The Pd-catalyzed C–H arylation of heterocycles with aryl halides is a straightforward and more environmentally-friendly route to the synthesis of well-defined, pi-conjugated polymers for challenging applications in electronic devices. Although this type of transformation is more atom efficient than crosscouplings, it still poses environmental issues in the form of reaction media and the use of phosphine ligands. A procedure for the C–H arylation of thiophenes, with a substantially improved environmental impact, and a promising application of this protocol to the synthesis of regioregular polythiophenes are reported in this work. g-Valerolactone (GVL), a non-toxic biomass-derived solvent, has been used in this phosphine-free microwave-assisted process and replaces commonly used dipolar aprotic media. Activated aryl bromides gave arylthiophenes in good yields, while iodides were used and pivalic acid was added when electron-withdrawing groups were present. The reaction was also extended to C–H (hetero)arylation polycondensation and a high molecular weight poly(3-hexyl)thiophene was obtained, using low Pd loading, in high yields and good regioregularity in short reaction times. Computational studies have shed light on GVL’s role as a ligand in the catalytic system.

Microwave-assisted, ligand-free, direct C–H arylation of thiophenes in biomass-derived γ-valerolactone

TABASSO, Silvia;CALCIO GAUDINO, Emanuela;CRAVOTTO, Giancarlo
2017-01-01

Abstract

The Pd-catalyzed C–H arylation of heterocycles with aryl halides is a straightforward and more environmentally-friendly route to the synthesis of well-defined, pi-conjugated polymers for challenging applications in electronic devices. Although this type of transformation is more atom efficient than crosscouplings, it still poses environmental issues in the form of reaction media and the use of phosphine ligands. A procedure for the C–H arylation of thiophenes, with a substantially improved environmental impact, and a promising application of this protocol to the synthesis of regioregular polythiophenes are reported in this work. g-Valerolactone (GVL), a non-toxic biomass-derived solvent, has been used in this phosphine-free microwave-assisted process and replaces commonly used dipolar aprotic media. Activated aryl bromides gave arylthiophenes in good yields, while iodides were used and pivalic acid was added when electron-withdrawing groups were present. The reaction was also extended to C–H (hetero)arylation polycondensation and a high molecular weight poly(3-hexyl)thiophene was obtained, using low Pd loading, in high yields and good regioregularity in short reaction times. Computational studies have shed light on GVL’s role as a ligand in the catalytic system.
2017
41
17
9210
9215
microwave, thiophene, gammavalerolactone, biomass
Tabasso, Silvia; Calcio Gaudino, Emanuela; Rinaldi, Laura; Ledoux, Audrey; Larini, Paolo; Cravotto, Giancarlo
File in questo prodotto:
File Dimensione Formato  
NJC 2017-revised.docx

Open Access dal 22/08/2018

Tipo di file: POSTPRINT (VERSIONE FINALE DELL’AUTORE)
Dimensione 3.85 MB
Formato Microsoft Word XML
3.85 MB Microsoft Word XML Visualizza/Apri
C7NJ01540B.pdf

Accesso riservato

Tipo di file: PDF EDITORIALE
Dimensione 1.24 MB
Formato Adobe PDF
1.24 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/1647040
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 17
  • ???jsp.display-item.citation.isi??? 15
social impact