Synthesis of 2-(o-hydroxyaryl)-4-arylthiazoles by regioselective Pd(0)- catalyzed cross-coupling

The difunctional substrate 2,4-dibromothiazole 2 was transformed into the title compounds 1 by consecutive Pd(0)-catalyzed cross-coupling reactions. Aryl zinc reagents which were prepared by ortho-lithiation of compounds 3 and subsequent transmetalation were used as carbon nucleophiles in the first coupling reaction. By this means, an aryl substituent was attached to the 2-position (50-62% yield). A succeeding cross-coupling with arylboronic acids 4 occurred at the 4-position of the intermediate 4- bromothiazoles 5 (76-97% yield).