Regioselective Transformation of O-Propargylic Arylaldoximes to Four-Membered Cyclic Nitrones by Copper-Catalyzed Skeletal Rearrangement

Abstract

(E)-O-Propargylic arylaldoximes were regioselectively converted, in the presence of copper catalysts, into their corresponding four-membered cyclic nitrones in good to excellent yields. The reactions proceeded via a tandem [2,3]-rearrangement and 4π-electrocyclization of the N-allenylnitrone intermediate and involved cleavage of the carbon-oxygen bond.

Copper‐Catalyzed Skeletal Rearrangement of O‐Propargyl Oximes: A Mechanistic Manifold

“… Different compounds reported by Nakamura et al . from the Cu‐catalyzed rearrangement of O ‐propargyl oximes.…”

“…They changed only certain reactionp arameters and modified the substituents of this organic skeleton and obtainedavariety of N-containing cyclic and acyclic compounds and thus furnished this chemistry with strong versatility. [10][11][12][13][14][15] Notably,t hey found ad ependence between the electronic nature of the aryl group at the oxime moiety (R 3 in Figure1)a nd the product obtained in the Cu-mediated rearrangemento fO-propargyl arylaldoximes. If R 3 is an electron-poor aromatic group, four-membered cyclic nitrones 4 (azete oxides) are produced.…”

“…reported on the skeletal rearrangement of different O ‐propargyl aldoximes catalyzed by Cu. They changed only certain reaction parameters and modified the substituents of this organic skeleton and obtained a variety of N‐containing cyclic and acyclic compounds and thus furnished this chemistry with strong versatility . Notably, they found a dependence between the electronic nature of the aryl group at the oxime moiety (R 3 in Figure ) and the product obtained in the Cu‐mediated rearrangement of O ‐propargyl arylaldoximes.…”

“…Although Nakamura et al . performed a thorough synthetic study to transform a series of O ‐propargyl oximes into several different substrates in an efficient one‐pot fashion, the mechanism that these rearrangement reactions follow is still not clear.…”

Copper-Catalyzed Skeletal Rearrangements ofO-Propargylic Oximes via Cleavage of a Carbon-Oxygen Bond

“…[] Furthermore, the process produced a variety of multisubstituted heterocycles or nitrogenous acyclic compounds that are potentially useful in the fields of pharmaceutical or agrochemical sciences. In this account, we present our recent developments in the copper‐catalyzed intramolecular transformations of O ‐propargylic oximes via cleavage of the carbon–oxygen bond, leading to four‐membered cyclic nitrones (azete oxides),[] pyridine N ‐oxides,[] and amidodienes (Scheme ). [] However, before we present the experimental results of these reactions, we would first like to share the events leading up to our fortuitous encounter with the beautiful molecule.…”