Carbonyl-stabilized ylides

A review concerning the coordination and organometallic chemistry of P- and As-carbonyl stabilized ylides was published in1998. The references quoted inside, being previous to the period concerned by our article, are not detailed here but they represent a very interesting basis to the results described below [66]. 

Carbonyl-stabilized ylides and the cyano-stabiHzed ylides Ar3P=CHCN in spite of their low nucleophilicity are able to give stable complexes. By comparison, very few complexes involving the second category of ylides are known. However a new example has recently been described by reaction of the cyano-ylide 60 with palladium(II) to give the complex tra s-[PdCl2 CH(PTol3)CN 2] 61 (Scheme 24) [93]. 

Alkylation of carbonyl-stabilized ylides gives alkoxyvinylphosphonium salts (121), which are reported118 to rearrange to the ketophosphonium salts (122). In contrast, the thioalkylvinylphosphonium salts (123) appear to be stable.119... 

Phosphonium ylides form complexes with almost every metal of the periodic table [8-13]. The first ylide complexes involved carbonyl-stabilized ylides at Pd (II) and Pt(II) metal centers. One early example was reported by Amup and Baird in 1969 [61]. The scope of the ylide coordination chemistry was then extensively investigated by Schmidbaur [8]. 

The stabilized ylides have at least one substituent on the ylidic carbon that can either conjugate with the P=C rcbond (16a) or delocalize the carbanion charge (16c). Most of the crystal structures of the stabilized ylides have a carbonyl group attached to the ylidic carbon, although other groups are represented. The dominant resonance structures of the carbonyl stabilized ylides are shown in 16a-c. A summary of the X-ray structural data for the stabilized ylides is given in Table 3. 

Cationic bis(yhde) complexes [Ag(ylide)2]+ can be isolated only with aryl substituted ylide ligands of the formula Ph3P=CHR. They have been synthesized by the reaction of silver salts AgX (X = Cl, CIO4, N03) and free ylides in a 1 2 molar ratio. A large variety of different simple ylides (R = H, Me, CH(CH3)2)11,13 and carbonyl stabilized ylides [R = C(0)Me, C(0)Ph, C02Me, C02Ph]14 have been employed in this reaction. 

Nearly all of the results available through 1967 could be interpreted to tell a consistent story. Betaines corresponding to carbonyl-stabilized ylides or to benzylic ( moderated ) ylides apparently were capable of extensive reversal, at least in hydroxylic solvents. Betaines corresponding to nonstabi-... 

Organic superbases effectively generate carbonyl-stabilized ylides to promote Wittig reactions. In the synthesis of (-)-mycalolide A (68) by Panek and Liu, construction of... 

The Stevens rearrangement of carbonyl stabilized ylide 73 with aqueous sodium hydroxide at room temperature afforded the quinoxalinone 75 through the migration of the benzyl moiety of the intermediate ylide 74. ... 

The new reagent (PhO)3PMe CF3S02 overcomes the problems associated with side-reactions in the Arbuzov reaction ROH displaces one PhO group and reacts with added nucleophiles to give products including ROR, RCN, RNCS, and RI. The phosphonium salt (84), derived by O-alkylation of a carbonyl-stabilized ylide, functions in a new synthesis of cyclohexenones, via (85), by condensation with a ketone. 

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