New cyclic aminals derived from rac-trans-1,2-diaminocyclohexane: synthesis and crystal structure of racemic 1,8,10,12-tetraazatetracyclo[8.3.1.1.8,1202,7] pentadecane and a route to its enantiomerically pure (R,R) and (S,S) isomers

New enantiomerically pure macrocyclic aminals (2 R ,7 R )- and (2 S ,7 S )-1,8,10,12-tetraazatetracyclo[8.3.1.1. 8,12 0 2,7 ]pentadecane ( 4a and 4b ) were obtained by a three component reaction between their respective pure enantiomer of trans -1,2-diaminocyclohexane, ammonia, and formaldehyde. Additionally, the X-ray structure of the racemic compound 4 and the specific rotations of the racemic and optically pure compounds were determined. To further understand the synthetic utilities of enantiomers 4a and 4b, Mannich-type reactions with 1 H -benzotriazole were performed, affording (3a R ,7a R )- and (3a S ,7a S )-1,1′-{[2,3,3a,4,5,6,7,7a-octahydro-1 H -1,3-benzimidazole-1,3-diyl]bis(methylene)}bis-1 H -benzotriazole ( 9 and 10 ) and allowing for new possibilities related to the preparation of chiral ligands for asymmetric catalysis.