4-Propargyl-2-azetidinones

A convenient approach to synthesize novel selenium-(3-lactams, namely 3-selena-l-dethiacephems 200, was accomplished via the regioselective iodocycli-zation reaction (Scheme 73) [103]. The key starting materials, alkyne-selenoureas 201, for this approach were readily prepared by the A-alkylation reaction of the corresponding previously known propargyl-azetidinones with a wide variety of isoselenocyanates under basic conditions. First, the reaction of (3-alkyne-selenourea... 

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). ... 

A propargylic group was introduced onto the C-3 of the 4-acetoxy-2-azetidinone 184 by a zinc-mediated Barbier-type reaction of the latter with propargyl... 

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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