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A three-component, general and practical route for diastereoselective synthesis of aza-spirocyclic pyrazolones via a decarboxylative annulation process

An efficient, general, and practical route for highly diastereoselective synthesis of aza-spirocyclic pyrazolones from easily available α-amino acids, aldehydes, and alkylidene pyrazolones by means of a decarboxylative annulation process is reported. This high-yielding reaction proceeds through a [3+2]-cycloaddition reaction between alkylidene pyrazolones and a nonstabilized azomethine ylide generated in situ. This method provides easy and smooth access to a variety of highly functionalized aza-spirocyclic pyrazolones in excellent yields (up to 96%). The obtained spiro-pyrazolones comprise four contiguous stereogenic centers including a quaternary carbon center.