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Z. Naturforsch. 2014,
69b, 615 – 626
doi:10.5560/ZNB.2014-4011
Cu(I)-catalyzed [3+2] Cycloadditions of tert-Butyl (S)-(3-Oxopent-4-yn-2-yl)carbamate to 1-Benzylidenepyrazole-3-one-derived Azomethine Imines
1 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia
2 EN-FIST, Centre of Excellence, Trg Osvobodilne fronte 13, 1000 Ljubljana, Slovenia
Reprint requests to Prof. Dr. Jurij Svete. Fax: +386 1 2419 220. E-mail:
jurij.svete@fkkt.uni-lj.si
Received January 24, 2014 / published online May 7, 2014
Parallel screening of suitable reaction conditions for Cu(I)-catalyzed [3+2] cycloadditions of (1Z,4R*,5R*)-4-benzoylamino-1-benzylidene-5-phenyl-3-oxopyrazolidin-1-ium-2-ide (1a) to methyl propiolate (2) has established that this reaction proceeds smoothly at room temperature in acetonitrile in the presence of CuI and Hünig's base. The optimized reaction conditions were then applied in regio- and stereo-selective 1,3-dipolar cycloadditions of racemic azomethine imines 1a–e to tert-butyl (S)-(3-oxopent-4-yn-2-yl)carbamate (6) leading to mixtures of diastereomeric non-racemic chromatographically separable cycloadducts 7a–d, 7′a–d, 8e, and 8′e. The structures of the products were confirmed by NMR spectroscopy.
Key words: 1,3-Dipolar Cycloaddition, 3-Pyrazolidinones, Catalysis, Copper, Acetylenes