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3. For P-stereogenic bis- or poly-(diarylphosphino)-containing ligands, see: (a)
Johnson, C. R.; Imamoto, T. J. Org. Chem. 1987, 52, 2170–2174; (b) Imamoto, T.;
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of DiPAMP. Their screening in the Rh(I)-catalyzed hydrogenation of
-acetamidostyrene identified the P-(2-MeO-3-naphthyl)-substi-
a
tuted ligand which led to 90% ee coupled with 2.5-fold shorter
reaction time under mild conditions (1 bar H2, rt). In addition, this
study revealed that for this substrate, substitution on position 3 of
the P-o-anisyl rings is detrimental while it is beneficial on position
5. It seems that an increased steric effect on position 3 has a neg-
ative effect on enantioselectivity, while substituents on position 5
can exert an increase in enantioselectivity due to electronic rea-
sons. Catalysis continues to be a very sensitive function of ligand
structure and key challenges remain associated with the complex-
ity of rational design of an optimum ligand. The P-(2-MeO-3-naph-
thyl) groups of the ligand increase its overall steric requirements
and we believe that they induce a favored conformation of its
Rh(I) complex which may facilitate the turnover-limiting and
enantiodetermining H2 oxidative-addition step. Nevertheless, cau-
tion should be exercised in extrapolation of these results to other
ˇ ˇ
Angew. Chem., Int. Ed. 2007, 46, 4141–4144; (p) Zupancic, B.; Mohar, B.;
Stephan, M. Adv. Synth. Catal. 2008, 350, 2024–2032.
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Org. Chem. 2007, 72, 8010–8018.
a
-acetamidostyrenes as changes in a substrate structure could
necessitate other requirements/matching for the catalyst.11 Ongo-
ing progress in our group in this area shall be communicated in due
time.
5. For (RP,SC)-TangPhos ((RP,SC)-1,10-di-t-butyl-[2,20]-diphospholane), see: (a)
Tang, W.; Zhang, X. Angew. Chem., Int. Ed. 2002, 41, 1612–1614; (b) Tang, W.;
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Acknowledgments
6. For (S,S)-R-BisP* series ((S,S)-1,2-bis(alkylmethylphosphino)ethanes) and (R,R)-
R-MiniPHOS series ((R,R)-1,2-bis(alkylmethylphosphino)methanes), see: (a)
Yamanoi, Y.; Imamoto, T. J. Org. Chem. 1999, 64, 2988–2989; (b) Gridnev, I. D.;
Higashi, N.; Asakura, K.; Imamoto, T. J. Am. Chem. Soc. 2000, 122, 7183–7194; (c)
Gridnev, I. D.; Yamanoi, Y.; Higashi, N.; Tsurata, H.; Yasutake, M.; Imamoto, T.
Adv. Synth. Catal. 2001, 343, 118–136; (d) Gridnev, I. D.; Yasutake, M.; Higashi,
N.; Imamoto, T. J. Am. Chem. Soc. 2001, 123, 5268–5276.
This work was supported by the Ministry of Higher Education,
Science, and Technology of the Republic of Slovenia (Grant J1-
9806), and by the Ministry of National Education, Research, and
Technology of France (Grant 00P141 to PhosPhoenix SARL).
7. Landis, C. R.; Halpern, J. J. Am. Chem. Soc. 1987, 109, 1746–1754.
8. A series of closely related analogs of DiPAMP were prepared with different
substitution patterns on the P-o-An groups with substituents such as: MeO,
TMS, tBu, Ph, or a fused benzene ring. For this, see Ref. 3p.
Supplementary data
9. For phosphines, see: (a) Burk, M. J.; Wang, Y. M.; Lee, J. R. J. Am. Chem. Soc. 1996,
118, 5142–5143; (b) Burk, M. J.; Casy, G.; Johnson, N. B. J. Org. Chem. 1998, 63,
6084–6085; (c) Zhang, Z.; Zhu, G.; Jiang, Q.; Xiao, D.; Zhang, X. J. Org. Chem.
1999, 64, 1774–1775; (d) Lee, S.-G.; Zhang, Y. J.; Song, C. E.; Lee, J. K.; Choi, J. H.
Angew. Chem., Int. Ed. 2002, 41, 847–849; For phosphites, see: (e) Huang, H.;
Zheng, Z.; Luo, H.; Bai, C.; Hu, X.; Chen, H. J. Org. Chem. 2004, 69, 2355–2361;
For phosphoramidites, see: (f) Hu, A.-G.; Fu, Y.; Xie, J.-H.; Zhou, H.; Wang, L.-X.;
Zhou, Q.-L. Angew. Chem., Int. Ed. 2002, 41, 2348–2350; (g) Jia, X.; Li, X.; Xu, L.;
Shi, Q.; Yao, X.; Chan, A. S. C. J. Org. Chem. 2003, 68, 4539–4541; (h) Hu, X.-P.;
Zheng, Z. Org. Lett. 2004, 6, 3585–3588; (i) Bernsmann, H.; van den Berg, M.;
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Org. Chem. 2005, 70, 943–951; (j) Liu, Y.; Ding, K. J. Am. Chem. Soc. 2005, 127,
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Supplementary data (experimental procedures and characteriza-
tion data for all new compounds) associated with this article can be
References and notes
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11. For example, hydrogenation of
a
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a
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