N-Alkylated unsaturated ketonitrones were efficiently synthesized from propargyloxyamines using Cu catalysts. Mechanisticstudies suggest that the rearrangement reaction proceeds via Cu-catalyzed intramolecular hydroamination, followed by thermally induced electrocyclic ring opening.
Multi-step cascadereactions of O-propargylicoximes with isocyanates were carried out in the presence of copper catalysts to afford the corresponding 1,6-dihydropyrimidines in good yields. The multi-step reactions consisted of a 2,3-rearrangement, a [3+2] cycloaddition, decarboxylative ring opening involving a 1,4-hydrogen shift, and a 6π-electrocyclization.
Copper-catalyzed skeletal rearrangement of O-propargylic aryloximes (E)-1 were carried out to afford the corresponding four-membered cyclic nitrones 2 in good to excellent yields. The optimal reactions conditions of the highly regioselective reactions involved the use of [CuCl(cod)](2) in acetonitrile at 70 degrees C. In the case of (Z)-1, however, the reaction proceeded in the absence of the copper catalysts to afford the identical compound 2 in good yields. Furthermore, the reactions were also carried out using chiral substrates (R)-1 in the presence of Cu catalysts to afford (R)-2 with good levels of chirality transfer.
Regioselective Transformation of <i>O</i>-Propargylic Arylaldoximes to Four-Membered Cyclic Nitrones by Copper-Catalyzed Skeletal Rearrangement
(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 4 pi-electrocyclization of the N-allenylnitrone intermediate and involved cleavage of the carbon-oxygen bond.