11-methenyl-tetrahydro-biological activity, 3, 327 Homofolic acid, tetrahydro-biological activity, 3, 327 Homoisoflavanones occurrence, 3, 722 thermoisomerization, 3, 722 thermolysis, 3, 728 Homolytic reactions heterocyclic compounds reviews, 1, 74 Homophthalic acid isocoumarins synthesis from, 3, 830 synthesis, 3, 830 Homophthalic anhydride isochroman-l-one synthesis from, 3, 860 20a-Homoporphyrin nomenclature, 1, 30 Homopterocarpin isolation, 4, 998 ( )- D- Homotestosterone synthesis, 1, 453 Homer-Emmons reaction chromene synthesis by, 3, 749 Hortiacine isolation, 3, 149 Hortiamine isolation, 3, 149... 

Wadsworth-Emmons reactions crown ethers and, 7, 759 Warfarin... 

HORNER - WADSWORTH - EMMONS Olelination Wittig type reaction of ptwsptionale stabilized carbanions with aldehydes or ketones to form olefins... 

Miller, H. and H. Emmons, 1981, Documentation for CFCV, the Fifth Harvard Computer Fire Code, Harvard University, Cambridge, MA, October. 

The direct reduction of esters with diisobuty laluminum hydride in the presence of the Horner-Emmons reagent prepared from ethyl diethylphosphon-ofluoroacetate avoids the necessity to work with sensitive aldehydes in the olefi-nation procedure [72, 75] (equation 62) (Table 23). 

Trapping of the same Homer-Emmons reagent with an acid chloride leads to the formation of the a-fluaro- -keto esters in good yields [74] (equation 63) (Table 24)... 

Homer-Emmons reagents react with trifluoromethyl ketones to form tnfluo romethylated olefins, however, the double bond can isomerize out of conjugation with the carboxylic acid group with the product olefin that bears a y-proton [37] (equation 30)... 

The only computational approach found in the literature to modeling flash-hre radiation is that of Raj and Emmons (1975), who modeled a flash fire as a two-dimensional, turbulent flame propagating at a constant speed. The model is based on the following experimental observations ... 

Because the Raj and Emmons (1975) expression for tv cannot be applied in a straightforward manner, the expression given here differs from that recommended by Raj and Emmons (1975). It should be emphasized that w, which represents the inverse of the volumetric expansion due to combustion in the plume, is highly... 

The model gives no solution for the dynamics of a flash fire, and requires an input value for the burning speed S. From a few experimental observations, Raj and Emmons (1975) found that burning speed was roughly proportional to ambient wind speed U ... 

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