X=Y–ZH systems as potential 1,3-dipoles. Part 56: Cascade 1,3-azaprotio cyclotransfer–cycloaddition reactions between aldoximes and divinyl ketone: the effect of oxime E/Z isomerism on cycloaddition stereoselectivity

The cascade 1,3-azaprotiocyclotransfer (1,3-APT)-1,3-dipolar-cycloaddition (1,3-DC) reaction between aldoximes and divinyl ketone affords mixtures of exo and endo-isomers of substituted 1-aza-7-oxabicyclo[3.2.1]octan-4-ones, the ratio of which is dependent on the E/Z geometry of the starting oxime and its ability to isomerise under the thermal reaction conditions.