Azetidin-2-one nucleus

The stereoselective synthesis of classical trinems (fused tricyclic systems having the azetidin-2-one nucleus fused through the N-C4 bond) <98MI347> and the chemistry of non-classical polycyclic P-lactams have been reviewed <00T5743>. 

The Staudinger reaction, i.e. the [2+2] ketene-imine cycloaddition, is the most frequently employed procedure of synthesis of the azetidin-2-one nucleus. Base-promoted cyclization of suitable linear substrates is another frequently employed procedure. We wish to report the electrochemical methodologies of synthesis of P-lactams, according to both procedures, and the possible utilization of RTILs (as solvents and/or as parent of intermediates). 

Scheme 16.3 Synthesis of the azetidin-2-one nucleus via the Staudinger reaction the [2+2] ketene-imine cycloaddition...

The synthesis of the azetidin-2-one nucleus, via the classical annulation of acetyl-chlorides with imines, requires more than stoichiometric amounts of Uiethylamine (about 3 equivalent), which cannot be recovered and reused. In addition, the procedure needs a large amount of organic solvents (VOCs) and, as a consequence, causes a large amount of waste. To overcome these difficulties, the possible ytterbium (III) triflate-catalysed stereoselective synthesis of P-lactams via [2+2] cyclocondensation in ionic liquids has been investigated by Su et al. (Scheme 16.4) [93]. 

Joshi et al. [81] have incorporated azetidin-2-one moiety into indole nucleus and synthesized several fluorine containing spiro-(3-lactams (Scheme 9). The synthesis involved the condensation of primary amines with an appropriate indole-2,3-dione... 

Tetrabutylammonium cyanide catalyses ring expansion of 4-(arylimino)methyl-azetidin-2-ones to 5-aryliminopyrrolidin-2-ones through a novel N(l)-C(4) bond cleavage of the /3-lactam nucleus and provides for an efficient one-pot protocol to enantiopure succinimide derivatives (Scheme 20).36... 

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