Diazadioxadecalin and salen podands and macrocycles within dynamic combinatorial virtual libraries: Structure, prototropy, complexation and enantioselective catalysis

The reactions of L-1,4-diaminobutanediol (3) and D-2,3-diaminobutanediol (4) with salicyl aldehyde provide the tautomeric manifolds of L-1,4-bis(salicylideneamino)-2,3-butanediol (5) and D-2,3-bis(salicylideneamino)-1,4-butanediol (6), respectively. O-alkylation of the salicyl moiety stabilizes the closed dioxadiazadecalin (DODAD) and diazadioxadecalin (DADOD) isomers (7″, 8″) and accordingly, the dialdehyde 1,2-bis(o-formylphenoxy)-ethane (9) led to the respective macrocyclic manifolds (10-10″ and 11-11″). These tautomeric manifolds are typical target-driven dynamic combinatorial virtual libraries, which can be biased by complex formation with metal ions of different ionic radius. A rare instance of simultaneous occurrence of keto-enamine and phenol-imine tautomers in the solid state of 6 was unravelled (X-ray at two temperatures) and the strength of the intramolecular hydrogen bonding (and hence, the extent of ring closure) in 6 is temperature dependent. Compounds 6, 11 and 12-14 constitute a new class of salens, which form heavy and transition metal complexes. Some such Mn(III) complexes are good chirality inducing catalysts, as found in asymmetric indene epoxidation reactions.