Indolizidine-7-one

Alkyl azides have been involved in the synthesis of indolizidinone derivatives in several ways. One example (Scheme 7) is the intramolecular Schmidt reaction between alkyl azides and ketones which can be used to transform azidoketone 24 into the corresponding indolizidinones 26 through intermediate 25 <2001JOC886> or with epoxides to obtain the indolizidine 27 <2004JOC3093>. 

The Lewis acid-catalysed 3 + 2-cycloaddition of aziridine-2-carboxylates with isocyanates proceeds regio- and stereo-specifically to produce enantiomerically pure 4-substituted imidazolin-2-ones in high yields.33 The reaction of ethyl 7-iodo-2-heptynoate (27), 2-arylaziridines (28), and K2C03 produces polysubstituted indolizidines (30) via an S /formal 3 + 2-cycloaddition (29) process (Scheme 8).34... 

The dendrobatid toxin 25 ID (18) has been synthesized by a new approach which utilizes an iminium-vinylsilane cyclization to produce the (Z)-6-alkylidene-indolizidine ring-system in a stereospecific manner. The key intermediate (19) was prepared from L-proline and converted into toxin 25 ID (18) by reaction with paraformaldehyde and (+)-camphor-10-sulphonic acid in refluxing ethanol. The method is potentially a general one for forming unsaturated azacyclic rings, and it provides a convenient route to the pumiliotoxin A alkaloids.7... 

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