Synthesis of Soai Type 2-Arylpyrimidine-5-carbaldehydes through Desulfurative Cross-Coupling with Arylboronic Acids

A two-step synthesis of 2-arylpyrimidine-5-carbaldehydes, which are of relevance as substrates for Soai's asymmetric autocatalysis, was realized by exploiting a hidden threefold symmetry in the target core structure. Condensation of Arnold's C ₃-symmetric vinamidinium cation with S-methylisothiouronium sulfate provides 2-methylsulfanyl-pyrimidine-5-carbaldehyde; introduction of aryl groups at C-2 of the latter was accomplished by a Liebeskind-Srogl palladium-catalyzed desulfurative (de-methylsulfanylative) coupling with aryl boronic acids to obtain the target compounds 1 (14 examples, 60-95 % yield). 2-Arylpyrimidine-5-carbaldehydes, which are of relevance as substrates in Soai's asymmetric autocatalysis, are prepared through Liebeskind-Srogl coupling of aryl boronic acids with 2-methylthiopyrimidine-5-carbaldehyde; the latter is obtained in a hydrolytic condensation of two symmetric amidinium salts.