The computed reaction profile depicted in Scheme 3C also shows that the NCI-stabilized ylide INT4 can undergo a cheletropic extrusion reaction to form the alkene 5c. We hypothesized running the reaction at higher temperatures would: (i) enable facile bond rotation and lead to a greater preference for 4c over the [3,9]-aziridine product 3c and (ii) allow access to the cheletropic extrusion product. To our delight, repeating this reaction at 83 ˚C in 1,2-dichloroethane (Scheme 3A, left) favored dehydromorpholine 4c formation in 50% yield by H-NMR (47% isolated), with the remaining mass balance (45% yield) accounted for by formation of 5c; no [3,9]-aziridine 3c formation was observed. Although full selectivity for 4c would be optimal, this reaction represents the first example where the fate of the aziridinium ylide can be controlled by the reaction conditions and not just the identity of the carbene precursor. Employing higher temperatures with other cyano-derived diazoketones also proved fruitful (Scheme 3C). Ketones bearing ortho-, meta-and para-chlorosubstituted benzenes yielded dehydromorpholines 6c-8c in moderate yields and excellent dr of >20:1. The cyano group of dehydromorpholines 6c-8c is readily reduced to a primary amine for attaching these Nheterocycles to a DNA headpiece for preparing DNA-encoded libraries, while the aryl chloride is an excellent functional handle for diversification of DELs. Ketones with meta-and paramethoxysubstituted benzenes were tolerated to furnish dehydromorpholines 10c and 11c in 43% and 29% yield, respectively. The ortho-substituted 9c was not obtained under these conditions, possibly due to steric congestion around the reactive site that prevents effective ylide formation.