Ylides triphenylphosphonium methylides

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). 

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). 

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... 

---