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Synlett 2009(10): 1667-1669  
DOI: 10.1055/s-0029-1217191
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© Georg Thieme Verlag Stuttgart ˙ New York

One-Pot Preparation of Chiral Dinuclear Vanadium(V) Complex

Shinobu Takizawa, Doss Rajesh, Tomomi Katayama, Hiroaki Sasai*
The Institute of Scientific and Industrial Research (ISIR), Osaka University, Mihogaoka, Ibaraki-shi, Osaka 567-0047, Japan
Fax: +81(6)68798469; e-Mail: sasai@sanken.osaka-u.ac.jp;
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Publication History

Received 16 February 2009
Publication Date:
02 June 2009 (online)

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Abstract

A convenient one-pot procedure for the preparation of dinuclear vanadium(V) complex is described. The complex exhibited high catalytic activity for oxidative coupling of 2-naphthol derivatives. In addition, coupling of 9-phenanthrol gave (S)-10,10′-dihydroxy-9,9′-biphenanthryl in quantitative yield with 93% ee.

Key words

oxidative coupling - dinuclear vanadium complex - dual activation - biphenanthrol - asymmetric synthesis

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General Procedure for the One-Pot Preparation of (R a , S , S)-1
A round-bottomed flask was charged with (R)-3,3′-diformyl-2,2′-dihydroxy-1,1′-binaphthyl (2, 500 mg,
1.46 mmol), (S)-tert-leucine (3, 383 mg, 2.92 mmol), VOSO4˙H2O (952 mg, 5.84 mmol), MS 3 Å (1.46 g) and MeOH (50 mL) under O2 (balloon). The reaction mixture was refluxed, and the consumption of 2 was monitored by TLC (acetone-hexane, 1:3). The resulting solution was gradually cooled down to r.t. and filtered through Celite to remove MS 3 Å. The filtrate was evaporated, and the resulting black solid was dissolved in CH2Cl2 and washed with H2O. The organic phase was dried over anhyd Na2SO4 and concentrated in vacuum to give (R a ,S,S)-1 (738 mg, 69%) as a black powder. Compound (R a ,S,S)-1: ¹H NMR (270 MHz, CD3OD): δ = 8.96 (s, 2 H, CH=N), 8.48 (s, 2 H, ArH), 8.06 (t, J = 4.7 Hz, 2 H, ArH), 7.70 (t, J = 4.9 Hz, 2 H, ArH), 7.44-7.38 (m, 4 H, ArH), 4.23 (s, 2 H, CHt-Bu), 1.25 (s, 18 H, t-Bu). ¹³C NMR (67.7 MHz, CD3OD): δ = 167.9, 138.7, 137.6, 130.6, 130.5, 129.6, 127.4, 125.3, 124.1, 83.8, 38.8, 28.2. 5¹V NMR (CD3OD): δ = -557.2. IR: 3436 (OH), 1683 (C=N), 1608 (C=O), 996 (V=O) cm-¹. HRMS-FAB: m/z calcd for C34H35N2O10V2: 733.1171 [M + H]+; found: 733.1185.

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The catalyst 1 prepared by the two-step promoted coupling reaction of 2-naphthol to afford (S)-BINOL with 96% yield and 85% ee in 24 h at r.t. under air.

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Representative Procedure for the Oxidative Coupling of 9-Phenanthrol Using ( R a , S , S )-1 In a round-bottomed flask (500 mL) was taken CH2Cl2 (240 mL) and 9-phenanthrol (5, 6.0 g, 30.9 mmol). Compound (R a ,S,S)-1 (1.1 g, 1.54 mmol) was charged, and the reaction vessel was purged with O2 (balloon). The reaction was stirred for 48 h at -10 ˚C. A short column to remove the catalyst gave (S)-4 in quantitative yield with 90% ee. Single recrystallization of the product thus obtained with hexane-acetone (5:4) gave optically pure (S)-4 in 79% yield.
Compound (S)-4: >99% ee, [α]D ²³ -65.7 (c 1.2, CHCl3).