4-allenyl-2-azetidinone

Krause has shown that gold(III) salts catalyze the intramolecular emJo-hydroamina-tion of N-protected a-aminoallenes [35]. For example, treatment of the diasteromeri-cally pure a-allenyl sulfonamide 44 with a catalytic amount of AUCI3 in dichlor-omethane at 0 °C for 1 h formed the pyrroline derivative 45 in 95% yield with 96% diastereomeric purity (Scheme 11.6). The protocol tolerated aryl and alkyl substitution of the distal allenyl carbon atom and was also effective for the hydroamination of N-unprotected a-allenylamines although these latter transformations required considerably longer reaction time. In a similar manner, Lee has reported the gold (Ill)-catalyzed ewdo-hydroamination of 4-allenyl-2-azetidinone 46 to form bicydic P-lactams 47 (Eq. (11.25)) [36]. 

Propargyltrimethylsilanes give allenyl derivatives on reaction with -acyliminium precursors. - On the other hand, application of allenyl-silanes or -stannanes provides access to propargyl-substituted lactams. All reactions proceed with high regio- and stereo-selectivity (equations 54 and 55). 4-Allenyl-azetidinones can be cyclized to A -carbapenem systems, mediated by Ag or Pd salts. - The reactions of ethoxylactams with allenylsilanes can be modified in such a way that bicyclic systems are obtained in one step (equation 56). ... 

Methylethylidene)azetidinones. CSI reacts with the allenyl acetate 2 to give, after reduction, the unsaturated azetidinone 3, which was converted into the stable sulfide 4 in 44% overall yield. This product was converted in several steps into a carbapenem (5). Compounds of this type are potent p-lactamase inhibitors. 

Buynak and coworkers [23] introduced an interesting entry to synthesize 4-acetoxy-3-alkylidene-P-lactams (Scheme 5). The strategy involved addition of CSI to the allenyl acetate 31 followed by careful reductive workup to give the 4-acetoxy-3-(l-methylethylidene)-2-azetidinone 32 in 30% yield. Further... 

Gold-catalysed carbocyclization of (aryloxy)allenyl-2-azetidinones has been reported to proceed in an unusual 9-endo fashion, affording fused tricyclic -lactams. ... 

The iron(III) chloride-catalyzed ring expansion reaction of 2-azetidinone-tethered alkynols and allenols provides pyrroles or y-lactones, respectively (Scheme 4-351). The proposed mechanism for the pyrrole formation includes a Meyer-Schuster rearrangement of the propargyl alcohol to the corresponding allenyl alcohol, P-lactam ring opening, tautomerization of the allenyl alcohol to the a,P-unsaturated carbonyl compound, and cyclization by attack of the amino group to the ketone under dehydration. ... 

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