Phosphonium methylide

Diazolo[5,l-c][l,2,4]triazines 239 were prepared (81JHC675) by cycliz-ing diazoazoles 236 with acetyltriphenyl-phosphonium methylides. The latter behave as phosphonium enolates 237, l-nucleophile-2-electrophiles, rather than the respective tautomers that behave as 1-nucleophile-1-electrophiles. The cyclocondensation was suggested to involve betaines... 

The cychc gold(I) phosphonium methylide heterocycles are the precursors for the few organogold(II) species reported. Oxidative addition (see Oxidative Addition) of halogen and alkyl halides leads to bicyclic compounds containing a transaimular Au Au bond (equations 28 and 29). These reactions are surprisingly facile and are now known to be... 

Volatron, F., Eisenstein, O. Wittig versus Corey-Chaykovsky Reaction. Theoretical study of the reactivity of phosphonium methylide and sulfonium methylide with formaldehyde. J. Am. Chem. Soc. 1987, 109, 1-4. 

Comproportionation has also been achieved with triphenyl-phosphonium methylide in benzonitrile (97) by Buck et al. (1972),... 

Another type of bidentate alkyl group is obtained by deprotonation of the phosphonium methylide (CH3)3P=CH2 and occurs in the dimeric alkyl [Cu(CH2)2P(CH3)2l2 (Figure 13). In this structure each copper atom has a cylindrical spd manifold with the linear sp hybrids forming two-center two-electron bonds with the alkyl carbons of two different (CH3)2P(CH2)2 groups. 

At least three names are available for the compound H3P=CH2. These are phosphine methylene, methylene phosphonium ylid and phosphonium methylide moreover, the compound can be classed as a phosphorane The compound PhjP Rj may be called triphenylphosphonium methylide, tri-phenylphosphonium methanide or triphenyl-methylenephosphorane. The pyridine analogue, C5H5P, has been known variously as phosphobenzene, phosphabenzene, phosphorin, and most recently, phosphinine. The term phosphane for (1) in Table 1.4 and its derivatives is the most recent and the most systematic, but it is difficult to see how the more widespread and firmly rooted term phosphine will ever be replaced. In addition, adoption of the term phosphane would put it in line with such little-used terms as carborane for CH4, nitrane for NH3 and oxane for HjO. 

The commonest phosphonium ylids are the triphenyl phosphonium methylides (known also as triphenylphosphine methylenes, methylene triphenylphosphoranes or triphenylphosphonium meth-anides). These may be represented as a hybrid of the forms (6.406) and can be regarded as carban-ions whose ionic character is modified by the adjacent positive charge. In addition, dtt-pjt bonding is to be expected and the contribution of the right-hand structure will increase as the n character of the bond is increased. 

The phosphonium methylide of (ii)-BINAP was used as a novel chiral disymmctric chelating ligand in the stable [Rh(cod)(BINAPCH2)] complex 273. The complex was obtained by the reaction of [Rh(/tt-Cl)(cod)]2 and the methylbinapium ylide. ... 

Whereas phosphonium ylides normally react with carbonyl compounds to give alkenes, dimethylsulfonium methylide and dimethylsulfoxonium methylide yield epoxides. Instead of a four-center elimination, the adducts from the sulfur ylides undergo intramolecular displacement of the sulfur substituent by oxygen. In this reaction, the sulfur substituent serves both to promote anion formation and as the leaving group. 

Finally, diphenylsulfonium-bis-(methoxycarbonyl)methylide, IX [87], and salts of p,p -bis-[(triphenylphosphonio)methyl]-benzophenone, X [88], have been claimed as photoinitiators of free radical polymerizations [89]. They presumably photolyze homolytically in the case of X, intramolecular triplet energy transfer from the benzophenone chromophore to the phosphonium moieties may likely be involved. 

To introduce chirality at C(3), the key intermediate chosen was the protected hydroxyketone 27 (Scheme 7) [33] which was first reacted with dimethyl sulphonium methylide to give the crystalline allylic epoxide 28 (characterized by m.p. and [aj [33] and X-ray analysis [24]). This was readily transformed into f/ )-3-hydroxy-p-cyclocitral (29) via the intermediate aldehydes 30 and 31. Base-catalysed condensation of 29 with acetone gave f/ j-3-hydroxy-p-io-none (32) which was converted into the corresponding crystalline acetate 33 (characterized by m.p., [ajp and CD [34]). Vinylation of 33 furnished a mixture of epimeric vinyl carbinols 34 which were treated with triphenylphosphine and hydrochloric acid. The Ci5-phosphonium chloride 35 thus obtained was identified by m.p., [aj HPLC, IR and H-NMR [33-35]. Contrary to expectations, no racemization at C(3) or dehydration to 3,4-didehydro compounds occurred under the conditions described. 

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