Novel 5-(4-alkoxyphenyl)thieno[3,2-b]thiophene-2-carboxylate esters: Highly efficient synthesis and mesogenic evaluation of a new class of materials exhibiting the smectic C phase

Abstract

A series of alkyl 5-(4-alkoxyphenyl)thieno[3,2-b]thiophene-2-carboxylates were prepared via a direct, efficient Pd(0)-catalysed Suzuki–Miyaura coupling approach. A series of long-chain alkyl thieno[3,2-b]thiophene-2-carboxylate esters, synthesised from newly reported alkyl mercaptoacetates, were elaborated into the target compounds via regioselective (C-5) halogenation followed by cross-coupling with 4-alkoxyphenyltrifluoroborate salts. As expected, these target alkyl 5-(4-alkoxyphenyl)thieno[3,2-b]thiophene-2-carboxylate ester mesogens exhibited the orthogonal smectic A phase; notably, they are the first materials built on the thieno[3,2-b]thiophene motif to also exhibit the smectic C mesophase.

Keywords:

• esters
• organotrifluoroborates
• smectic C
• thieno[3,2-b]thiophene

Acknowledgements

Financial support through Kent State University (KSU), a Research Incentive Grant from the Ohio Board of Regents (OBR), and KSU's REU-NSF program is gratefully acknowledged. The authors also thank Dr Robert J. Twieg for the use of his DSC instrument and Dr Mahinda Gangoda for help in the acquisition of some NMR spectra.