Facile Optical Resolution of a Dibenzopyrazinoazepine Derivative and the Nature of Molecular Recognition of Amines by Chiral 2,3-Di-O-(arylcarbonyl)tartaric Acids

A facile optical resolution of recemic 1,2,3,4,10,14b-hexahydrodibenzo[c,f]pyrazino[1,2-a]azepine (1) was developed using 2,3-di-O-benzoyl-d-(−)-tartaric acid ((+)-DBT) as a resolving agent. The resolution efficiency depends remarkably on the (+)-DBT : 1 ratio. When (+)-DBT and recemic 1 were mixed in methanol–water (9 : 1 v/v) in a 1 : 4 stoichiometry, a crystalline salt consisting of (+)-DBT, (R)-1, methanol, and water in a 1 : 2 : 2 : 2 ratio crystallized preferentially in a fair yield. X-Ray crystallographic analysis showed its highly ordered supramolecular structure: (+)-DBT molecules self-assemble via hydrogen bonding with the aid of water and methanol to form a puckered layer, and stacking of (R)-1 molecules constructs a column which is sandwiched in between the puckered layers. The X-ray crystallographic data reported for the salts that consist of amines and DBT were reinvestigated to reveal that most of the host frameworks derived from DBT have a layer structure similar to the above puckered one.