Synthesis of Bulky Aryl Group-substituted Chiral Bis(guanidino)iminophosphoranes as Uncharged Chiral Organosuperbase Catalysts
Tadahiro Takeda A and Masahiro Terada B C
+ Author Affiliations
- Author Affiliations
A Process Technology Research Laboratories, Daiichi Sankyo Co., Ltd, Edogawa-ku, Tokyo 134-8630, Japan.
B Department of Chemistry and Research and Analytical Centre for Giant Molecules, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
C Corresponding author. Email: mterada@m.tohoku.ac.jp
Australian Journal of Chemistry 67(7) 1124-1128 https://doi.org/10.1071/CH14195
Submitted: 1 April 2014 Accepted: 1 May 2014 Published: 3 June 2014
Abstract
Uncharged chiral bis(guanidino)iminophosphorane organosuperbase catalysts substituted by bulky aryl groups were synthesized. The synthetic procedure for the 7,7-membered spiro-cyclization step was modified to enhance the chemical yield of bis(guanidino)iminophosphorane derived from (1S,2S)-1,2-diphenyl-1,2-ethanediamine. In accordance with the amended procedure, bis(guanidino)iminophosphoranes with bulky aryl substituents were newly synthesized and evaluated as chiral organosuperbase catalysts in the enantioselective amination of 2-methyltetralone.
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[11] CCDC 994562 ((M)-1a), CCDC 994431 ((P)-1a), and CCDC 994563 ((P)-1c) contain the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre (CCDC) via www.ccdc.cam.ac.uk/data_request/cif (2014/March/31).
[12] In order to confirm the conformational symmetry of (M)-1a·HBr and (P)-1a·HBr in solution, we conducted a low-temperature 1H NMR analysis of these salts. Significant broadening of N–H protons and protons at the benzylic position of DPEN was observed in (P)-1a·HBr. In contrast, low-temperature NMR analysis of (M)-1a·HBr exhibited no great change in the shape of peaks compared with that at room temperature. These observations strongly suggest that (P)-1a·HBr possesses an unsymmetrical conformation (C1-symmetry) even in solution, although rapid conformational change would take place, whereas (M)-1a·HBr possesses a C2-symmetric structure as observed in the crystalline state. See Supplementary Material for details.
