Synlett 2005(15): 2337-2341  
DOI: 10.1055/s-2005-872666
LETTER
© Georg Thieme Verlag Stuttgart · New York

Functionalized Heptahelicene Bidentate Ligands and Chiral Building Blocks

Marc Gingras*, Christine Collet
Chemical Laboratory of Organic and Inorganic Materials (CMOM), Faculty of Sciences, University of Nice-Sophia Antipolis, 28 Av. Valrose, 06700 Nice Cedex 2, France
Fax: +33(4)92076578; e-Mail: gingras@unice.fr;
Further Information

Publication History

Received 12 June 2005
Publication Date:
07 September 2005 (online)

Abstract

Syntheses of functionalized heptahelicenes 11-13 disubstituted at positions 3 and 16 by hydroxymethyl or bromomethyl functions are described as a new series of bidentate ligands or chiral building blocks. Those functions are flexible enough and properly positioned for a possible chelate effect onto a metal center. Photocyclodehydrogenation, phase-transfer-catalyzed Wittig reaction, and use of THP groups for increasing solubility and further functional group transformations were key elements in this synthetic route.

1

Former address: Organic Chemistry Division, Laboratory of Supramolecular Chemistry and Catalysis, Faculty of Sciences, Université Libre de Bruxelles, C.P. 160-06, 50 Ave. F. D. Roosevelt, 1050 Brussels, Belgium.

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Synthesis of Bis(stilbene) 9. At 20 °C, aldehyde 8 (2.658 g, 9.84 mmol) was dissolved in CH2Cl2 (50 mL), followed by addition of phosphonium salt 3 (4.266 g, 4.92 mmol) and an aq solution of 5 M KOH (50 mL). After vigorous stirring for 15 h, the organic layer was separated and dried over anhyd MgSO4. After filtration and evaporation of the solvent, the expected bis(stilbene) was purified on a SiO2 flash chromatography column using CH2Cl2-MeOH (98:2) as eluent. Bis(stilbene) (9) was obtained as a solid (isomeric mixture, 2.85g. 4.13 mmol, 84% yield). 1H NMR (250 MHz, CDCl2CDCl2, isomeric mixture): δ = 1.40-2.00 (m, 12 H, CH2), 3.40-3.60 (m, 2 H, CH2-O), 3.85-4.00 (m, 2 H, CH2-O), 4.50-4.75 (m, 4 H, naphthyl-CH2, O-CH-O), 4.85-5.00 (m, 2 H,), 6.90-7.30 (m, 2 H, CH=CH), 7.40-8.00 (m, 16 H, H arom.), 8.26 (s, 1 H, H arom. CH=CBr). 13C NMR (62.9 MHz, CDCl2CDCl2, isomeric mixture): δ = 19.4 (CH2), 25.4 (CH2), 30.6 (CH2), 62.2 (CH2-O), 68.7 (CH2-O), 97.9 (O-CH-O), 123.0 (CH arom.), 123.70-139.83 (multiple signals from an isomeric mixture). MS (EI, 70 eV): m/z (%) = 690 (3.4) [M+ (81Br)], 688 (3.2) [M+ (79Br)], 606 (13) [M+ (81Br) - C5H8O], 604 (14) [M+ (79Br) - C5H8O], 522 (88) [M+ (81Br) - C10H16O2], 520 (100) [M+ (79Br) - C10H16O2]. HRMS (EI, 70 eV): m/z (%) = 690.2193 [M+ (81Br), exp.; 690.2168 calcd], 688.2192 [M+ (79Br), exp.; 688.2188 calcd], 522.1004 [M+ (81Br) - C10H16O2, exp.; 522.1017 calcd], 520.0999 [M+ (79Br) - C10H16O2, exp.; 520.1038 calcd].

