Isocyanates 2-phenyl-4 -oxazolone

Aromatic a-ketols 48 react with (diethylamino)tributyltin to afford a mixture of (Z)- and ( )-l,2-enediol-types of bis-organostannylated compounds 49 that cyclize upon heating with phenyl isocyanate to give a 3,4,5-triaryl-2(3/f)-oxazolone 50 (Fig. 5.14). ... 

The 1,3-dipolar cycloaddition of a-keto carbenoids to the polar double bond of heterocumulenes provides a direct access to five-membered heterocycles. The reaction of a-diazo ketones 132 with phenyl isocyanate in the presence of a Rh2(OAc)4 catalyst affords the 1,3-cycloadduct, 3-phenyl-2(3//)-oxazolones 133 (Fig. 5.32). ... 

Monosubstituted-5(4//)-oxazolones behave differently upon reaction with imines. Here, 4-methyl-2-phenyl-5(4/7)-oxazolone 196 (Ri = Ph, R2 = Me) reacts with imines derived from 2-furancarboxaldehyde or 2-thiophenecarboxaldehyde to give 3-amino-p-lactams 197. On the other hand, 196 reacts with chlorosul-fonyl isocyanate in a [2 + 2] cycloaddition to give dioxazabicycloheptanones 198 as shown in Scheme 7.60. ... 

H)-Oxazolones are formed by the spontaneous cyclization of /3-oxo isocyanates (equation 134). Similarly, o-hydroxyphenyl isocyanate, produced by the Curtius rearrangement of the azide of salicylic acid or by the action of sodium hypochlorite on salicylamide, forms benzoxazolone (equation 135). An analogous reaction is the formation of IV-phenyl-benzoxazolone by the action of thionyl chloride on the hydroxamic acid shown in equation (136) (78TL2325). Pyrolysis of aryl azidoformates affords benzoxazolones by nitrene insertion (equation 137) (81CC241). 

H)-Oxazolones were unknown until 1949 when the 2-phenyl derivative was prepared by the action of diazomethane on benzoyl isocyanate (equation 145) (49JA4059). Treatment of the phospholene (293) with acyl isocyanates (294 R = Ph, MeO or Ph2N) affords 5-acetyl-5-methyl-4(5.flr)-oxazolones (equation 146). 

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