Non‐Bonding Electron Pair versus π‐Electrons in Solution Phase Halogen Bond Catalysis: Povarov Reaction of 2‐Vinylindoles and Imines.

The non‐bonding electron pair (n‐pair) of heteroatoms and π‐electrons are both efficient halogen bond (XB) acceptors. In solid and gas phase studies, n‐pairs generally prevail over π‐bonding orbitals as XB acceptors, whereas few studies have been conducted regarding the preference in solution phase. Herein, the Povarov reaction via the C−I⋅⋅⋅N XB interaction and [4+2] cycloaddition via the C−I⋅⋅⋅π XB interaction were evaluated, revealing that the n‐pair was more dominant in the XB catalysis system in solution. The XB donor‐catalyzed Povarov reaction gave diverse indolyl‐tetrahydroquinoline derivatives in good yields. Synthesis of indolyl‐quinolines was also developed. [ABSTRACT FROM AUTHOR]