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Synlett 2007(12): 1969-1971  
DOI: 10.1055/s-2007-982567
LETTER
© Georg Thieme Verlag Stuttgart · New York

Stereoselective Cross-Coupling Reaction of 2,4-Diaryl-1,1-diboryl-1,3-butadienes: Stereocontrolled Approach to 1,3,4,6-Tetraarylated 1,3,5-Hexatrienes

Masaki Shimizu*, Katsuhiro Shimono, Michael Schelper, Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
Fax: +81(75)3832445; e-Mail: shimizu@npc05.kuic.kyoto-u.ac.jp;
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Publication History

Received 7 April 2007
Publication Date:
25 June 2007 (online)

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Abstract

The boryl group cis to the C(3)=C(4) group in 2,4-aryl-1,1-bis(pinacolatoboryl)-1,3-butadienes undergoes Pd-catalyzed cross-coupling reaction with aryl iodides stereoselectively at room temperature, giving rise to the corresponding boronates as a single diastereomer. Subsequent coupling of the boronates with alkenyl ­iodides allows us to synthesize 1,3,4,6-tetraarylated 1,3,5-hexa­trienes stereoselectively.

Key words

alkenes - boron - cross-coupling - palladium - stereoselectivity

    References and Notes

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4

Typical Procedure
A solution of 1a (0.10 g, 0.22 mmol), iodobenzene (47 mg, 0.23 mmol), Pd(PPh3)4 (13 mg, 0.011 mmol), and 3 M KOH aq (0.22 mL, 0.65 mmol) in THF (5 mL) was stirred at r.t. for 8 h before quenching with sat. aq NH4Cl (20 mL). The aqueous layer was extracted with EtOAc (3 × 20 mL), washed with sat. NaCl aq (20 mL), and dried over anhyd MgSO4. Removal of the organic solvents in vacuo followed by PTLC (hexane-EtOAc, 10:1) gave 2a (72 mg, 76% yield) as a colorless solid; mp 98.0 °C. 1H NMR (400 MHz, CDCl3): δ = 1.00 (s, 12 H), 6.22 (d, J = 16.0 Hz, 1 H), 7.21-7.41 (m, 15 H). 13C NMR (67.8 MHz, CDCl3): δ = 24.4, 83.4, 126.5, 126.5, 126.7, 127.3, 127.6, 127.9, 128.1, 128.5, 128.8, 129.5, 130.2, 134.2, 137.4, 140.4, 141.6, 148.5. IR (KBr): 3051, 3023, 2976, 2928, 2362, 2343, 1952, 1730, 1595, 1576, 1491, 1442, 1360, 1308, 1267, 1213, 1142, 1074, 1024, 974, 859, 752, 700, 579 cm-1. MS (EI, 70 eV): m/z (%) = 409 (21) [M+ + 1], 408 (71) [M+], 280 (100). HRMS: m/z calcd for C28H29BO2 [M+]: 408.2261; found: 408.2268. Anal. Calcd for C28H29BO2: C, 82.36; H, 7.16. Found: C, 82.34; H, 7.16.

5

Crystal data of 2a and 3a are deposited at Cambridge Crystallographic Data Centre as CCDC-619246 and CCDC-619193.

7

Typical Procedure
A solution of 2a (10 mg, 0.023 mmol), β-iodostyrene (8.0 mg, 0.035 mmol), Pd[P(t-Bu)3]2 (1.0 mg, 1.8 µmol, 8 mol%) and 3 M aq KOH solution (23 µL, 0.069 mmol) in THF (1 mL) was stirred at 60 °C for 12 h before quenching with sat. aq NH4Cl solution (10 mL). The aqueous layer was extracted with EtOAc (3 × 10 mL), washed with sat. aq NaCl solution (10 mL). The organic layer was separated, dried over anhyd MgSO4, and concentrated in vacuo. The residue was purified by preparative TLC (hexane-EtOAc, 10:1) to give 3a (8.5 mg, 96% yield) as a 95:5 mixture of 1E,3E,5E- and 1Z,3Z,5E-isomers as a pale yellow solid. The recrystallization of the mixture from hexane gave (1E,3E,5E)-3a; mp 173.1 °C (hexane). R f = 0.63 (hexane-EtOAc, 10:1). 1H NMR (400 MHz, CDCl3): δ = 6.07 (d, J = 16.0 Hz, 2 H), 6.92 (d, J = 16.0 Hz, 2 H), 7.10-7.53 (m, 20 H). 13C NMR (100 MHz, CDCl3): δ = 126.5, 127.3, 127.4, 128.3, 128.5, 130.4, 130.8, 132.4, 137.6, 138.9, 141,0. IR (KBr): 3030, 1595, 1574, 1489, 1442, 1315, 1146, 1070, 1024, 961, 908, 750, 704, 689, 577, 556, 525 cm-1. MS (EI, 70 eV): m/z (%) = 386 (7) [M+ + 2], 385 (31) [M+ + 1], 384 (100) [M+]. HRMS: m/z calcd for C30H24 [M+]: 384.1878; found: 384.1880. Anal. Calcd for C30H24: C, 93.71; H, 6.29. Found: C, 93.72; H, 6.53.