Diprotodecarboxylation Reactions of 3,4-Dialkoxythiophene-2,5-dicarboxylic Acids Mediated by Ag₂CO₃ and Microwaves

Abstract

An efficient and rapid method is reported to obtain 3,4-dialkoxythiophenes from 3,4-dialkoxythiophene-2,5-dicarboxylic acids through a diprotodecarboxylation reaction with Ag₂CO₃/AcOH as a catalytic system and microwave heating in dimethylsulfoxide (DMSO) as solvent. This methodology lets us obtain for the first time good performance with thiophenes bearing strong electron-donating groups such as alkoxides. This methodology eliminates the usage of harmful quinoline as solvent, as well as the long reaction times typically used (12–18 h) to obtain the 3,4-dialkoxythiophenes. The reaction of 7 diacids showed good yields (60–89%) following 20 min of microwave heating in a temperature range of 120–150 °C.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

GRAPHICAL ABSTRACT

Keywords:

• Ag₂CO₃
• 3,4-dialkoxythiophene-2,5-dicarboxylic 3,4-dialkoxythiophenes
• microwaves
• protodecarboxylation

ACKNOWLEDGMENTS

P. A. C. P. thanks the CONACYT for doctoral fellowship. Funding through PAPIIT Project IN202011 and CONACYT Project 179356 is also acknowleged. Nieves Zavala Segovia, Alejandra Nuñez Pineda, Rubén Gaviño-Ramirez, Isabel Chavez Uribe, Angeles Peña Gonzalez, and Lizbeth Triana Cruz are recognized by their technical support in this work.

Notes

^a In all experiments, 0.5 mmol of diacid was used.

^b With microwave heating (temperature of IR sensor).

^c The acid and catalyst were stirred for 5 min before adding AcOH and start microwave heating.

^d Using 5 mmol.

^a Using 0.5 mmol of compound 1, 1 mmol of AcOH, 40% mol Ag₂CO₃, prestirring of diacid and catalyst, and microwave heating.

^b Main product.