Oxazepine Synthesis by Copper-Catalyzed Intermolecular Cascade Reactions between O-Propargylic Oximes and Dipolarophiles

摘要

π-Acidic metal-catalyzed rearrangement reactions have been often utilized in cascade reactions because the transformation efficiently generates reactive intermediates, which are generally hard to pre-prepare by conventional organic synthesis, under mild reaction conditions with high functional-group tolerance.' In particular, the cascade reaction involving an intermolecular process between a reactive intermediate and an external reagent is an attractive and elegant protocol for the construction of densely functionalized molecular skeletons in a single operation. Although the reactivities of the metal carbenoid intermediates, which are generated by alkyne π activation, typically drive the intermolecular process, cycloadditions have also been utilized as a viable alternative in an intermolecular fashion. Recently, we have developed π-acidic metal-catalyzed intramolecular reactions of O-propargylic oximes proceeding through a 2.3-rearrange-ment to form the corresponding N-allenylnitrone A (Scheme 1).