NMR studies on [2+3] cycloaddition of nitrile oxides to cyclohexene derivatives

•Site selectivity and regioselectivity of the [2+3] cycloaddition reaction was established by 2D NMR spectroscopy.•Outstanding effect of carbohydrate-ytterbium triflate catalysts on selectivity of the reaction was demonstrated.•Influence of alkene electron densities on cycloaddition to cyclohexene derivatives was found.•Complete 1H and 13C NMR characterization of 3a,4,5,6,7,7a-hexahydro-1,2-benzoxazoles was achieved.

Site selectivity, regioselectivity and stereoselectivity of [2+3] cycloaddition of 4-trifluoromethylbenzonitrile oxide to cyclohexene carboxylates substituted with alkenyl functions were examined. Site selectivity was correlated with electron charges of alkenyl carbon atoms. Structure of the products has been established by an extensive application of 2D 1H and 13C NMR spectroscopy and electrospray ionization mass spectrometry.

Graphical abstract[2+3] Cycloaddition of nitrile oxides to conjugated ester substituted with 2-propenyl group occurs with a complete site selectivity and regioselectivity.Figure optionsDownload full-size imageDownload as PowerPoint slide