We successfully isolated a spiro imidazolidine-oxazolidine intermediate in the reaction of guanidinium ylide mediated aziridination using alpha-bromocinnamaldehyde. X-ray crystallographic analysis unambiguously revealed that the stereogenic centers of the spiro intermediate were in a trans configuration. The role of the spiro compound as an intermediate in the aziridination reaction was confirmed by observation of its smooth chemical conversion into aziridine products.
