Nitrile Oxides, Imines, and Sulfides

The isoxazole nucleus that could be synthesized from nitrones can also be obtained from 1,3-dipolar cycloaddition of nitrile oxides. Quilico et generated benzonitrile oxides 53 from the benzhydroxamic acid chloride 52 precursor. The reaction involving MA with 52 gave, on work-up, a 77% yield of the adduct 54. 

Nitrile imines 55 add to dimethyl fumarate to yield 99% of the pyrazoline derivative 56.  

Nitrile sulfides 58 also can be generated in situ. Gunwell and Dye obtained a 20% yield of 3-phenyl-2-isothiazoline-c/5-4,5-dicarboxylic anhydride 59 by the treatment of 57 with MA in the presence of sodium fluoride  

Howe and Franz have recently obtained nitrile sulfide intermediates via thermolysis of 5-substituted l,3,4-oxathiazol-2-one 60. Thermolysis of the latter in the presence of an excess of dimethyl fumarate at 190°C gave 61 in a 45-55% yield. Similarly, iV-alkyl and A -arylmaleimides gave good yields of the heterocycles 62. 

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