Synthesis of 3‐Aryl Substituted Triimidazotriazines via Regioselective Direct Arylation

A general and convenient selective direct arylation of the 3‐position of triimidazo[1,2‐a:1’,2’‐c:1’’,2’’‐e][1,3,5]triazine (1) with (hetero)aryl halides in DMA was successfully achieved in the presence of K2CO3 as the base and a catalyst precursor consisting of Pd(OAc)2 and P(2‐furyl)3. Electron‐poor and ‐rich (hetero)aryl moieties, including the strongly deactivated and sterically encumbered 2,4,6‐trimethoxyphenyl unit, are well tolerated in the electrophilic partner. The data obtained in this synthetic study support a reaction mechanism involving an electrophilic attack of an arylpalladium‐(II) halide species onto the triazine ring. A selective palladium‐catalyzed direct Csp2‐H arylation of triimidazo[1,2‐a:1’,2’‐c:1’’,2’’‐e][1,3,5]triazine with (hetero)aromatic halides enables the high‐yield synthesis of a variety of 3‐aryltriazines. While (hetero)arylbromides result effective for the C‐3 functionalization with electron‐poor groups, aryl iodides are required for obtaining triazines bearing electron‐rich aryl moieties. Experimental evidence suggests a base‐promoted electrophilic palladation (SEAr) mechanism for the activation of Csp2‐H bond.