Triphenylphosphonium methylid

Bravo et al. studied the reaction of various ylides with monooximes of biacetyl and benzil. Dimethylsulfonium methylide and triphenylarsonium methylide gave 2-isoxazolin-5-ol and isoxazoles, with the former being the major product. Triphenylphosphonium methylide and dimethyloxosulfonium methylide gave open-chain products (Scheme 135) (70TL3223, 72G395). The cycloaddition of benzonitrile oxide to enolic compounds produced 5-ethers which could be cleaved or dehydrated (Scheme 136) (70CJC467, 72NKK1452). 

Thus Ph3P=CH2 is triphenylphosphonium methylide (see pp. 274-304 of reference 2, or textbooks of organic chemistry for a fuller treatment of the Wittig reaction). 

Wittig olefination of 5(4//)-oxazolones with triphenylphosphonium methylides affords product mixmres that depend on the ylide and the starting oxazolone. ° The product mixtures can include, apart from the expected 5(4//)-oxazolylideneace-tates, 5-oxazoleacetates, and other byproducts. Nevertheless, Wittig reaction of ethyl (triphenylphosphoranylidene)acetate with a 4,4-disubstituted-5(4//)-oxazo-lone 285 affords the corresponding ethyl 5(4//)-oxazolylideneacetates 286 in satisfactory yields (Scheme 7.93 Table 7.24, Fig. 7.26). 

TABLE 7.24 5(4//)-OXAZOLYLIDENEACETATES FROM REACTION OF SATURATED 5(4//)-OXAZOLONES WITH TRIPHENYLPHOSPHONIUM METHYLIDES, 193... 

The 5(4ff)-oxazolones undergo a variety of reactions, including those with nucleophiles at positions 2 and 5. Triphenylphosphonium methylides react to give 5-alkylidene derivatives (77) in addition to oxazoles (78), when isomerization is possible, and ring-opened products (79) (Equation... 

Following addition of triphenylphosphonium methylide, Wittig condensation, electrocyclic ring opening and double bond equilibration, all Iran -T-substituted 2,4,6-heptatrienals can be accessed. ... 

Having assembled the bicyclic framework, attention was directed toward introduction of the diylophile. Deprotection of the masked aldehyde in 46 and 47 was most efficiently accomplished using 70% aqueous acetic acid at 50-60 °C for 5 days (85% and 95% yield, respectively). The dimethyl dicarbamate was subjected to saponification with potassium hydroxide in refluxing ethanol for 1.5 hours, whereafter the in situ oxidation with potassium ferricyanide at 0 °C gave rise to the dizaene 48 in yields ranging from 76-86%. We were gratified to observe that treatment of 48 with triphenylphosphonium methylide in THF at room temperature led to the desired diyl precursor 41 in 56-83% yield. 

The diene function is introduced by reaction of 790 with the lithium salt of 2-triethyl-silylpropanal N-tert-hutyliminQ, which after hydrolysis produces an intermediate a,jS-un-saturated aldehyde. Subsequent Wittig condensation with triphenylphosphonium methylide then affords the diene 791. The final conversion to 792 requires six additional steps [223]. 

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 thiones (493 X = S or O) react with triphenylphosphonium methylide giving mixtures of the ylides (494) and the thiolactones (495)." ... 

The reactivity of xanthates towards nucleophiles has not been very extensively studied in the past. A new type of stable ylide (254) has been obtained by the action of triphenylphosphonium methylide on simple xanthates, and the reaction of the xanthates (307) with dimethylsul-phonium methylide in basic media revealed a new route to 3,5-disubstituted... 

Finally, triphenylphosphonium methylide could be added to reagent 1 to give a thioimidate substituted triphenylphosphonium methylide (eq 25). ... 

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