Synlett 2019; 30(16): 1886-1890
DOI: 10.1055/s-0039-1690676
letter
© Georg Thieme Verlag Stuttgart · New York

Synthesis of a Contrapositionally Substituted Cyclohexa-meta-phenylene: A Ready-to-Use Precursor for Cyclohexa-meta-phenylene-Based Materials

Ifzan Arshad
a  Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan   Email: aamersaeed@yahoo.com
b  CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China (USTC), JinZhai Road, Hefei, Anhui Province 230026, P. R. of China   Email: arshadmi@mail.ustc.edu.cn
,
Aamer Saeed
a  Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan   Email: aamersaeed@yahoo.com
,
Pervaiz Ali Channar
a  Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan   Email: aamersaeed@yahoo.com
,
Syeda Aaliya Shehzadi
c  Sulaiman Bin Abdullah Aba Al-Khail-Centre for Interdisciplinary Research in Basic Sciences (SA-CIRBS) International Islamic University, Islamabad, Pakistan
,
Rana Muhammad Irfan
d  Department of Chemistry, Mianwali Campus, University of Sargodha, Sargodha 40100, Pakistan
› Author Affiliations
This work was supported by the Higher Education Commission of ­Pakistan.
Further Information

Publication History

Received: 06 August 2019

Accepted after revision: 25 August 2019

Publication Date:
05 September 2019 (online)


Abstract

A contrapositionally substituted derivative of cyclohexa-meta-phenylene ([6]CMP) was synthesized by an intramolecular Yamamoto coupling reaction of an appropriate terphenyl unit containing a trimethylsilyl substituent. Iododesilylation of the trimethylsilyl groups of the product with iodine monochloride was used to incorporate iodo groups, an important functionality for metal-catalyzed coupling reactions. The iodo groups were also converted into a (pinacolato)boryl groups, another important functionality for coupling reactions. The diborylated [6]CMP is expected to be a versatile potential comonomer and a precursor for the synthesis of CMP-based materials. The synthetic route to the disubstituted [6]CMP included lithiation, Pd-catalyzed borylation, Suzuki coupling, and Yamamoto coupling. The structure of the product was established by NMR spectroscopy and mass spectrometry.

Supporting Information

 
  • References and Notes

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  • 8 (3,3′′-Dibromo-[1,1′:3′,1′′-terphenyl]-5′-yl)(trimethyl)silane (3)Argon was bubbled through a solution of the diborylated derivative 2 (1 g, 2.48 mmol, 1 equiv), 1,3-dibromobenzene (2.92 g, 12.43 mmol, 5 equiv), and K2CO3 (1.46 g, 15 mmol, 5 equiv) in 3:2:1 toluene–EtOH–H2O. Pd(PPh3)4 (71 mg, 2.5 equiv) was added, and the mixture was stirred at 90 °C for 24 h. The organic phase was separated, washed with H2O, dried (MgSO4), and concentrated. The residue was purified by column chromatography (silica gel, hexane; Rf  = 0.50) to give a colorless powder; yield: 0.92 g (81%); mp 230 °C.1H NMR (400 MHz, CDCl3) δ = 7.76 (t, J = 1.7 Hz, 2 H), 7.66 (s, 3 H), 7.56 (dd, J = 1.7, 1.1 Hz, 1 H), 7.54 (dd, J = 1.7, 1.1 Hz, 1 H), 7.52 (dd, J = 1.9, 1.0 Hz, 1 H), 7.50 (dd, J = 1.9, 1.0 Hz, 1 H), 7.33 (t, J = 7.8 Hz, 2 H), 0.36 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ = 143.9, 143.0, 138.1, 133.8, 132.9, 132.0, 128.0, 127.4, 125.9, 121.5, 1.2.
  • 9 15,45-Bis(trimethylsilyl)cyclohexa-meta-phenylene (4)2,2′-bipyridine (312 mg, 2.0 mmol), cod (216 mg, 2.0 mmol), and [Ni(cod)2] (550 mg, 2.0 mmol) were placed in a well-dried Schlenk flask and dissolved in anhyd DMF (80 mL). The mixture was then stirred for 30 min at 80 °C in darkness. A solution of the dibromo compound 3 (500 mg, 1.08 mmol) in degassed anhyd toluene (150 mL) was added quickly, and the resulting mixture was stirred at 80 °C for 3 d. The reaction was stopped by adding 10% aq HCl, and the organic phase was separated, washed with H2O, dried (MgSO4) and concentrated in vacuo. The residue was purified by column chromatography [silica gel, PE–CH2Cl2 (20:1); Rf  = 0.29] to give a colorless crystalline solid; yield: 397 mg (61%, 0.66 mmol).1H NMR (400 MHz, CDCl3) δ = 8.34 (s, 4 H), 8.31 (s, 2 H), 7.86 (d, J = 1.7 Hz, 4 H), 7.75 (t, J = 8.8 Hz, 8 H), 7.58 (t, J = 7.6 Hz, 4 H), 0.39 (s, 18 H).
  • 10 15,45-Bis(pinacolatoboryl)cyclohexa-meta-phenylene (6)A 50 mL flask containing the diiodo compound 5 (1.0 g, 2.1 mmol), bis(pinacolato)diborane (1.42 g, 5.6 mmol), KOAc (2.06 g, 21 mmol), and Pd(dppf)Cl2 (73.2 mg, 0.1 mmol) was evacuated and refilled with argon three times. DMF (30 mL) was then transferred into the flask from a syringe under argon at r.t., and the mixture was stirred at 110 °C for 48 h. The crude product was purified by column chromatography [silica gel, PE–CH2Cl2 (4:1)] to give a white solid; yield: 0.8 g (58%).1H NMR (400 MHz, CDCl3) δ = 8.19 (d, J = 1.7 Hz, 6 H), 7.84 (d, J = 8.7 Hz, 4 H), 7.73 (d, J = 7.1 Hz, 8 H), 7.56 (t, J = 7.7 Hz, 4 H), 1.41 (s, 24 H).