Phosphorus-containing groups ylides

Other examples of functionalization at C-2 via phosphorus ylides and phosphonate carbanions are described in Section 4.12.11. Utilization of 2-non-phosphorus-containing carbanions was also exemplified. Thus, 2-silicon-substituted 1,3-benzodithioles were synthesized via deprotonation of benzo-l,3-dithiole 245 with -BuLi and subsequent treatment of the resulting anion with trimethylsilyl chloride (TMSCl) to give 2-(trimethylsilyl)-benzo-l,3-dithiole 246 (Scheme 29). The second silyl group was introduced by further deprotonation of 246 ( -BuLi) followed by the reaction with an additional equivalent of TMSCl. Tin-substituted benzo-l,3-dithioles were synthesized in a similar way but the deprotonation of the monostannyl derivative was carried out with LDA (Scheme 29) <1996CL171>. 

Phosphorus ylide reacts rapidly with aldehydes and ketones to produce an intermediate called a betaine. Betaines are unusual since they contain negatively charged oxygen and positively charged phosphorus. Phosphorus and oxygen always form strong bonds, and these groups therefore combine... 

Trimethyl phosphine gave a still unidentified yellow, crystalline Mo-containing product which lacks aryl groups preliminary evidence is consistent with liberation of the diarylmethylene moiety to form a free phosphorus ylide. 

Compound 1295 undergoes a smooth reaction in boiling THE to produce triphenylphosphine oxide and l-(tri-fluoromethyl)-3/f-pyrrolizines 1296 that may be considered as a product of an intramolecular Wittig reaction (Scheme 247) <2006ARK55>. The tautomeric l//-pyrrolizine 1297 was not formed. When phosphorus ylides containing the trichloromethyl group 1298 were heated in THE the expected pyrrolizine 1299 was not formed, and the 2,2,2-trichloro-l-(l//-pyrrol-2-yl)ethanone 1300, dialkyl 2-butynedioate and triphenylphosphine were obtained instead (Scheme 248). 

Since that time, very many phosphorus ylides have been treated with compounds containing carbonyl groups. 

It has been found that nonstabilized ylides derived from the tetrahydro-phosphole nucleus (90 or 91) afford oxaphosphetanes that decompose at room temperature. Sin( 89, the phosphonium salt precursor of 90, contains only one alkyl group, BTP ylide 90 can be recommended for E-selective alkene synthesis in cases where the alkyl substituent must be used efficiently. Since the phosphorus environment in 90 is relatively expensive, this family of reagents will not provide a practical solution for large-scale synthesis of... 

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