DFT Studies on Copper-Catalyzed Dearomatization of Pyridine
Linlin Wu, Fu Kit Sheong, Zhenyang Lin
Abstract
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.