Direct 2-Arylation of Thiophene Using Low Loading of a Phosphine-Free Palladium Catalyst

Abstract

The direct coupling of aryl halides with thiophene would be a considerable advantage for sustainable development because of only HBr associated with a base as by-product is formed and the number of steps to prepare these compounds is less than in more classical coupling reactions. We observed that through the use of only 0.2 mol% Pd(OAc)₂ as the catalyst, a range of aryl bromides undergoes coupling via a C-H bond activation/functionalization reaction with thiophene to give 2-arylated thiophenes in good yields. In most cases, only traces of polyarylated thiophenes were detected when a large excess of thiophene was employed. This air-stable catalyst can be used with a wide variety of aryl bromides.

Keywords:

• Aryl bromides
• catalysis
• C-H activation
• palladium
• thiophene

Notes

^a Conditions: catalyst Pd(OAc)₂ (0.002 mmol), 4-bromobenzonitrile (1 mmol), thiophene (2–10 mmol), KOAc (2 mmol), DMAc (5 mL), 20 h, 130 °C.

^a Conditions: catalyst Pd(OAc)₂ (0.002 mmol), aryl bromide (1 mmol), thiophene (8 mmol), KOAc (2 mmol), DMAc (5 mL), 20 h, 130 °C, isolated yields.

^a Conditions: catalyst PdCl(C₃H₅)(dppb) (0.01 mmol), aryl bromide (1 mmol), thiophene (8 mmol), KOAc (2 mmol), DMAc (5 mL), 20 h, 140 °C, isolated yields.