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We report the synthesis and structural elucidation of two series of chiral cyclic squaramides, i.e. six- and twelve-membered ring squaramides 4 and 6, based on the cyclobutenedione structure, containing enantiomerically pure (1R,2R)-1,2-diphenylethylenediamine as the chiral element. Compounds 4a-d obtained from alkylation of 3, crystallize in space groups of monoclinic P21, monoclinic P21, monoclinic chiral P212121, and the orthorhombic C2221, respectively. For the first time the crystal structures of six-membered ring chiral cyclic squaramides are reported. These novel ligands have been tested in the enantioselective addition of diethylzinc to aryl aldehydes to give the corresponding alcohols in moderate yields, albeit with low enantioselectivity.

Synthesis and structural features of chiral cyclic squaramides and their application in asymmetric catalytic reaction