Novel C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands: synthesis and application in asymmetric diethylzinc addition to aldehydes

First synthesis of C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands is described. The Mukaiyama–Michael reaction was applied as an important reaction for the synthesis of 2,2-bipyridylpropane 9. Among the ligands synthesized, ligand 11 exhibits excellent chiral induction (up to 97% ee) in diethylzinc addition to various aldehydes. The use of additional Lewis acid such as Ti(OiPr)4 in diethylzinc addition reaction is not required for the present catalytic system.

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2,2′-(Propane-2,2-diyl)bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinoline)C27H34N2Ee ⩾97%[α]D20.7=+79.3 (c 1.00, CHCl3)Source of chirality: (1R)-(+)-α-pineneAbsolute configuration: (5S,5′S,7S,7′S)

2,2′-(Propane-2,2-diyl)bis(6,6-dimethyl-8-(1-hydroxy-1-methylethyl)5,6,7,8-tetrahydro-5,7-methanoquinoline)C33H46N2O2Ee ⩾ 97%[α]D20.0=-1.0 (c 4.20, CHCl3)Source of chirality: (1R)-(+)-α-pineneAbsolute configuration: (5S,5′S,7S,7′S,8R,8′R)

2,2′-(Propane-2,2-diyl)bis(6,6-dimethyl-8-(1-hydroxy-1-phenylethyl)-5,6,7,8-tetrahydro-5,7-methanoquinoline)C53H54N2O2Ee ⩾ 97%[α]D22.1=-303.2 (c 1.00, CHCl3)Source of chirality: (1R)-(+)-α-pineneAbsolute configuration: (5S,5′S,7S,7′S,8R,8′R)