Wittig rearrangement alkene synthesis

Snider and colleagues have developed the sequential ene reaction/thia-[2,3]-Wittig reaction which provide appropriately functionalized product 152 at allylic position on simple alkene 150 in two steps involving intermediate 151 (equation 87) . Thia-[2,3]-Wittig rearrangement was often utilized as a key step of natural product synthesis. Masaki and colleagues have demonstrated that the potassium enolate thia-[2,3]-rearrangement of aUyl sulfide 153 to 154 is useful for the synthesis of terpenoid diol component 155 of the pheromonal secretion of the queen butterfly (equation 88) . 

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

Z)-Trisubstitutedalkenes. Still and Mitra have described an efficient synthesis of alkenes of this type from allylic alcohols by a [2.3] sigmatropic Wittig rearrangement. The alcohol 2 is converted into the allyl stannylmethyl ether (3), which can be isolated if desired. Treatment with n-butyllithium results in tin-lithium exchange and rearrangement to the homoallylic alcohol 4 in 95% overall yield. When 3 is transmetalated and immediately quenched with cyclohexanone, 5 is obtained in 73% yield. 

Both intermolecular and intramolecular additions of carbon radicals to alkenes and alkynes continue to be a widely investigated method for carbon-carbon bond formation and has been the subject of a number of review articles. In particular, the inter- and intra-molecular additions of vinyl, heteroatomic and metal-centred radicals to alkynes have been reported and also the factors which influence the addition reactions of carbon radicals to unsaturated carbon-carbon bonds. The stereochemical outcome of such additions continues to attract interest. The generation and use of alkoxy radicals in both asymmetric cyclizations and skeletal rearrangements has been reviewed and the use of fi ee radical reactions in the stereoselective synthesis of a-amino acid derivatives has appeared in two reports." The stereochemical features and synthetic potential of the [1,2]-Wittig rearrangement has also been reviewed. In addition, a review of some recent applications of free radical chain reactions in organic and polymer synthesis has appeared. The effect of solvent upon the reactions of neutral fi ee radicals has also recently been reviewed. ... 

A [2,3]- Wittig rearrangement carried out on a carbohydrate template has been used in a route to 3-alkyl malic acids, as indicated in Scheme 24. The product of opposite chirality at C-3 could be obtained from the cis-alkene, and transition-state models were proposed to rationalize the results.93 Somewhat similar intermediates were used in a synthesis of the stereospecifically-deuteriated ester (llO), required as a standard in a study of enzyme stereospeciflcity in this case C-3 of D-glucose became C-1 of the carbojqrlic acid by oxidative cleavage.94... 

X.J. Wang, S.A. Hart, B. Xu, M.D. Mason, J.R. Goodell, F.A. Etzkorn, Serine-c/s-proline and Serine-frans-proline isosteres Stereoselective synthesis of (Z)- and ( )-alkene mimics by still-wittig and ireland-claisen rearrangements, J. Org. Chem. 

We have expanded our collection of stereoselective reactions even more in the making of alkenes by the Wittig reaction (chapter 15), from acetylenes (chapter 16), by thermodynamic control in enone synthesis (chapters 18 and 19) and in sigmatropic rearrangements (chapter 35). We have seen that such E- or Z-alkenes can be transformed into three-dimensional stereochemistry by the Diels-Alder reaction (chapter 17), by electrophilic addition (chapters 23 and 30), by carbene insertion (chapter 30) and by cycloadditions to make four-membered rings (chapters 32 and 33). 

Epoxide formation (path c) is an important side reaction which can become the dominant pathway. For example, the addition of sulfur ylides to ketones (equation 2) constitutes a general synthesis of epoxides, while 2-hydroxy sulfides undergo the semipinacol rearrangement under certain conditions (equation 3). Elimination (path d) is observed in some special cases such as 2-hydroxy si lanes (1 X = SiR.i the Peterson alkenation)" and 2-hydroxyphosphonium species (1 X = PRs" " Wittig intermediates). ... 

This approach has been applied to the synthesis of peptide isosteres, compounds that have the same shape as peptides but lack the amide link. In this case 99 it is replaced by an E-alkene. The starting material 97 is made from the natural amino acid leucine and the Wittig-Still [2,3] shift on 98 rearranges this into an E-alkene flanked by two chiral centres 99. 

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