Synthesis of Azetidine Nitrones and Exomethylene Oxazolines through a Copper(I)-Catalyzed 2,3-Rearrangement and 4π-Electrocyclization Cascade Strategy

Abstract

A variety of azetidine nitrones are prepared in moderate to good yields through copper(I) combined with 2-aminopyridine to catalyze skeletal rearrangement of O-propargylic oximes. Mechanistic studies reveal that the reaction undergoes a copper(I)-catalyzed tandem [2,3]-rearrangement, 4π-electrocyclization, ring opening, and recyclization over four steps in one pot. Substituents at the terminus of alkyne and oxime moieties have a significant impact on the formation of azetidine nitrones and exomethylene oxazolines, respectively. Furthermore, the obtained azetidine nitrone could easily participate in [3 + 2] cycloaddition with alkynoates, and a [2.2]-paracyclophane-derived azetidine nitrone is synthesized in 45% yield over five steps from bromo[2.2]-paracyclophane.

Iron(iii)/quinoxaline-derived N,N-ligand catalyzed oxygen transfer reaction of N-vinyl nitrones through selective 4π-electrocyclization and N–O bond cleavage

“…11 Recently, we also reported a copper( i )/2-aminopyridine catalyzed 2,3-rearrangement of O -propargylic oximes to afford N -allenyl nitrone intermediates, which then underwent two types of 4π-azaelectrocyclization. 12 The aforementioned examples have shown various azaelectrocyclizations of N -vinyl nitrones. However, 4π-azaelectrocyclization of N -vinyl-α,β-unsaturated nitrones has not yet been reported.…”