2- phosphoranes

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

Surprisingly carbonyl-substituted carbanions of phosphonates, in which the negative charge is delocalized over two oxygen atoms, are much more nucleophilic than the corresponding phosphoranes. This effea has first been observed by Homer, and has often been utilized in the synthesis of acylated olefins (R.D. Clark, 1975). 

In a similar way the use of the 2-methyl-3-isothiocyanato-4-thiocyanato-hept-3-ene (252) prepared from thiocyanogen and the oxoal-kylene phosphorane (251) yields the 2-anilino-4-propyl-5-isopropyl-thiazole (253) by condensation with aniline (Scheme 128). 

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.. 

Extension of the Phosphorane Route. Ample evidence of the versatihty of the phosphorane synthesis strategy is provided by the proliferation of penems that followed. Nucleophilic displacement of the acetate function of the acetoxy-azetidinone (51, R = OCOCH ) [28562-53-0] (86) provided azetidinones where R = SCOCH, SCSSC2H, and SCSOC2H, which on elaboration gave the penems (52, R = CH ) (87), (52, R = SC2H ) (88), (52, R = 0C2H ) (89). Similar treatment of 3-substituted (or disubstituted) acetoxyazetidinones allowed the synthesis of a number of 2-substituted- 6-alkyl-and 6,6-dialkylpenems (90). 

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... 

Polythia six-membered ring systems, 3, 1039-1086 Polythiazides as diuretic, 1, 174 Polythiiranes, 7, 182 Polytopal rearrangements phosphoranes, 1, 529-530 rules, 1, 530 Polyurethanes curing agents... 

Olmethyl-3-methoxy-3-phenyl-l-(2,6-dimethyiphenyi)-lH>lmldazo(l,2 b) pyrrazol-2(3H)-one (3) Phosphorane 2 (t 48 g 3 mmol) and 2 6 dimethylphenylisocya-nate 3 (0 59 g 4 mmol) in PhMe (30 mL) was heated under reflux with stimng for 16 h (TLC EtOAc hexane I 6) Evaporation and column chromatography (silica gel EtOAc/hexane 1 6) afforded crude 4 Recrysiallization from EtaO petroleum ether gave 0 930 g (66%) mp 126 5 130"C... 

Olefin synthesis Irom phosphorane ylides (e g 3) with aldehydes or ketones cis olelins predominate in aliphatic systems trans m coniugated olefins... 

Ethyl (triphenylphosphoranylidene)acetate is available from FIuka AG and Trldom Chemical Inc. under the name (ethoxycarbonylmethylene)triphenyl-phosphorane and from Aldrich Chemical Company, Inc. under the name (carbethoxymethylene)triphenylphosphorane. The reagent may be prepared from triphenyl phosphine and ethyl bromoacetate by the following procedure. ... 

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. 

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