Wittig synthesis review

For a review of these double ring closures, see Vollhardt, K.P.C. Synthesis, 1975, 765. For a review of applications of the Wittig reaction to the synthesis of natural products, see Bestmann, H.J. Vostrowsky, O. Ref. 722. 

Carbonyls. The stereochemistry of the Wittig olefin synthesis has been reviewed. /i-a/u-Stereoselective olefin synthesis via /3-oxido-ylides is possible only in the presence of soluble lithium salts. Protonation of jS-oxido-ylides prepared from salt-free ylides leads to mixtures of erythro-and r/jr o-betaines and hence to mixtures of cis- and rm/i5-olefins. 

A recent review on four-membered heterocycles formed from imino-phosphoranes concentrates on the preparation and the reactivity of 2,4-diimino-l,3-diazetidine and related compounds (93JPR305). As an example, the synthesis via bisiminophosphorane 85 is described in Scheme 42. The bisiminophosphorane has both a heteroaryl and a styryl site. From a mechanistic view, the reaction of the bisiminophosphorane proceeds with aryl isocyanate formation via an aza-Wittig mechanism. Intermediate car-bodiimide formation (86) occurs directly on the iminophosphorane moiety... 

Although this review is by no means exhaustive, it should present an impression of the importance of iminophosphoranes as versatile synthons in heterocyclic synthesis. Much attention was paid to the aza-Wittig reaction, which enables the preparation of a wide range of simple and complex heterocyclic systems. 

For a review of applications of the Wittig reaction to the synthesis of natural products, see Bestmann Vostrowsky, Ref. 638. 

Although the methods reviewed above have been most widely used for synthesis of conducting polymers, there are many other organic reactions capable of producing conjugated structures. One example is the Wittig condensation of bis-triphenyl-phosphonium compounds with dialdehydes in the presence of a strong base, typified by the synthesis of poly(p-phenylene-vinylene) 102). 

The Wittig and related reactions have been reviewed in the context of natural product synthesis 120 mechanistic studies of the Wittig reaction have also been reviewed with particular reference to asymmetric induction.121... 

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... 

A review which describes recent developments of the aza-Wittig rearrangement and its application in alkaloid synthesis has appeared.212 The aza-[2,3]-Wittig rearrangement (157) (158) has been shown to be accelerated by the incorporation of certain... 

Similarly, the acid hydrolysis of (3-lactam 7 has been described [55] to give the a-hydroxy (3-amino acid 8, a suggested /V-temiinal component of angiotensinconverting enzyme inhibitor microginin 4, Scheme 2. The key precursor 7 was obtained through a Wittig olefination of the 4-formyl (3-lactam 5, followed by simple elaboration of the resulting 6 (for a review on the use of 4—formyl (3-lactams in synthesis, see [56]). 

In the present review the ring systems containing one heteroatom are considered first, except for P-lactams which are given a special section at the end. Interest in azetidines continues to be stimulated by the discovery of the potentially useful trinitro derivative. The requirements for the stereoselective synthesis of substituted oxetane are being explored and derivatives of aluminium are useful in the stereoselective routes to oxetanones. The preparation and subsequent pyrolysis of oxetanones is suggested as an alternative to the Wittig route to olefins. Stereoselective routes to thietanes and thietane 1 -oxides are mentioned. 

A major review on the synthesis and chemistry of 1,4-, 4,1-, and 1,5-benzoxazepines, covering the literature to the end of 2000, was published [01JHC1011]. The use of domino Wittig-pericyclic reactions in the synthesis of a range of bioactive heterocycles including 7-membered rings has also been reviewed [02MI1181],... 

Review articles on carbodiimides were published by Khorana in 1953, by Kurzer and Douraghi-Zadeh in 1967, byMikolajczykandKielbasinski in 1981 and by Williams and Ibrahim in 1981. Carbodiimides containing silicon, germanium, tin and lead substituents were reviewed by Gordetsov and coworkers in 1982, N-functionalized carbodiimides by Vovk and Samarai in 1992 and polycarbodiimides by Pankratov in 1993. A review on the synthesis of heterocycles by the aza-Wittig reaction appeared in 1991. ... 

The Wittig alkenation has found widespread application in synthetic organic chemistry, and numerous papers and reviews have detailed the progress of the Wittig reaction. A principal advantage of alkene synthesis by the Wittig reaction is that the location of the double bond is absolutely fixed in contrast to the mixture often produced by alcohol dehydration. With simple substituted ylides Z-alkenes are favoured. 

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. ... 

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