The 1-(2-aminoethyl)aziridine (aziridine dimer) 1 reacts with acetylen
e dicarboxylates to give 1,4-diaza-5-oxobicyclo[4.3.0]nonanes (7-azain
dolizines) 3 together with the usual enamine adducts 4; the product st
ructures are confirmed spectroscopically and, in the 3 also by X-ray d
iffraction and by an independent synthesis from furan 5.