Phosphoranes reaction

Spirobicyclic phosphoranes, reaction with hex-afluoroacetone, 30 236 Spirobicyclotriphosphazene, 21 110 Spirocyelic phosphoranes, 30 245 square-planar structure, 30 248 synthesis, 30 252... 

The first synthesis of 289 and 290 started from the base-catalyzed addition of a sugar containing an isolated hydroxyl group to 2,7-dimethyl-3,5-octa-dyine-2,7-diol (286). Two enynyl ethers (287 and 288) were formed and separated, the partial hydrogenation over a Lindlar catalyst affording dienyl ethers 289 and 290. Alternatively, both ethers were prepared by a Wittig reaction from chloromethyl ether (291) a phosphonium salt (292) was prepared and converted into a phosphorane. Reaction with acrylaldehyde gave a mixture of 289 and 290. 

Wittig reaction The reaction between an alkyl-idene phosphorane, C = PR3 and an... 

Synthesis. The first hiUy alkyl/aryl-substituted polymers were reported in 1980 via a condensation—polymeri2ation route. The method involves, first, the synthesis of organophosphine-containing alkyl or aryl substituents, followed by the ready oxidation of the phosphine to a phosphorane with leaving groups suitable for a 1,2-elimination reaction. This phosphorane is then thermally condensed to polymers in which all phosphoms atoms bear alkyl or aryl substituents. This condensation synthesis is depicted in Eigure 2 (5—7,64). 

The racemic form of the unsubstituted nucleus (1, X = CH2) was synthesized by several groups (32—34) prior to the disclosure of the natural material. One reaction path involved an azetidinone (21) where R = CH2OH or CH=CH2 converted to the corresponding phosphorane (22) where R = o-NO.-C,H, when R = CH.OH and R = COCH, when R=CH=CH.. 

A variety of 1-azirines are available (40-90%) from the thermally induced extrusion (>100 °C) of triphenylphosphine oxide from oxazaphospholines (388) (or their acyclic betaine equivalents), which are accessible through 1,3-dipolar cycloaddition of nitrile oxides (389) to alkylidenephosphoranes (390) (66AG(E)1039). Frequently, the isomeric ketenimines (391) are isolated as by-products. The presence of electron withdrawing functionality in either or both of the addition components can influence the course of the reaction. For example, addition of benzonitrile oxide to the phosphorane ester (390 = C02Et) at... 

Phosphonium hexafluorophosphate, benzotriazolyl-N-hydroxytris(dimethylamino)-in peptide synthesis, 5, 728 Phosphonium salts chromene synthesis from, 3, 753 reactions, 1, 531 Phosphonium salts, vinyl-in pyrrole synthesis, 4, 343 Phosphonium ylides in heterocyclic synthesis, 5, 165 Phosphoramide, triethylene-as pharmaceutical, 1, 157 Phosphoramide, triethylenethio-as pharmaceutical, 1, 157 Phosphorane, pentaphenyl-synthesis, 1, 532 Phosphoranes, 1, 527-537 Berry pseudorotation, 1, 529 bonding, 1, 528... 

The acylation of Wittig reagents provides the most convenient means for the preparation of allenes substituted with various electron-withdrawing substituents. The preparation of o-allenic esters has been accomplished by the reaction of resonance-stabilized phosphoranes with isolable ketenes and ketene itself and with acid chlorides in the presence of a second equivalent of the phosphorane. The disadvantages of the first method are the necessity of preparing the ketene and the fact that the highly reactive mono-substituted ketenes evidently cannot be used. The second method fails when the a-carbon... 

The reaction times varied from 10 min to 18 hr. A=the correspondi ng phosphonii salt was used with the addition of two moles of triethyl amine. B=the corresponding phosphorane was used with the addition of one mole of triethylamine. 

The submitters have shown that these reactions proceed by dehydro-chlorination of the acid chloride to the ketene, which is then trapped by reaction with the phosphorane. The resulting betaine decomposes to the allenic ester via an oxaphosphetane. In contrast, the reaction of acid chlorides with 2 equivalents of phosphoranes involves initial acylation of the phosphorane followed by proton elimination from the phosphonium salt. ... 

Bis(tnfluoromethyl -substituted phosphoranes are obtained on reaction of bis(tnfluoromethyl)-substituted heterodienes and P(ni) species [74J, 742 143] In the case of sulfur- and selemum-contaimng phosphoranes, the corresponding heterodienes are generated in situ from heterocyclic precursors [137] (equation 32)... 

Nonclassical Wittig reaction, olefination by phosphoranes interaction with carboxylic acid derivatives, in transformation of heterocycles 99JCS(P1)3049. 

The reaction of an alkylidene phosphorane 1 (i.e. a phosphorus ylide) with an aldehyde or ketone 2 to yield an alkene 3 (i.e. an olefin) and a phosphine oxide 4, is called the Wittig reaction or Wittig olefination reaction. ... 

In the following procedure, use is made of the basic character of epoxides. In the presence of phosphonium salts, ethylene oxide removes hydrogen halide and the alkylidenetriphenylphosphorane is produced. If a suitable carbonyl compound is present in the reaction mixture, its reaction with the in situ generated phosphorane proceeds readily to give the Wittig product. 

The teal value of the Wittig reaction is that it yields a pure alkene of defined structure. The C=C bond in the product is always exactly where the OO group was in the reactant, and no alkene isomers (except E,Z isomers) are formed. For example, Wittig reaction of cyclohexanone with methylenetriphenyl-phosphorane yields only the single alkene product methylenecyclohexane. By contrast, addition of methylmagnesium bromide to cyclohexanone, followed by dehydration with POCI3, yields a roughly 9 1 mixture of two alkenes. 

Ylide (Section 19.11) A neutral dipolar molecule with adjacent positive and negative charges. The phosphoranes used in Wittig reactions are ylides. 

Triphenylphosphine, in preparation of dichloromethylenetriphenyl-phosphorane, 46, 33 reaction with N,N-dimethylamino-benzaldehyde to yield /9,0-di-chloro-p-dimethylaminostyrene, 46,33... 

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

In the Wittig reaction an aldehyde or ketone is treated with a phosphorus ylid (also called a phosphorane) to give an alkene. Phosphorus ylids are usually prepared by treatment of a phosphonium salt with a base, and phosphonium salts are usually prepared from the phosphine and an alkyl halide (10-44) ... 

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