Studies on the [2,3]-Stevens rearrangement of aziridinium ions

The aziridinium ylide generated by the intramolecular reaction of a metal carbenoid tethered to a vinylaziridine undergoes 2,3]-Stevens rearrangement to furnish the indolizidine skeleton. It is essential that the correct nitrogen invertomer is used or a competing 1,5]-hydrogen shift predominates. During the preparation of a second system a `one-pot' acylation-3,3]-Claisen rearrangement was observed, delivering a seven-membered lactam.