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Regioselective copper(i) iodide-catalyzed cycloadditions of chiral pyrazolidin-3-on-1-azomethine imines 3a–j to ethyl propiolate 4 gave cycloadducts 5a–h and 5′i and 5/5′j as single regioisomers. In terms of facial selectivity, cycloadducts 5a–h and 5′i were obtained as single diastereomers, whereas the reaction of dipole 3j was less selective and gave a mixture of 5j and 5′j in a ratio of 15:85. Stereoselectivity of copper(i) iodide-catalyzed cycloadditions of ethyl propiolate 4 to azomethine imines 3 was controlled by the stereodirecting phenyl group at position 5 and by the ortho-substituents at the 1′–Ar residue.

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Combinatorial solution-phase cycloadditions of (1Z,4R*,5R*)-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines 3 to beta-keto esters 4 afforded a library of 26 bicyclic pyrazolidinones 5 in 6-89% yields and in 14-100% de. All products were isolated in >90% purity according to 1H NMR, and 25 of them were analytically pure. The structures of cycloadducts were confirmed by NMR and X-ray diffraction. Most of the products were isolated as mixtures of the major (1S*,2S*,3R*,5R*,6R*)-epimers 5 and the minor (1R*,2S*,3R*,5R*,6R*)-epimers 6. Epimerization of cycloadducts 5/6 at the anomeric position 1 in solution was confirmed by 1H NMR.

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1,3-Dipolar cycloadditions of (1Z,4R*,5R*)-4-benzamido-3-oxo-5-phenylpyrazolidin-1-ium-2- ides 3a - e to ethyl propiolate (4) were studied. The reactions were carried out in anisole under reflux and in anisole under microwave irradiation at 150°C. All reactions were quite non-selective and furnished mixtures of isomeric cycloadducts, 5, 5′ , 6, and 6′ , with ethyl (1S*,6R*,7R*)-6-benzamido-1- (4-nitrophenyl)-5-oxo-7-phenyl-1,5,6,7-tetrahydropyrazolo[1,2-a]pyrazole-2-carboxylates 5a - e as the major isomers. Pure major isomers 5a - e were obtained in low to moderate yields upon thorough chromatographic workup (CC followed by MPLC). The structures of cycloadducts 5, 5′ , 6, and 6′ were determined by 1H NMR and NOESY spectroscopy.

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Pyrazole derivatives R 0180Unexpected Cleavage of the N-N Bond in the Reactions of 3-Pyrazolidinone-1-azomethine Imines with HCN. -Treatment of the title compounds with HCN is assumed to cause cycloaddition with formation of pyrazolo-triazole products. However, substrates (I) undergo an unexpected reaction to give products (III) resulting from β-eliminative N-N bond cleavage. In the case of the mesityl derivative (IV), the proposed intermediate is stable and can be isolated. -(PEZDIRC, L.; GROSELJ, U.; MEDEN, A.; STANOVNIK, B.; SVETE*, J.; Tetrahedron Lett. 48 (2007) 30, 5205-5208; Fac. Chem. Chem. Technol., Univ. Ljubljana,