Redox-Divergent Hydrogen-Retentive or Hydrogen-Releasing Synthesis of 3,4-Dihydroisoquinolines or Isoquinolines

A rare Ru-catalyzed
highly selective synthesis of 3,4-dihydroisoquinolines
or isoquinolines is accomplished via a redox-divergent hydrogen-retentive
or hydrogen-releasing fashion. Notably, high cis-selectivity
of 3,4-dihydroisoquinolines is achieved. Potential applications are
shown by gram-scale reactions and very concise synthesis of N-containing
polycyclic aromatic compounds. Primary mechanistic investigations
indicate that the sequence of the major pathway involves Ru-catalyzed
C–H activation, alkyne insertion, and subsequent 6π-electrocyclization.