To test this hypothesis, aziridine 1 was treated with methylacetoacetate-derived 2e and catalytic Rh2(OAc)4 under optimized conditions (Scheme 4A, see Supporting Information for details). The dehydromorpholine 4e was obtained in 38% yield (48% by NMR), accompanied by the corresponding cheletropic extrusion product 5e (42% by NMR). Interestingly, no competing To experimentally interrogate the origin of 5e, NMR time-course data was collected to identify long-lived reaction intermediates or other products not observed in the final crude mixture.