Polycyclic Pyrazolidines by Tandem Diazomalonate Dipolar Cycloadditions and CpRu-Catalyzed Carbene Additions
Claire Montagnon1, Joël R Bultel1, Céline Besnard2
1Department of Organic Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1211, Geneva 4, Switzerland.
Abstract:
Thanks to the ability of diazo derivatives to react either as 1,3-dipoles and as carbenes after dinitrogen extrusion, combinations of oxa or aza benzonorbornadienes and diazomalonates afford polycyclic pyrazolidines via a three-step sequence of (i) a highly diastereoselective [3+2]-cycloaddition, (ii) a CpRu-catalyzed carbene addition, and (iii) a second dipolar cycloaddition. Of importance, step (II) represents a unique access to novel bench-stable N,N-cyclic azomethine imines, which behave as effective 1,3-dipoles in combination with electron-poor dipolarophiles. Each step proceeds efficiently and the 3-step process can be performed in one-pot to yield a polycyclic pyrazolidine in excellent overall yield (90 %).
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