Lidija Pezdirc

Copper(I) Iodide-Catalyzed Cycloadditions of (1Z,4R*,5R*)-4-Benzamido-5-phenylpyrazolidin-3-on-1-azomethine Imines to Ethyl Propiolate

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.

1,3-Dipolar Cycloadditions of (1Z,4R*,5R*)-4-Benzamido-3-oxo- 5-phenylpyrazolidin-1-ium-2-ides to Ethyl Propiolate

Abstract 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.