Azetidinone epoxides

Cleavage of an azetidinone epoxide.1 MgBr2, prepared from Mg with BrCH2CH2Br, cleaves the epoxide 1 regiospecifically to the diastereomeric bromo-hvdrins 2. The N-silyl derivative of 1 is stable under the same conditions. The ketone corresponding to 2 is a useful precursor to a carbapenem. 

Di Fabio et al. reported synthesis of 3-alkoxy-substituted trinems from commercially available 4-acetoxy-3-[(R)-l-f-butyldimethylsilyloxyethyl]-2-azetidinone. Epoxide 20 was treated with ceric ammonium nitrate in acetonitrile to provide the intermediate nitrate ester 21 in 55% yield. Simultaneous protection of the secondary alcohol and the amide was accomplished using di-f-butylsilyl bis(trifluoromethanesulfonate) to provide the tricyclic /3-lactam 22. Removal of the nitro group by catalytic hydrogenation provided the desired secondary alcohol that was alkylated with allyl bromide to provide 23 in quantitative yield (eq 10). ... 

The susceptibility of the amide bond of azetidinones to nucleophiles has been utilized for the synthesis of many heterocycles. Pyrrolidinones (103) may be obtained by treatment of the epoxide (102) with amines, whereas a paper by Crockett et al. draws attention to the long known but little used preparation of imides [e.g. (104)] by heating di-acids or anhydrides with urea. It is claimed that the reaction is easily managed on a large scale and that yields are often better than those of other procedures. 

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