Absolute Configuration Determination of 2,3-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles Using Chiroptical Methods at Different Wavelengths

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• 作者：Eva Pušavec Kirar ; Uroš Grošelj ; Amalija Golobič ; Franc Požgan ; Stefan Pusch ; Carina Weber ; Lars Andernach ; Bogdan Štefane ; Till Opatz ; Jurij Svete
• 刊名：Journal of Organic Chemistry
• 出版年：2016
• 出版时间：December 2, 2016
• 年：2016
• 卷：81
• 期：23
• 页码：11802-11812
• 全文大小：593K
• ISSN：1520-6904

文摘

A correlation between the absolute configuration and chiroptical properties of nonracemic 1,6,7-trisubstituted 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles was studied. A series of 16 novel representatives were prepared by Cu-catalyzed [3 + 2] cycloadditions of racemic (Z)-2-benzylidene-5-oxopyrazolidin-2-ium-1-ides to tert-butyl (S)-(3-oxopent-4-yn-2-yl)carbamate, and their structures were determined by NMR, VCD, ECD, and X-ray diffraction. A clear correlation between the sign of specific rotation and configuration at position C(1) allows for easy determination of the absolute configuration of 1,6,7-trisubstituted 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by ECD and NMR. While VCD, requiring milligram quantities, allowed the determination of the correct relative and absolute configuration without additional information from other methods, the stereochemical analysis by ECD required knowledge of the relative configuration derived from NMR at a comparable computational level.