Homer-Emmons olefination

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... 

Babler and Schlidt [86] described a route to a versatile C15 phosphonate, used for a stereoselective synthesis of all E retinoic acid and p-carotene. Base-catalyzed isomerization of the vinyl-phosphonate afforded the corresponding allyl-phosphonate as the sole product. Homer-Emmons olefination with ethyl 3-methyl-4-oxo-2-butenoate concluded the facile synthesis of all E ethyl retinoate. The C15 phosphonate was synthesized starting from the epoxide of P-ionone. Subsequent isomerization with MgBr2, afforded the C14 aldehyde in 93%... 

This reaction, known as a Homer-Emmons olefination, was presented to illustrate that through consideration of the electronic nature of a given starting material and the transient species involved in reactions with this material, products of more complex reactions may be identified. However, it is important to note that while this sequence appears complex, each step involved utilizes principles of arrow pushing easily applied from material presented in this book. 

Paulsen, H, Vonde3m, W, Cyclitol reactions 13. S3mthesis of pseudosugars from D-glucose by intramolecular Homer-Emmons olefination, Liebigs Ann. Chem., 2, 125-131, 1987. 

Wittig-Homer-Emmons olefination of serinal derivative l-50 (see Scheme 13.27) with carbonylphosphorane 176 generates enone 177. Subsequent conversion to (—)-nojirimycin l-58 proceeds via anti dihydroxylation and reduction with NaBH4 (Scheme 13.61), whereas reduction with Red-Al leads to (—)-mannonojirimycin [109]. A similar approach has been applied to generate galactostatine [110]. 

Homer-Emmons olefination of 51 with phosphonate 52 followed by brief exposure to acid afforded 53 (67%), which was converted to (+)-calycuhn A and (-)-calyculin B (Scheme 1) ... 

With unfruitful results as shown above, we tried Sutherland s approach for constructing the anhydride segment via Homer-Emmons olefination (50) which was finally chosen in our synthetic study (Scheme 18). In this synthesis, differentiation of the three carboxyl group equivalents in the molecule is required. For this purpose, we planned to employ a condensation between triethyl phosphonoacetate and the a-ketoester 101. 

Wadsworth—Homer—Emmons olefination of aldehyde 464 with glycine phosphonate 571 affords dehydroamino acid 572. The stereochemical outcome of the reaction hinges on the base used for deprotonation. A lithium base such as LDA gives a 1.5 1 mixture of (Z)-572 and the corresponding E isomer (88% yield), whereas a potassium base (potassium r -butoxide) produces only the Z-isomer, in 77% yield [180]. 

Homer-Emmons olefination of 831 provides a,j5-unsaturated ester 845 with high E selectivity. Bases most commonly used to effect the transformation are sodium hydride (for R=CH3) [231] and potassium r butoxide (for R=Et) [232]. Ester 845b is also accessible... 

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 synthesis of (-h )-polyoxamic acid (435), the unusual amino acid component of polyoxin B, incorporates backbone assembly via a Homer- Emmons olefination of L-tartrate-derived aldehyde 430 with (i )-lactate-derived jS-ketophosphonate 914 [101] (Scheme 122). The key introduction of the chiral amine stereocenter is accomplished by a trifluoroacetimidate rearrangement, outlined in Scheme 60 (Section 1.4.7.2). 

The Homer-Emmons olefination shows a preference for the formation of the more stable ( )-olefins. On the other hands. Still and Gennari modified HWE olefination shows high (Z)-stereoselectivity and high yield in the preparation of unsaturated esters, 45(Z) 46( ) = > 50 1, from a variety of aromatic, saturated and unsaturated aliphatic aldehydes. ... 

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