Ketenimines as Aza-Dienophiles

Abstract

N-Aryl ketenimines have been established as highly reactive aza-dienophiles. Intermolecular cycloadditions are achieved upon heating in the presence of 2,5-bis(silyloxy)furans and proceed with high levels of peri-, regio-, chemo- and diastereo-selectivity. Spontaneous C–O cleavage yields oxygenated pyridone derivatives in a highly convergent and redox-neutral manner. Combined experimental and computational studies demonstrate N-aryl ketenimines to be significantly more reactive than imino dienophiles, as a consequence of less distorted transition states. Derivatization studies include the development of isocyanate and cyclic ketenimine equivalents as aza-dienophiles, while extension to a one-pot aza-Diels–Alder/oxa-Diels–Alder sequence provides a three-component approach to complex fused pyridone/pyran systems.