Synthesis and photophysical properties of tetra- and pentaalkynylfluorobenzenes by Sonogashira reactions of novel iodofluorobenzenes

doi:10.1016/j.tet.2012.10.049

Tetrahedron

Volume 69, Issue 1, 7 January 2013, Pages 174-183

https://doi.org/10.1016/j.tet.2012.10.049 Get rights and content

Abstract

1,2-Difluoro-3,4,5,6-tetraiodobenzene, 1,3-difluoro-2,4,5,6-tetraiodobenzene, 1,4-difluoro-2,3,5,6-tetraiodobenzene and 1-fluoro-2,3,4,5,6-pentaiodobenzene were prepared by oxidative iodination of fluorinated benzenes. Sonogashira cross-coupling reactions of these fluorinated periodobenzenes afforded fluorescent penta- and tetraalkynylfluorobenzenes in high yields.

Graphical abstract

Introduction

Polyalkynylated carbon rich molecules are of considerable importance as liquid crystals,¹ non-linear optical materials,² light-emitting materials³ and building blocks for two-dimensional carbon networks.1(a), 4 Light emitting materials have been applied in biological and material sciences, such as FET (field effect transistors), OLED (organic light emitting devices), photovoltaic cells and 3D-optical memory devices.⁵ Extended π-systems of alkynes often give rise to extraordinary electronic and optical changes of the molecule.⁶ In this context, star-shaped π-conjugated molecules with C₆ and C₃ symmetries have attracted considerable attention.⁷ D_6h-symmetric hexaethynylbenzenes and related compounds have been used as core structures for dendritic materials,⁸ and functional dyes.⁹ Recently, hexaethynylbenzene derivatives have also been employed as building blocks for supramolecular architectures¹⁰ and potential nonlinear optical materials for two-photon absorption (TPA) and third-order optical nonlinearity.3, 11 Functionalized hexa(arylethynyl)-benzenes have been synthesized by different synthetic approaches.¹² Hexaalkynylbenzenes of C_2v symmetry have been prepared by Diels–Alder reaction of tetraalkynylcyclopentadienones with alkynes.¹³ A method for the synthesis of hexaalkynylbenzenes of D_3h symmetry was developed by Rubin.¹⁴ Recently, Anthony et al. reported the synthesis of a D_2h symmetric hexaalkynylbenzene from tetrabromo-benzoquinone.¹⁵ Vollhardt et al. reported the synthesis of hexaalkynylbenzenes and their application to the synthesis of archimedanes.¹⁶

The fluorine atom has a strong electronic influence on aromatic compounds. Despite the importance of fluorinated arenes in medicinal chemistry and material sciences,17, 18 peralkynylated fluorobenzenes have, to the best of our knowledge, not been reported so far. Herein, we report the synthesis of four novel hexahalobenzenes, i.e., 1,2-difluoro-3,4,5,6-tetraiodo-benzene, 1,3-difluoro-2,4,5,6-tetraiodobenzene, 1,4-difluoro-2,3,5,6-tetraiodobenzene and 1-fluoro-2,3,4,5,6-pentaiodobenzene. Despite their structural simplicity, only fluoropentaiodobenzene has been previously reported and fully characterized. Although all four compounds represent very interesting synthetic building blocks, their chemistry has, to the best of our knowledge, not been studied so far. Herein, we report Sonogashira reactions of these molecules, which allow for a convenient synthesis of hitherto unknown fluorescent tetra- and pentaalkynylfluorobenzenes.

Section snippets

Results and discussion

1,2-Difluoro-3,4,5,6-tetraiodobenzene (1), 1,3-difluoro-2,4,5,6-tetraiodobenzene (3), 1,4-difluoro-2,3,5,6-tetraiodobenzene (5) and 1-fluoro-2,3,4,5,6-pentaiodobenzene (7) were prepared in very good yields by potassium persulfate mediated periodination of 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene and fluorobenzene, respectively (Scheme 1). The reactions were carried out using the method recently developed by Rahman et al.¹⁹ The synthesis and characterization of 7 has been

General

¹H NMR spectroscopy: Bruker: AM 250, Bruker ARX 300, Bruker ARX 500; δ=0.00 ppm for tetramethylsilane; δ=7.26 ppm for (CDCl₃); Characterization of the signal fragmentations: s=singlet, d=doublet, dd=double of doublet, t=triplet, q=quartet, m=multiplet, br=broadly. All coupling constants are indicated as (J). 2D NMR techniques (NOESY, COSY, HMQC and HMBC) were used for the confirmation of structure. ¹³C NMR Spectroscopy: Bruker: AM 250, (62.9 MHz); Bruker: ARX 300, (75 MHz), Bruker: ARX 500,

Acknowledgements

Financial support by the DAAD, by the State of Pakistan and by the State of Mecklenburg-Vorpommern (scholarships for M.S.) and by the University of Rostock (INF scholarship for S.R.) is gratefully acknowledged. The work was also supported by the TÁMOP-4.2.1/B-09/KONV-2010-007 project. The project is implemented through the New Hungary Development Plan, co-financed by the European Social Fund and the European Regional Development Fund.

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Synthesis and photophysical properties of tetra- and pentaalkynylfluorobenzenes by Sonogashira reactions of novel iodofluorobenzenes

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

General

Acknowledgements

Chem. Soc. Rev.

Nature

Liq. Cryst.

Angew. Chem., Int. Ed.

J. Chem. Soc., Chem. Commun.

Org. Lett.

Chem.—Eur. J.

Synlett

Liq. Cryst.

Org. Lett.

Angew. Chem., Int. Ed.

Chem. Rev.

J. Mater. Chem.

Adv. Mater. (Weinheim, Ger.)

Science

Science

J. Am. Chem. Soc.

Liq. Cryst.

J. Org. Chem.

J. Am. Chem. Soc.

Organometallics

Chem. Lett.

Chem.—Eur. J.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

ChemPhysChem

Chem.—Eur. J.