Homer-Emmons reagent

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 Homer - Emmons reagent (52) is effective in the one carbon homologation of ketones possessing acidic a-hydrogen atoms <96SL875> and electron-deficient alkenes add to 2-phenylseleno-l,3-dithiane in a photo-initiated heteroatom stabilised radical atom transfer process, giving products of considerable synthetic potential <96TL2743>. 

The Homer-Emmons addition of dialkyl carboalkoxymethylenephosphonates to aldehydes [22] has been widely used to generate a,p-unsaturated esters which, in turn, can be reduced to allylic alcohols. Under the original conditions of the Homer-Emmons reaction, the stereochemistry of the oc,(3-unsaturated ester is predominantly trans and therefore the trans allylic alcohol is obtained upon reduction. Still and Gennari have introduced an important modification of the Homer-Emmons reaction, which shifts the stereochemistry of the a,[i-unsaturated ester to predominantly cis [23], Diisobutylaluminum hydride (DIBAL) has frequently been used for reduction of the alkoxycarbonyl to the primary alcohol functionality. The aldehyde needed for reaction with the Homer-Emmons reagent may be derived via Swern oxidation [24] of a primary alcohol. The net result is that one frequently sees the reaction sequence shown in Eq. 6A. 1 used for the net preparation of 3E and 3Z allylic alcohols. 

Ando, K., Practical synthesis of Z-unsaturated esters by using a new Homer-Emmons reagent, ethyl diphenylphosphonoacetate. Tetrahedron Lett., 36, 4105, 1995. 

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

Sharpless and Masumune have applied the AE reaction on chiral allylic alcohols to prepare all 8 of the L-hexoses. ° AE reaction on allylic alcohol 52 provides the epoxy alcohol 53 in 92% yield and in >95% ee. Base catalyze Payne rearrangement followed by ring opening with phenyl thiolate provides diol 54. Protection of the diol is followed by oxidation of the sulfide to the sulfoxide via m-CPBA, Pummerer rearrangement to give the gm-acetoxy sulfide intermediate and finally reduction using Dibal to yield the desired aldehyde 56. Homer-Emmons olefination followed by reduction sets up the second substrate for the AE reaction. The AE reaction on optically active 57 is reagent... 

Wittig/Homer-Wadsworth-Emmons reagents on a PEG support (Table 8, entry 25) [477] ... 

Kann, N., Rein, T.. Akermark. B., and Helquist, P., New functionalized Homer-Wadsworth-Emmons reagents. Useful building blocks in the synthesis of polyunsaturated aldehydes. A short synthesis of ( )-( , )-coriolic acid.. 1. Org. Chem., 55, 5312, 1990. 

Bodalski, R., Pietrusiewicz, K.M., Monkiewicz, J., and Koszuk, J., A new efficient synthesis of substituted Nazarov reagents. A Wittig-Homer-Emmons approach. Tetrahedron Lett., 21, 2287, 1980. 

The transformation outlined in Scheme 14 nicely illustrates some of the advantages associated with the Peterson alkenation relative to the Homer-Emmons reaction for the conversion of the aldehyde (31) into the a,3-unsaturated aldehyde (32). When the corresponding phosphonate reagent is used, only the 3-hy-droxy phosphonate (33) is isolated elimination to form the a,3-unsaturated imine from (33) could not be induced under a variety of conditions. ... 

The Homer—Emmons reaction can be tuned to favor the formation of Z- olefin by using bis(2,2,2-trifluoroethyl)carboxymethyl phosphonate (848), a reagent developed by Clark Still. Consequently, olefination of 847 with 848 gives , Z-diene ester 849 with 15 1 selectivity... 

A short synthesis of (+ )-angelica lactone (260) takes advantage of Homer—Emmons olefination of 831 with the Still reagent (848 Scheme 113) to give (Z)-a,j -unsaturated ester 869 in high yield and geometric purity. Removal of the THP group under mild acidic conditions furnishes the (5 S)-butenolide 260 [133]. 

The Homer-Emmons modification uses a phosphonate-stabilized carbanion in a Wittig reaction. This reagent is an anion that is more nucleophilic than the usual Wittig ylide. The byproduct (R0)2P02 is water-soluble and easily separated from the product. These phosphonate-stabilized carbanions are compatible with carbonyl groups (especially esters) in the reagent. 

The addition of highly basic NaOt-Bu to chiral aluminium(m) lithium(i) bis(binaphtholate) 70 was also effective, and the enantioselective Michael reaction of cyclic enones with Homer-Wadswoth-Emmons reagents, such as 71, proceeded at room temperature (Scheme 2.41). Complex 70 itself did not promote the reaction even at 50 °C. 

Muscone (40) is a sex pheromone of the musk deer and a chemical component of cosmetics. A 12-member library of racemic muscone analogs was synthesized by Nicolaou et al.," who anployed a cyclorelease method on solid support to form the macrocycle scaffold (Figure 11.17). A phosphonate-functionalized resin loaded on encoded SMART microreactors 36 was coupled to olelinic esters 35 to form the p-ketophosphonates 37. Sorting and cross olefin metathesis of 37 with two alkenols followed by oxidation with Dess-Martin reagent gave aldehydes 38. An intramolecular ketophosphonate-aldehyde condensation (Homer-Emmons-Wadsworth reaction) of 38 caused smooth cyclorelease of macrocyclic enones 39. Parallel solution-phase chemistry completed the sequence. 

A modified Homer-Wadsworth-Emmons reagent with high Z stereoseiectivity using trifluoroethyl phosphonates in reaction with saturated, unsaturated or aromatic aldehydes. 

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