Isoxazoline-5-thiones

5-Haloisoxazolium salts were treated with Na2S to produce the above titled compounds (76ZC270). For example, 5-chloro-2-methyl-3-phenylisoxazolium tetrafluoroborate and Na2S gave 2-methyl-3-phenyl-3-isoxazoline-5-thione. 

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Sometimes, hydrogen sulfide converts an oxygen-containing heterocycle into a sulfur-containing one, and as furans and polycyclic furans are very common in nature such reactions may be the origin of the polycyclic thiophenes mentioned above. A typical example is the formation of the isothiazolin-3-thione (6) from the isoxazolin-3-thione (7) on treatment with hydrogen sulfide and hydrogen bromide.8... 

The tetrahydro-derivatives of the oxazole and isoxazole system are unstable. As a consequence, only acyclic products have been reported from the reductions with complex metal hydrides. 2,5-Diphenyl-oxazole (119) gave 2-benzylamino-l-phenylethanol (120),141 and 3,5-diphenyl-2-isoxazoline (121) was converted to 3-amino-l,3-diphenylpropanol (122)142 on reduction with lithium aluminum hydride. 3-Phenylbenzisoxazole was resistant to reduction with lithium aluminum hydride and sodium borohydride,143 but benz-oxazole (123), benzoxazol-2-one (124), and benzoxazol-2-thione (125) have been reported 141 to yield 2-methylaminophenol (126) on reduction with lithium aluminum hydride. 

More complex tautomeric equilibria have been observed for compound 21 involving the l,2,4,5-tetrazin-3-thione G. The equilibrium is strongly shifted toward the isoxazoline form A in solvents such as pyridine, acetone, dimethyl-sulfoxide (DMSO), and dimethylformamide (DMF), whereas the pyrazoline form D does not exceed 5-10% (Scheme 3) <2002CHE730>. The presence of the above tautomeric species has been demonstrated by NMR. 5-Hydroxy-3,3,5-trimethylisoxazolidine showed a similar behavior <2003CHE1257>. The presence of a CF3 group such as in 22 affects considerably the stmcture of these compounds, which exist only in the cyclic isoxazoline form <2000RCB1910>. 

The oxime of benzoylacetamide forms 5-phenylisoxazole (152) <58AC(R)577) on treatment with phosphorus pentasulfide, and on further treatment this is converted into 5-phenyl-l,2-dithiole-3-thione (90b). Also, isoxazoline-3-thiones (153) react with hydrogen sulfide to form mixtures of dithiol-3-imines (3c) and isothiazoline-3-thiones (40) (80CPB487). 

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