Monocyclic 2-azetidinones p-lactams

P-Lactams have been used as a synthon for the preparation of a vast array of compounds. It has been reported that the reduction of 4-(haloalkyl)azetidin-2-ones with LiAlhL is a powerful method for the synthesis of stereodefined aziridines and azetidines 06OL1101 . However, reduction of 4-(haloalkyl)azetidin-2-ones with chloroalane afforded 2-(haloalkyl)azetidines, which were rearranged to 3,4-cw-disubstituted pyrrolidines and piperidines 32 060L1105 . During these rearrangements, bicyclic azetidinium intermediates were formed which were ring opened by halides. The synthesis of a peptide- 

Key i) A1H2C1, Et20, RT. ii) MeCN, reflux, iii) MeONa, MeOH, RT. 

Key i) (a) /r-YCeTRNC, dioxane, reflux (b) HC1 (aq.), dioxane, reflux (c) TsOH, C1CH2CHC12, reflux. 

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Monocyclic azetidinones are useful building blocks in organic synthesis. Besides the wide use in the syntheses of monobactam antibiotics and nuclear analogues of natural bicyclic p-lactam antibiotics,1 2 3 new applications have appeared with the syntheses of unnatural a-amino acids, amino sugars4 and inhibitors of elastase.5 ... 

Acylamino-2-oxoazetidine-l-sulfonates, or monobactams (96), are monocyclic p-lactam antibiotics which are active against Gram-negative bacteria.7 Monobactams (96) may be prepared by either sulfonation of an azetidinone (97) with a sulfur trioxide complex or by cydisation of an acylsulfamate (98) (Figure 6). 

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