Phosphorylated oxazolones

The displacement of the chlorine atom in 395 by triphenylphosphine or other phosphorus derivatives leads to the corresponding phosphorylated oxazolones 397 or 398 that have been used to prepare new and interesting substituted vinylphos-phonium salts (Scheme 7.127). Of particular interest is the synthesis of N-acyl-a-(triphenylphosphonio)glycinates as new cationic glycine equivalents. ... 

The activated phosphorus reagents 269 and 270 are conventionally prepared by the reaction of 2(3//)-oxazolone with the corresponding phosphorus chlorides in the presence of triethylamine. The phosphorus chlorides employed include phosphoryl chloride, thiophosphoryl chloride, mono- and dichlorophosphates, and phosphinic chloride (Fig. 5.66). 

The above reagents serve as condensing reagents and have different reactivities for peptides 279, p-lactams 281, esters, thioesters, and mixed phosphates, as well as for the direct preparation of 3-acyl-2(3F/)-oxazolones. The bis(2-oxo-3-oxazohnyl)phosphinate 282 is useful for Zr(IV)-catalyzed phosphorylation of alcohols, leading to the general synthesis of acid- and base-labile mixed phosphate esters 284 (Fig. 5.67). ... 

Whereas neutral oxazolones and the corresponding thiones are not particularly reactive with electrophiles, 2(3f/)-oxazolones (and benzoxazo-lones) give the 2-chloro derivatives on heating with phosphoryl chloride [77AHC(21)175]. With phosphorus pentachloride, though, 5-chlorination can occur (87JOU813) (Scheme 29). 

Neutral oxazolones and oxazolethiones are inert towards most electrophiles. 5(4//)-Oxazolones are reversibly protonated at the nitrogen atom. When the 2-oxazolone (194) is treated with sulfuric acid, 2-methyl-4,5-diphenyloxazole is produced (equation 31). 2(3/Z)-Oxazolones and benzoxazolones react with phosphoryl chloride to yield the corresponding 2-chloro-oxazoles and -benzoxazoles (equation 32). 

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