Assembly of chiral monodentate ligands to chelates by donor–acceptor interactions

The first examples of assembling monodentate oxazoline donor and acceptor ligands by charge transfer interactions are described to mimic bidentate ligands in asymmetric catalysis. The corresponding copper(II) complexes were used in an enantioselective Diels–Alder reaction and showed very high efficiency, but only moderate stereoselectivity. These complexes were successfully recovered and reused after precipitation in pentane.

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(Anthracen-10-yl)methyl 3-((S)-4,5-dihydro-4-isopropyloxazol-2-yl)propanoateC24H25NO3[α]43625=-56 (c 0.5, CHCl3)Absolute configuration (S) (assigned from (S)-valinol)

3-((S)-4,5-Dihydro-4-isopropyloxazol-2-yl)propyl 2,5,7-trinitro-9-oxo-9H-fluorene-4-carboxylateC23H20N4O10[α]43625=-102 (c 0.3, CHCl3)Absolute configuration (S) (assigned from (S)-valinol)

(Anthracen-10-yl)methyl 3-((R)-4,5-dihydro-4-phenyloxazol-2-yl)propanoateC27H23NO3[α]43625=+24 (c 0.6, CHCl3)Absolute configuration (R) (assigned from (R)-phenylglycinol)

3-((R)-4,5-Dihydro-4-phenyloxazol-2-yl)propyl 2,5,7-trinitro-9-oxo-9H-fluorene-4-carboxylateC26H18N4O10[α]58925=+33 (c 0.4, CHCl3)Absolute configuration (R) (assigned from (R)-phenylglycinol)

(Anthracen-10-yl)methyl 3-((S)-4-tert-butyl-4,5-dihydrooxazol-2-yl)propanoateC25H27NO3[α]43625=-6 (c 0.4, CHCl3)Absolute configuration (S) (assigned from (S)-tert-leucinol)

3-((S)-4-tert-Butyl-4,5-dihydrooxazol-2-yl)propyl 2,5,7-trinitro-9-oxo-9H-fluorene-4-carboxylateC24H22N4O10[α]43625=-74 (c 0.5, CHCl3)Absolute configuration (S) (assigned from (S)-tert-leucinol)