Improved synthesis of sterically encumbered heteroaromatic biaryls from aromatic β-keto esters

A protocol for the synthesis of hindered 4-aryl 2-aminopyrimidines from β–keto esters is described. The process employs trifluoroethanol as an essential additive to promote the guanidine condensation reaction, enabling the synthesis of 25 aryl- and heteroaryl substituted aminopyrimidines in good yields and high purities with no column chromatography. The conditions described herein are readily scalable and have been employed in the large-scale synthesis of the clinical A2a/A2bR antagonist AB928.