Complete reversal of enantioselection using oxazoline-containing Schiff base ligands derived from l-serine in enantioselective addition of diketene to aldehydes

Starting from one stereogenic center (in this case from l-serine), we obtained two chiral Schiff bases possessing oxazoline moieties, each of which recognized a different enantioface of aldehydes with a high enantiomeric excess [up to 93% ee (R) and 89% ee (S)] in the addition reaction of diketene to 2-furfural.

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(4S)-4-[(1-Hydroxyl-1-methyl)-ethyl]-2-[(2-hydroxyl-3,5-di-tert-butyl)-phenyl]-4,5-dihydro-1,3-oxazolineC20H31NO3[α]D27=+3.3 (c 1.0, CHCl3)Source of chirality: l-serine

(4S)-4-Hydroxymethyl-5,5-dimethyl-2-[(2-hydroxyl-3,5-di-tert-butyl)-phenyl]-4,5-dihydro-1,3-oxazolineC20H31NO3[α]D27=-30.8 (c 1.0, CHCl3)Source of chirality: l-serine

(4S)-4-[(1-Ethyl-1-hydroxyl-propyl)-2-[(2-hydroxyl-3,5-di-tert-butyl)-phenyl]-4,5-dihydro-1,3-oxazolineC22H35NO3[α]D27=-1.2 (c 1.0, CHCl3)Source of chirality: l-serine

(4S)-4-Hydroxymethyl-5,5-diethyl-2-[(2-hydroxyl-3,5-di-tert-butyl)-phenyl]-4,5-dihydro-1,3-oxazolineC22H35NO3[α]D27=-24.5 (c 1.0, CHCl3)Source of chirality: l-serine

(4S)-4-(Hydroxyl-diphenyl)-methyl]-2-[(2-hydroxyl-3,5-di-tert-butyl)-phenyl]-4,5-dihydro-1,3-oxazolineC30H35NO3[α]D27=-41.2 (c 1.0, CHCl3)Source of chirality: l-serine

(4S)-4-Hydroxymethyl-5,5-diphenyl-2-[(2-hydroxyl-3,5-di-tert-butyl)-phenyl]-4,5-dihydro-1,3-oxazolineC30H35NO3[α]D27=-232.5 (c 1.0, CHCl3)Source of chirality: l-serine