New enantiopure imidazolinium carbene ligands incorporating two hydroxy groups for Lewis acid-catalyzed diethyl zinc addition to aldehydes

New enantiopure imidazolinium carbene ligands incorporating two hydroxy functions have been synthesized from commercially available chiral amino alcohols and diamines. These ligands in combination with different metallic salts have been investigated in the diethylzinc addition to aldehydes with good yields and enantioselectivity.

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(−)-(R,R)-1,2-Diphenyl-N,N′-bis((R)-2-hydroxyethyl)-3-methyl) ethylenediamineC21H28N2O2Ee = 100%[α]D22=-30 (c 1.0, CHCl3)Source of chirality: chiral poolAbsolute configuration: (R,R)

(+)-(R,R)-1,2-Diphenyl-N,N′-bis(2-hydroxy-2-methylpropyl) ethylenediamineC21H32N2O2Ee = 100%[α]D22=+13 (c 0.5, MeOH)Source of chirality: chiral poolAbsolute configuration: (R,R)

(−)(-3-Bis-[(1S,2R)-2-hydroxy-1-methyl-2-phenyl-ethyl]-4,5-imidazolinium chlorideC21H27N2O2ClEe = 100%[α]D22=-16 (c 0.4, MeOH)Source of chirality: chiral poolAbsolute configuration: (1S,2R)

(−)-1,3-Bis-[(1S,2R)-2-hydroxy-1-methyl-2-phenyl-ethyl]-4,5-imidazolinium bromideC21H27N2O2BrEe = 100%[α]D22=-17 (c 1.0, MeOH)Source of chirality: chiral poolAbsolute configuration: (1S,2R)

(−)-3-Bis-[(1S,2R)-2-hydroxy-1-methyl-2-phenyl-ethyl]-4,5-imidazolinium iodideC21H27N2O2IEe = 100%[α]D22=-4 (c 0.3, MeOH)Source of chirality: chiral poolAbsolute configuration: (1S,2R)

(−)-1,3-Bis[(S)-1-(hydroxymethyl)-2-methylbenzyl]-4,5-imidazolinium tetrafluoroborateC21H27N2O2BF4Ee = 100%[α]D22=-71 (c 1.0, CHCl3)Source of chirality: chiral poolAbsolute configuration: (S)

(+)-1,3-Bis[(S)-1-(hydroxymethyl)-2-methylphenyl]-4,5-imidazolinium tetrafluoroborateC19H23N2O2BF4Ee = 100%[α]D22=+65 (c 0.65, MeOH)Source of chirality: chiral poolAbsolute configuration: (S)

(+)-(4R,5R)-Diphenyl-1,3-bis((R)-2-hydroxyethyl)-3-methyl)-4,5-dihydro-3H-imidazolinium tetrafluoroborateC21H27N2O2BF4Ee = 100%[α]D22=+51 (c 1.2, CHCl3)Source of chirality: chiral poolAbsolute configuration: (4R,5R)

(+)-(4R,5R)-Diphenyl-1,3-bis(2-hydroxy-2-methylpropyl)-4,5-dihydro-3H-imidazolinium tetrafluoroborateC23H31N2O2BF4Ee = 100%[α]D22=+150 (c 1.1, MeOH)Source of chirality: chiral poolAbsolute configuration: (4R,5R)