2-Azetidiniminium salts

Ab initio calculations indicate that in the gas phase the reaction of ketene inline and formaldehyde is concerted but asynchronous whereas in dichloromethane it is a two-step zwitterionic reaction.38 The 2 + 2-cycloadditions of keteniminium triflates with imines yields 2-azetidiniminium salts with cis stereoselectivity.39 The intramolecular 2 + 2-cycloaddition of ketenimines with imines (24) provides a novel synthesis of azeto[2,l-Z>]quinazolines (25) (Scheme 9).40... 

AZETIDINIMINIUM SALTS FROM KETENIMINIUM SALTS AND IMINES... 

Azetidiniminium salts - ° are available from the reaction of imines with iminium salts derived from tertiary carboxamides. These smoothly react with phosgene "- to yield a-chloroiminium... 

While cycloadditions of imines with ketenes or their precursors often produce cis P-lactams, the corresponding reactions of keteniminium salts are trans stereoselective (equations 70 and 71). 0 222 It is not clear whether the trans stereoselectivity is kinetic or results from an equilibration of 2-azetidiniminium salts under the basic conditions used in both cycloaddition and hydrolysis steps. 

Azetidiniminium salts have also been converted - into azeddine-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),... 

For reviews on the synthesis of p-lactams, see a) Sheehan JC, Corey EJ (1957) Org Reac 9 Chapt 6 b) Mukerjee AK, Srivastava, RC Synthesis 1973 373 b) Isaacs NS (1976) Chem Soc Rev 76 181 c) Bose AK, Manhas MS (1976) Lect Heterocycl Chem 3 43 d) Mukerjee AK, Singh AK (1978) Tetrahedron 34 1731 e) Koppel GA (1983) In Hassner A (ed) Small ring heterocycles-azetidines, p-lactams, diazetidines and diaziridines, Wiley, New York, Chapt 2 f) From azetidiniminium salts, see Ghosez L, Bogdan S, Ceresiat M, Frydrych C, Brynaert J, Portuguez MM, Huber I (1987) Pure Appl Chem 59 393... 

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