Azetidine hydrazones

The reactions of AyV-dialkylhydrazoncs with benzoyloxyketene <2002AGE831> and aminoketene <2004OL2749> precursors appear to be a new general approach to the enantioselective synthesis of 4-substituted 3-alkoxyazetidin-2-ones and 3-aminoazetidin-2-ones. Such hydrazones 488, derived from formaldehyde, afforded 4-unsubstituted azetidin-2-ones 489 (Equation 198) in 80-96% yields and dr s up to 99 1 <2004CEJ6111>. 

Enamines possessing /7-hydrogen atoms add hexafluoroacetone azine to form transient dipolar azomethine imines 9, as evidenced by low-temperature 19F NMR spectroscopy, which rearrange to hydrazones. If there is no hydrogen atom in the /7-position the betaines cyclize to unstable derivatives 10 of azetidine (equation 7)24. 

Azetidin 3-Chlor-2-oxo-l (4,5,6,7-tetrahydro-l,3-benzothiazol-2-ylamino)- El6b, 520 (Hydrazon + Cl-CH2-CO-Cl)... 

Azetidin 4,4-Bis-[trifluormethyl]-3,3-dimethyl-2-dimethylamino-l-(2,2,2-trifluor-l -trifluormethyl-ethyliden-amino)- EI6c, 798 (En-amin/Hydrazon)... 

Azetidiniminiutn salts have also been converted into azetidine-thiones, -imines or -hydrazones (Scheme 36). Yields of imine derivatives are high when the azetidiniminium salts bear no hydrogen atom at C-3. Otherwise the reaction is best effected by first forming the corresponding 2-azetidinethione which is further treated with an amine in the presence of mercury(II) acetate (Scheme 37). 

The asymmetric synthesis of 2-mono- and 2,3-/rtjw5-disubstituted azetidines 3 has been described <04EJO4471>. Key steps are a diastereoselective a-alkylation of aldehyde SAMP-hydrazones with benzyloxymethyl chloride as the electrophile, and a nucleophilic 1,2-... 

Malhotra et al. [33] described microwave-induced cyclocondensation of 3,5-diaryl-2-pyrazoline-l-carbaldehyde hydrazones (6) with chloroacetyl chloride to synthesize N-amino-3-chloro-4-(3,5-diaryl-2-pyrazoline-2-yl)-azetidine-2-one (7) (Scheme 4) however, the stereochemical aspect of the p-lactams was not considered. The antimicrobial evaluation of the resultant six p-lactams was performed against Escherichia coli, Proteus mlgaris, Klebsiella pneumoniae, and S. aureus. A few of these p-lactams showed moderate activity. 

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