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DOI: 10.1055/s-2003-37528
Inversion of Planar Chirality vs Axial Isomerization of Axially Chiral Biaryl Chromium Complexes
Publication History
Publication Date:
26 February 2003 (online)
Abstract
syn-Biaryl chromium complexes having a coordinating ortho-substituent gave anti-biaryl chromium complexes 5 with an inversion of the planar chirality by heating in a non-aromatic solvent.
Key words
arene complexes - asymmetric synthesis - atropisomerism - biaryls - isomerizations
- 1
Bringmann G.Walter R.Weirich R. Angew. Chem., Int. Ed. Engl. 1990, 29: 977 -
2a
Kamikawa K.Uemura M. Synlett 2000, 938 -
2b
Kamikawa K.Watanabe T.Uemura M. J. Org. Chem. 1996, 61: 1375 -
2c
Uemura M.Kamikawa K. J. Chem. Soc., Chem. Commun. 1994, 2697 -
2d
Kamikawa K.Watanabe T.Uemura M. J. Synth. Org. Chem. 2001, 59: 1078 - 3
Watanabe T.Shakadou M.Uemura M. Synlett 2000, 1141 - 4 Schmalz et al. reported that the
diastereoeselectivity of direct complexation of 1-tetralol derivatives
with Cr(CO)6 under thermal conditions decreased in longer
reaction time. The decreased diastereoselectivity was explained
by the chromium migration to the inverted arene face under thermal conditions:
Schmalz H.-G.Millies B.Bats JW.Dürner G. Angew. Chem., Int. Ed. Engl. 1992, 31: 631 -
6a
Uemura M.Nishimura H.Kamikawa K.Shiro M. Inorg. Chim. Acta 1994, 222: 63 -
6b
Bringmann G.Göbel L.Peters K.Peters EM.von Schnering HG. Inorg. Chim. Acta 1994, 222: 255 -
8a
The chromium-arene bond is weakened by assistance with the coordinating benzylic oxygen. Tricarbonyl(1-exo-vinyl-1-endo-indanol)chromium complexes were heated in the presence of functionalized arenes, 2-methyl-1,3-cyclopentadione and a catalytic amount of Triton-B to give the corresponding tricarbonylchromium migration products to the existing arenes.
-
8b
Meyer A.Jaouen G. J. Organomet. Chem. 1975, 97: C21 -
8c
Goasmat F.Dabard R.Patin H. Tetrahedron Lett. 1975, 16: 2359 -
9a
A coordinating donor solvent accelerates the ligand exchange.
-
9b
Traylor TG.Stewart KJ. J. Am. Chem. Soc. 1986, 108: 6977 -
9c
Howell JAS.Yates PC.Ashford NF.Dixon DT.Warren R. J. Chem. Soc., Dalton Trans. 1 1996, 3959 -
9d
Kündig EP.Kondratenko M.Romanens P. Angew. Chem. Int. Ed. 1998, 37: 3146
References
General Procedure:
A solution of syn-biaryl complex 3 (0.25 mmol) in mixture of n-Bu2O (2 mL) and (CH2Cl)2 (2 mL)
was stirred at 120 °C for 2 h. The solvent was removed under
reduced pressure, and the residue was purified by silica gel chromatography
to give anti-biaryl complex 5.
Complex 5a: Mp
122 °C. [α]D
31 -142.0
(c 0.1, CHCl3). 1H NMR
(300 MHz, CDCl3): δ = 1.72 (1 H, s,
CH3), 2.09 (3 H, s, CH3), 3.66 (3 H, s, OCH3),
4.20 (2 H, d, J = 5.5
Hz, CH
2
OH),
5.06 (1 H, d, J = 6.5
Hz, Cr-Ar), 5.15 (1 H, d, J = 6.5 Hz, Cr-Ar), 5.79
(1 H, t, J = 6.5
Hz, Cr-Ar), 7.23-7.33 (3 H, m, Ar), 7.42-7.45
(1 H, m, Ar). IR (CHCl3): 1950, 1870, 1530, 1450, 1420,
1260, 1030 cm-1. Anal. Calcd for C18H16O5Cr:
C, 59.34; H, 4.43; Found: C, 59.34; H, 4.50.
Enantiomeric excesses of anti-biphenyl chromium complexes, 4a and 5a were determined by chiral HPLC: Chiralcel OD, hexane/2-propanol (9/1), flow rate 0.5 mL/min, 40 °C, retention time; 13.8 min(4a) and 16.2 min(5a). For racemic 2-methyl-6-hydroxymethyl-2′-biphenyl; chiralcel OJ-H, hexane-2-propanol (50:1), flow rate 0.5 mL/min, 40 °C, retention time; 46.5 min and 53.7 min.