Optical resolution of trans-bicyclo[2.2.1]heptane-2,3-diamine: chiral recognition in the crystal of its complex with (2R,3R)-O,O′-dibenzoyltartaric acid

Abstract

The synthesis of trans-bicyclo[2.2.1]heptane-2,3-diamine (6c), its optical resolution via formation of its complex with (2R,3R)-O,O′-dibenzoyltartaric acid (–BTA), and the crystal structure determination of this complex by X-ray diffraction techniques are reported. The absolute configuration of 6c in the complex has been determined to be (S,S)-6c from the endowed chirality of –BTA, thus optical resolution of 6c is achieved. Crystal data for the (S,S)-6c·-(–BTA) complex is reported: C₂₅H₂₈N₂O₈·2H₂O, M= 520.54, monoclinic P2₁, a= 9.150(1), b= 8.581(1), c= 17.036(1)Å, β= 103.30(1)°, V= 1301 (2)ų, Z= 2, R= 0.037. The crystal of the molecular complex is found to have a multilamellar structure partitioned by thin hydrogen bonded sheets containing complex ammonium–carboxylate–water hydrogen bonds. Attached on both sides of the sheet, monolayer templates with benzoyl groups of –BTA and bicycloheptane fragments of 6c stack with the next templates to form hydrophobic bilayers. In the monolayer template, a cavity is formed surrounded by two pairs of two benzoyl groups distinguished from each other by their orientations toward the hydrogen bond sheet. The cavity provides a final site for the chiral recognition of 6c. The (S,S)-enantiomer of 6c is probably distinguished from the (R,R)-enantiomer by the favourable orientation of bicycloheptane skeleton in the cavity.