作者:Gabriela Huelgas、Sylvain Bernès、Mario Sánchez、Leticia Quintero、Eusebio Juaristi、Cecilia Anaya de Parrodi、Patrick J. Walsh
DOI:10.1016/j.tet.2007.10.010
日期:2007.12
The synthesis of atropisomeric 2-substituted benzamides 2a-e, 3a-e, and 4a-e, and characterization by X-ray structure analysis of 2d, 2e, 3c, 3e, 4c, and 4e are reported. Dynamic H-1 NMR spectroscopic studies of benzamides 2b-d, 3b-d, and 4b-d indicate that only two of the four possible rotamers are present in solution, with population ratios ranging between 1.5:1 and 4. 1:1. The measured free energy of activation to interconversion of the rotamers ranged from 12.4 to 18.9 kcal mol(-1). Benzamides ArCON[(S)-phenethyl]2 (2e, 3e, and 4e), exhibited atropisomer ratios between 1.7:1 and 1: 1, and free energies of interconversion of the rotamers ranged from 11.5 to 17.6 kcal mol(-1). The highest rotation barriers were observed for the ortho-nitro derivatives 2a-e. Molecular calculations at the semiempirical level (PM3MM) gave free energies of activation for benzamides 2e and 3e of 23.6 and 12.4 kcal mol(-1), respectively, which are comparable to the experimental values. (c) 2007 Elsevier Ltd. All rights reserved.