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Azomethine ylide [3 + 2]-cycloaddition reactions are among the most powerful and well-studied chemical transformations to construct five-membered nitrogen-containing frameworks. However, cycloadditions of azomethine ylides bearing N-alkoxy substituents have largely been overlooked. This has been the case despite the potential for (1) accessing heterocycles with good regio- and diastereocontrol, (2) the presence of a cleavable tether which can be manipulated downstream via N–O bond cleavage, and (3) the promise of interesting structural diversity. Herein, we describe our efforts toward dirhodium-catalyzed intramolecular N-alkoxyazomethine ylide generation from α-diazoketo and -β-ketoester oximes and the disparate reactivities observed. Image 1 • New classes of O -tethered α-diazoketo and α-diazo-β-ketoester oximes were synthesized. • Treatment of α-diazo-β-ketoester oxime with dirhodium catalyst formed N -alkoxyazomethine ylide. • Transient ylide underwent [3+2]−cycloaddition reactions in presence of dipolarophiles. • Competing ylide N-O bond cleavage and cyclization formed oxazines and oxazoles. • Computational analysis offered support to the observed disparate ylide reactivities. [ABSTRACT FROM AUTHOR]