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Photocyclodehydrogenation Procedure to 10.
In a photochemical reactor equipped with a water cooling jacket and a stir bar, compound 9 (0.420 g, 0.609 mmol), iodine (309 mg, 1.22 mmol) and 1,2-epoxybutane (8.0 mL) were dissolved in high purity grade benzene (700 mL). Nitrogen gas was bubbled through the solution within 30 min while stirring vigorously for removing oxygen prior to irradiation with a high-pressure mercury lamp for 3 h. When the reaction was complete, excess of iodine was reduced with a 15% aqueous solution of Na2S2O3 (20 mL). The aqueous phase was separated and the organic layer dried over MgSO4. After filtration and evaporation of solvent, the crude was purified by flash chromatography on silica gel with CH2Cl2-EtOAc (98:2) and then (95:5). Helicene 10 was obtained as a yellow solid (0.270 g, 0.393 mmol, 65% yield). 1H NMR (250 MHz, CDCl2CDCl2): δ = 1.40-2.00 (m, 12 H, CH2), 3.50 (m, 2 H, CH2-O), 3.85 (m, 2 H, CH2-O), 4.36 (d, J = 12.4 Hz, 2 H, naphthyl-CH2), 4.52 (m, 4 H, O-CH-O, naphthyl-CH2), 6.39 (d, J = 7.0 Hz, 1 H, H arom.), 6.42 (d, J = 7.7 Hz, 1 H, H arom.), 6.98 (d, J = 7.3 Hz, 2 H, H arom.), 7.22 (s, 1 H, H arom.), 7.24 (s, 1 H, H arom), 7.70 (d, J = 8.8 Hz, 1 H, H arom.), 7.74 (d, J = 8.8 Hz, 1 H, H arom.), 7.40-7.50 (m, 2 H, H arom.), 7.87 (d, J = 8.0 Hz, 1 H, H arom.), 7.92 (d, J = 8.0 Hz, 1 H, H arom.), 7.99 (d, J = 8.8 Hz, 1 H, H arom.), 8.32 (s, 1 H, H arom. CH=CBr), 8.42 (d, J = 8.4 Hz, 1 H, H arom.). 13C NMR (62.9 MHz, CDCl2CDCl2, DEPT): δ = 19.3 (CH2), 25.5 (CH2), 30.6 (CH2), 62.0 (CH2O), 67.7 (CH2O), 96.9 (OCHO), 121.1 (C arom.), 123.7 (CH arom.), 123.9 (CH arom.), 124.0 (CH arom.), 124.3 (CH arom.), 124.6 (C arom.), 125.2 (CH arom.), 125.3 (CH arom.), 125.4 (CH arom.), 125.6 (CH arom.), 125.9 (CH arom.), 126.9 (C arom.), 127.4 (CH arom.), 127.6 (C arom.), 127.9 (CH arom.), 128.3 (CH arom.), 128.4 (C arom.), 128.6 (C arom.), 129.9 (CH arom.), 130.2 (C arom.), 130.8 (C arom.), 131.4 (C arom.), 131.5 (C arom.), 131.9 (C arom.), 135.1 (C arom.). MS (EI, 70 eV): m/z (%) = 686 (45) [M+ (81Br)], 684 (43) [M+ (79Br)], 602 (41) [M+ (81Br) - C5H8O], 600(39) [M+ (79Br) - C5H8O], 520 (25) [M+ (81Br) - 2OTHP], 518 (30) [M+ (79Br) - 2OTHP]. R f = 0.42 (TLC, SiO2, CH2Cl2-EtOAc, 98:2).

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9-Bromo-3,16-bis(hydroxymethyl)heptahelicene (11).
Compound 10 (83.2 mg, 0.121 mmol) was added to EtOH (25 mL) as a suspension at 20 °C, followed by p-toluene-sulfonic acid hydrate as catalyst (5.0 mg, 0.0026 mmol). After vigorous stirring for 15 h, the solvent was evaporated and crude diol 11 was purified by flash chromatography on SiO2 with CH2Cl2-EtOAc (80:20) and then pure EtOAc as eluent. Pure diol 11 was obtained (50.1 mg, 0.097 mmol, 80% yield). 1H NMR (250 MHz, DMSO-d 6): δ = 4.35 (4 H, CH2OH), 5.10 (2 H, large, OH), 6.36 (dd, J = 1.1 Hz, J = 8.8 Hz, 2 H, CH), 6.86 (dd, J = 2.2 Hz, J = 8.8 Hz, 2 H, CH), 7.34 (2 H, app. s, CH arom.), 7.61 (1 H, d, J = 8.0 Hz, CH), 7.64 (d, 1 H, J = 8.0 Hz, CH), 7.84 (d, 1 H, J = 8.9 Hz, CH), 7.88 (d, 1 H, J = 9.1 Hz, CH), 8.10 (s, 2 H, CH arom.), 8.18 (d, 1 H, J = 8.4 Hz, CH), 8.35 (d, 1 H, J = 8.4 Hz, CH), 8.57 (s, 1 H, CH arom.). 13C NMR (62.9 MHz, DMSO-d 6, DEPT): δ = 62.4 (CH2OH), 120.3 (C), 122.6 (CH), 123.1 (CH), 123.5 (CH), 124.1 (C), 124.6 (CH), 125.4 (CH arom.), 125.6 (CH), 125.7 (CH), 126.5 (C), 127.5 (C), 127.7 (C), 127.9 (CH), 128.4 (CH), 128.7 (CH), 128.8 (CH), 129.4 (C), 129.9 (CH), 130.5 (C), 130.6 (C), 131.6 (C), 131.7 (C), 139.5 (C), 139.6 (C). MS (EI, 70 eV): m/z (%) = 518 (66) [M+ (81Br)], 516 (100) [M+ (79Br)], 374 (60) [M+ - HBr - CH2OH -CH2OH], 187 (51) [C30H14 ++]. R f = 0.05 (TLC, SiO2, CH2Cl2-EtOAc, 4:1).