DFT Studies on Copper-Catalyzed Dearomatization of Pyridine

A systematic theoretical study has been performed with the aid of density functional theory (DFT) calculations on the mechanism of asymmetric 1,4-dearomatization of free pyridine with styrene and dimethoxy­(methyl)­silane (HSiMe­(OMe)2) catalyzed by copper complexes. Two proposed mechanisms, dearomatization of pyridine catalyzed by cooperation of two copper­(I) centers and by one copper­(I), are calculated and analyzed. The results indicate that one copper­(I) center is capable of catalyzing the dearomatization reaction. To achieve the dearomatization on one copper­(I) center, the Cu–H addition “product” (derived from styrene insertion into Cu–H) undergoes 1,3- and 1,5-Cu migration on a benzylic ligand, facilitating the 1,2- and 1,4-dearomatization of pyridine. In the two metal-center mechanism, significant sterically repulsive interactions among the substituents on the ligands between the two metal fragments hindered the dearomatization process. The origin of selectivity between 1,2- and 1,4-dearomatization of pyridine has also been discussed.