Initial explorations of diverse carbene precursors. We first investigated whether the carbonyl oxygen of a donor-acceptor diazoketone, such as 2a, could serve as a competent nucleophile to open the aziridinium ylide en route to a dehydromorpholine (Scheme 2A). Only one nucleophilic ketone group is present in 2a; thus, we expected reaction of 2a with 1 to furnish 4a in good yield via conformer INT1. Surprisingly, treatment of 1 with 2a under Rh2(OAc)4 catalysis gave an unusual [3,9]-aziridine product 3a in 78% yield. Presumably, the 7 kcal/mol barrier to interconversion of aziridinium ylide INT1 to INT2 via rotation around the C-N bond (Figure , vide infra) enables nucleophilic attack of the ketone oxygen on the carbonyl of the carbamate tether to furnish 3a. This result was unexpected, as nucleophilic addition to the carbamate tether was not observed in previous syntheses of azetidines or dehydropiperidines from bicyclic aziridines. We were curious as to the origin of 3a and surmised it might arise from a non-covalent interaction (NCI) in the aziridinium ylide intermediate INT2 that biases the reaction towards this unexpected product. Helliwell and co-workers reported evidence for NCIs between carbonyls and aromatic π-electron clouds; we wondered if a similar interaction between the ketone phenyl group and the carbamate carbonyl group might be operative in the transition state. However, exchanging the Ph group of 2a to a Me group in 2b still furnished 3b in an excellent 98% yield.