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Cyclization of thiocyanomethylketone oximes with hydroxylamine hydrochloride and oxidation of 2‐aminothiazole derivatives with peracids are shown to afford the same products, which can be formulated either as 2‐imino‐3‐hydroxy‐2,3‐dihydrothiazolines or 2‐aminothiazole N‐oxides. Compounds of this type bearing at position 4 an acetic or α‐oxyiminoacetic residue are useful synthons for highly active β‐lactam antibiotics; the problems connected with their preparation in a suitably protected form are examined. Scope and limitations of this previously unreported oxidation of the thiazole nucleus are discussed. All the products show limited stability in alkaline media: the 4‐acetic derivatives, in addition, undergo a transposition to afford 4‐methylidenethiazolidines. Possible types of isomerism and tautomerism are discussed in the light of the acquired spectral data. The uv and ir spectra of the compounds synthesized lend support to their formulation as 2‐aminothiazole N‐oxides.

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