Synthesis and Solid-State Structures of Dimethyl 2,2‘-Bithiophenedicarboxylates

• Published in: Journal of organic chemistry Vol. 67; no. 20; pp. 6931 - 6937
• Main Authors: Pomerantz, Martin, Amarasekara, Ananda S, Dias, H. V. Rasika
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04-10-2002
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Organic chemistry; Preparations and properties; Substituent effect; Molecular rigidity; Rotation barrier; Five membered ring; Electrostatic effect; Bond length; Molecular structure; Stabilization; Conformational analysis; Bond angle; Theoretical study; Steric hindrance; X ray diffraction; Solid state; Thiophene derivatives; Sulfur heterocycle; Diester; Bicyclic compound; Ab initio calculations; Chemical synthesis; Torsion
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo020307b

The syntheses of dimethyl 2,2‘-bithiophene-4,4‘-dicarboxylate (3), dimethyl 2,2‘-bithiophene-3,4‘-dicarboxylate (4), and dimethyl 2,2‘-bithiophene-3,3‘-dicarboxylate (5) are described. Single-crystal X-ray structural analysis of these compounds shows that the thiophene rings in 3 and 4 are nearly coplanar (dihedral angle close to 0°) and they adopt the anti sulfur conformation in the solid state. Further, the structure of 4 is in agreement with our previous suggestion that there is an electrostatic stabilization of the planar structure due to attraction of the 3-carbonyl oxygen to the sulfur of the distal ring. In 5, however, the thiophene rings are nearly perpendicular (dihedral angle 75°), indicating considerable steric hindrance between the two large ester groups at the 3- and 3‘-positions. Unlike compounds 3 and 4, where the thiophene rings have the sulfur atoms anti, the sulfur atoms in 5 are completely syn. This is the first instance where a bithiophene has been shown to adopt a conformation where the sulfur atoms are completely syn. The solid-state conformations of 3, 4, and 5 are in agreement with ab initio theoretical calculations on these compounds; particularly, the planar conformations of 3 and 4 reflect the previously calculated low rotation barriers of these molecules.