Condensation of 4-methylacetophenone (I) with ethyl diethoxyacetate (II) in the presence of lithium hexamethyldisilazide afforded diketoacetal (III). Formation of pyrazole (V) was accomplished by treatment of (III) with 4-methoxy-phenylhydrazine (IV). Subsequent acid hydrolysis of the diethyl acetal gave aldehyde (VI), which was condensed with carbon tetrabromide using triphenyl phosphine to furnish dibromoethylene compound (VII). Elimination of HBr in (VII) by treatment with tetrabutylammonium fluoride produced bromo-acetylene (VIII). After lithium-bromine exchange, addition of paraformaldehyde yielded the propargyl alcohol (IX). Further Mitsunobu coupling of (IX) with N,O-bis(phenoxycarbonyl)hydroxylamine (X) gave the N,O-bis-protected N-alkyl hydroxylamine (XI). This was finally converted to the title N-hydroxyurea by treatment with methanolic ammonia.

Condensation of 4-chloroacetophenone (I) with ethyl diethoxyacetate (II) in the presence of lithium hexamethyldisilazide afforded diketoacetal (III). Formation of pyrazole (V) was accomplished by treatment of (III) with 4-methoxy-phenylhydrazine (IV). Subsequent acid hydrolysis of the diethyl acetal gave aldehyde (VI), which was condensed with carbon tetrabromide using triphenyl phosphine to furnish dibromoethylene compound (VII). Elimination of HBr in (VII) by treatment with tetrabutylammonium fluoride produced bromoacetylene (VIII). After lithium-bromine exchange, addition of acetaldehyde yielded the propargyl alcohol (IX). Further Mitsunobu coupling of (IX) with N,O-bis(tert-butoxycarbonyl)hydroxylamine (X) gave the N,O-bis-protected N-alkyl hydroxylamine (XI). After Boc deprotection of (XI) by means of trifluoroacetic acid, coupling with acetyl chloride provided the O-acetyl hydroxamic acid (XII). Finally, cleavage of the O-acyl group of (XII) with methanolic NaOH furnished the title compound.

Condensation of 4-methylacetophenone (I) with ethyl diethoxyacetate (II) in the presence of lithium hexamethyldisilazide afforded diketoacetal (III). Formation of pyrazole (V) was accomplished by treatment of (III) with 4-methoxy-phenylhydrazine (IV). Subsequent acid hydrolysis of the diethyl acetal gave aldehyde (VI), which was condensed with carbon tetrabromide using triphenyl phosphine to furnish dibromoethylene compound (VII). Elimination of HBr in (VII) by treatment with tetrabutylammonium fluoride produced bromo-acetylene (VIII). After lithium-bromine exchange, addition of paraformaldehyde yielded the propargyl alcohol (IX). Further Mitsunobu coupling of (IX) with N,O-bis(phenoxycarbonyl)hydroxylamine (X) gave the N,O-bis-protected N-alkyl hydroxylamine (XI). This was finally converted to the title N-hydroxyurea by treatment with methanolic ammonia.

Condensation of 4-chloroacetophenone (I) with ethyl diethoxyacetate (II) in the presence of lithium hexamethyldisilazide afforded diketoacetal (III). Formation of pyrazole (V) was accomplished by treatment of (III) with 4-methoxy-phenylhydrazine (IV). Subsequent acid hydrolysis of the diethyl acetal gave aldehyde (VI), which was condensed with carbon tetrabromide using triphenyl phosphine to furnish dibromoethylene compound (VII). Elimination of HBr in (VII) by treatment with tetrabutylammonium fluoride produced bromoacetylene (VIII). After lithium-bromine exchange, addition of acetaldehyde yielded the propargyl alcohol (IX). Further Mitsunobu coupling of (IX) with N,O-bis(tert-butoxycarbonyl)hydroxylamine (X) gave the N,O-bis-protected N-alkyl hydroxylamine (XI). After Boc deprotection of (XI) by means of trifluoroacetic acid, coupling with acetyl chloride provided the O-acetyl hydroxamic acid (XII). Finally, cleavage of the O-acyl group of (XII) with methanolic NaOH furnished the title compound.