Phosphoryl carbanions reactions

The simplest application of the Darzens reaction is outlined in Scheme 29. The production of the phosphoryl carbanion has been normally carried out with a metal alkoxide in this respect, r r -butoxide is better than ethoxide, some reactions proceeding only with the former base butyllithium or Ida has also been employed. The carbanion 357 is also available through the chlorination of dialkyl methylphosphonate carbanion with PhSO.CP ... 

The reactions of phosphorylated carbanions have been extended to include those with sulphinate esters as a route to phosphoryl sulphoxides . The interaction of dimethyl... 

The importance of the cation-oxygen interaction has also been pointed out in highly Z-selective olefination reactions of the a-silyl-a-phosphoryl carbanion 19 (Scheme 2.16) [41, 42]. The chelating Li-O interactions are likely to determine the configuration of the carbanion 19 in the approach of the aldehyde. This transition state leads to the formation of the kinetically favored adducts 20, which give the (Z)-alkenes 21 after syn-elimination of the oxophilic silylated moiety and hydrolysis. 

Scheme 2.16. Z-Selective Peterson reaction of an a-silyl-a-phosphoryl carbanion with aldehydes.

An a-phosphoryl sulfoxide (4) has also been prepared by the reaction of the appropriate carbanion with sulfinate ester 19 (see also Section II.A.l)18. Ugi and coworkers prepared (S, R, S)-65 by reaction of (R, R)-64 with ester 19. The (S, S, R) diastereomer was prepared from (S, S)-6496. 

In these a-phosphorylated dithioesters, the electron-withdrawing effect of the phosphono group, which strongly increases the electrophilic character of the thiocarbonyl group, makes the latter more prone to the thiophilic attack of nucleophiles and stabilizes the resulting carbanion. The main reactions of 1 with nucleophiles are summarized in Scheme 2. 

Chlorodiphenylphosphine 488 reacts with a-sulphinyl carbanions to give a-sulphinylphosphines 489 which undergo ready isomerization to a-sulphenylphosphine oxides 4W (equation 295). The report of Almog and Weissman that a-sulphinyl carbanions react with phosphorochloridates 491 to give a-phosphoryl sulphoxides 492 calls for correction (equation 296). Actually, the phosphorylation occurs at the oxygen atom of the ambident dimsyl anion, and is followed by the Pummerer-type reaction affording diethylphosphoric acid and tetraethyl pyrophosphate among other products . ... 

Maryanoff, B.E. and Reitz, A.B. (1989) The Wittig olefination reaction and modifications involving phosphoryl-stabilized carbanions. Stereochemistry, mechanism, and selected synthetic aspects. Chemical Reviews, 89(4), 863-927. 

A convenient route to trivinylphosphine has been developed by thiol elimination from tris[2-(phenylthio)ethyl]phosphine oxide.56 The reaction mechanism involves a phosphoryl-stabilized carbanion, from which benzene thiolate anion is eliminated. 

Not only alky] groups, but also aryl [492, 493], vinyl [494], acyl [276, 495—497], alkoxycarbonyl [498], aminocarbonyl [499-501], silyl [502-504], or phosphoryl groups [279, 280] can migrate to a vicinal carbanion (Scheme 5.68). Because some of these groups can be used to stabilize a-heteroatom-substituted carbanions by chelate formation, migration of these groups to the carbanion is a potential side reaction in the generation and alkylation of chelate-stabilized carbanions. 

The mechanism involves initial formation of an acetylated or phosphorylated cation, which reacts with a carbanion to form a salt that is strongly acidic because of its substituent electron-withdrawing groups. This salt is hence readily converted into an ylide by loss of a proton, whose removal is assisted by the acetic anhydride or triethylamine (see equation 27). As with method B the arsine oxide method is limited to the preparation of stable ylides, since its success depends upon the acidity of the methylene compound. Almost all examples of this method have utilized triphenylarsine oxide tri-w-butylarsine oxide has been used in triethylamine but gave only intractable products in acetic anhydride In a modification of this method, an ylide has been prepared by reaction of acetoacetanilide with diacetoxytriphenylarsorane, the latter compound having been prepared from triphenylarsine and lead tetra-acetate. ... 

The use of anions derived from a phosphine oxide (132) or a diethyl phosphonate (133) to form al-kenes was originally described by Homer.Although these papers laid the foundations for the use of phosphoryl-stabiliz carbanions for alkene synthesis, it was not until Wadsworth and Emmons published a more detailed account of the general applicability of the reaction that phosphonates bet e widely used. Since the work of Wadsworth and Emmons was significant and crucial to the acceptance of this methodology, the reaction of a phosphonate caibanion with a carbonyl derivative to form an alkene is referred to as a Homer-Wadsworth-Emmons reaction (abbreviated HWE). The phosphine oxide variation of the Wittig alkenation is called the Homer reaction. 

A higher yield under similar reaction conditions was observed when a phosphoryl-substituted carbanion reacted with nonsterically hindered methyloxirane to give 2-methylcyclopropane-carboxylic acid (2). ... 

Monosaccharide oxiranes undergo the homo-Horner reaction with phosphoryl-substituted carbanions to give monosaccharides fused with a cyclopropane ring. " a-D-Mannopyrano-side 9, a precursor in an enantiospecific route to (4-)- and ( —)-chrysanthemumdicarboxylic acids, was synthesized in 50% yield by the reaction of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside (8) with ethyl 2-(diethoxyphosphoryl)propanoate. " ... 

Dialkoxyphosphoryl-substituted carbanions, usually generated by the reaction of methyl-substituted phosphonic acid dialkyl esters with sodium hydride, react with a variety of oxiranes to give substituted cyclopropanes in moderate to good yield. Whereas the reaction of A5-phos-phanes with oxiranes (see Section 1.2.2.1.) gives cyclopropanes under forcing reaction conditions (200 °C, 8 hours), the phosphoryl-substituted carbanions give cyclopropanes under relatively mild conditions by a similar reaction mechanism (Houben-Weyl, Vol4/3, p 138). 

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