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.