The synthesis of tetradentate salens derived from (3R,4R)-N-substituted-3,4-diaminopyrrolidines and their application in the enantioselective trimethylsilylcyanation of aromatic aldehydes

The in situ formed Ti(IV) complexes of pyrrolidine-based chiral salen ligands derived from natural l-tartaric acid were evaluated as catalysts in the enantioselective trimethylsilylcyanation of aromatic aldehydes. The different activity and selectivity of the catalysts in the formation of the products were found to be dependent on the N-substituent of the pyrrolidine.

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(3R,4R)-N′,N″-Bis[2′-hydroxynaphthylidene]-N-phenyl-3,4-diaminopyrrolidineC32H27N3O2[α]D25=-620 (c 1.0, CH2Cl2)Chirality source: l-tartaric acidAbsolute configuration: (3R,4R)

(3R,4R)-N′,N″-Bis[2′-hydroxynaphthylidene]-N-cyclohexyl-3,4-diaminopyrrolidineC32H33N3O2[α]D25=-305 (c 1.0, CH2Cl2)Chirality source: l-tartaric acidAbsolute configuration: (3R,4R)

(3R,4R)-N′,N″-Bis[3′,5′-di-t-butylsalicylidene]-N-cyclohexyl-3,4-diaminopyrrolidineC40H61N3O2[α]D25=-320 (c 1.0, CH2Cl2)Chirality source: l-tartaric acidAbsolute configuration: (3R,4R)

(3R,4R)-N′,N″-Bis[3′,5′-di-t-butylsalicylidene]-N-phenyl-3,4-diaminopyrrolidineC40H55N3O2[α]D25=-350 (c 1.0, CH2Cl2)Chirality source: l-tartaric acidAbsolute configuration: (3R,4R)