The first report of unusual flipping of the cycloadducts from 1,3-dipolar cycloaddition of 3,4,5,6-tetrahydropyridine N-oxide to N-cinnamoyl piperidines

A series of cycloadducts possessing unusual flipping modes have been isolated from the 1,3-dipolar cycloaddition of 3,4,5,6-tetrahydropyridine N-oxide to piperidides of cinnamic acid and para-substituted cinnamic acids and these were analyzed by X-ray crystallography to reveal novel solid-state structures. The presence of two different flippomers arising due to flipping of the six/five bicyclic ring was confirmed both in solid state and in solution. This is the first observation of 1,3-dipolar cycloadducts having two different flippomers arising due to flipping of the isoxazolidine ring.