The synthesis, characterization, and structure of a series of 4H-thieno[3,4-c]pyrroles and their corresponding pyrrolium cyanoborohydride salts

Abstract

A general, convenient route toward N-substituted 5,6-dihydro-4H-thieno[3,4-c]pyrroles was accomplished by the reductive amination of 2,5-dimethylthiophene-3,4-dicarbaldehyde with various primary amines in a solution of sodium cyanoborohydride and methanol/acetic acid (80–88% yield). For the N-alkyl cases, the product isolated was the cyanoborohydride salt of the desired product, 1,3-dimethyl-5-alkyl-5,6-dihydro-4H-thieno[3,4-c]-5-pyrrolium cyanoborohydride. For the aryl case employing aniline, the desired free pyrrole, 1,3-dimethyl-5-phenyl-5,6-dihydro-4H-thieno[3,4-c]pyrrole, was isolated. X-ray crystallographic analysis of both the N-propyl and N-phenyl trials confirmed the salt and free amine nature of the products.

GRAPHICAL ABSTRACT

Keywords:

• thiophenes
• pyrroles
• X-ray crystal structure
• ring closure
• cyanoborohydride salt

Acknowledgements

We wish to thank our sources of support for this research, including the Department of Chemistry, the Junior Faculty Summer Research Award from the College of Arts and Sciences and the Chemistry Diversity Initiative at Eastern Kentucky University. We also wish to thank Dr Jay Baltisberger at Berea College in Berea, KY for his support on the NMR spectroscopy.