Stereodefined monocyclic, spirobicyclic, and bis-spirotricyclic pyrazolidin-3-ones can be prepared efficiently by a three-component reaction involving a 1,3-dipolar cycloaddition of azomethine imines obtained from hydrazones with α-oxo-ketene dipolarophiles generated in situ. The reaction allows the creation of four covalent bonds and two contiguous chiral quaternary centers with excellent diastereoselectivity in a single catalyst/additive-free, highly atom-economical transformation. From a fundamental point of view, the reaction introduces α-oxo-ketenes as effective dipolarophiles in 1,3-dipolar cycloadditions.
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Presset et al. (2011) studied this question.
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