The evaluation of a range of enantiomerically pure NHCs, prepared in situ from imidazolinium or triazolium salt precatalysts, to promote the catalytic enantioselective Steglich rearrangement of oxazolyl carbonates to their C-carboxyazlactones, is reported. Modest levels of enantioselectivity (up to 66% ee) are observed using oxazolidinone derived NHCs.
N1,N2-Bis((S)-1-phenylethyl)imidazolinium tetrafluoroborateC19H23BF4N2Ee 100%
[α]D20=+7.8 (c 0.5, CHCl3)Souce of chirality: (S)-α-methylbenzylamineAbsolute configuration: (S,S)
N1,N2-Bis((S)-1-phenylethyl)imidazolium tetrafluoroborateC11H21BF4N2Ee 100%
[α]D20=+7.8 (c 0.5, CHCl3)Source of chirality: (S)-α-methylbenzylamineAbsolute configuration: (S,S)
(S)-1-Benzyl-3-(2-tert-butylphenyl)-5-isopropyl-4,5-dihydro-1H-imidazolium tetrafluoroborateC23H31BF4N2Ee 100%
[α]D20=-0.7 (c 1.4, CHCl3)Source of chirality: l-valineAbsolute configuration: (S)
(3S,7S)-3,7-Diisopropyl-2,3,7,8-tetrahydroimidazo[4,3-b:5,1-b′]bis(oxazole)-4-ium trifluoromethanesulfonateC14H21F3N2O5SEe 100%
[α]D20=+54.6 (c 0.5, CH2Cl2)Source of chirality: l-valineAbsolute configuration: (S,S)
(5aR,10bS)-2-Phenyl-4,5a,6,10b-tetrahydroindeno[2,1-b][1,2,4]triazolo[4,3-d][1,4]-oxazinium tetrafluoroborateC18H16BF4N3OEe 100%
[α]D20=+300.4 (c 0.5, MeCN)Source of chirality: (1S,2R)-1-amino-2,3-dihydro-1H-inden-2-olAbsolute configuration: (5aR,10bS)
(5aS,6R,9S,9aR)-6,11,11-Trimethyl-2-phenyl-5a,6,7,8,9,9a-hexahydro-4H-6,9-methano-benzo[b][1,2,4]triazolo[4,3-d][1,4]oxazin-2-ium tetrafluoroborateC19H24BF4N3OEe 100%
[α]D20=+28.8 (c 0.5, CHCl3)Source of chirality: D-camphorAbsolute configuration: (5aS,6R,9S,9aR)
(S)-5-Benzyl-2-phenyl-6,8-dihydro-5H-[1,2,4]triazolo[3,4-c][1,4]oxazin-2-ium tetrafluoroborateC18H18BF4N3OEe 100%
[α]D20=-18.1 (c 0.8, MeOH)Source of chirality: l-phenylalanineAbsolute configuration: (S)
(S)-5-Benzyl-2,6,6-triphenyl-6,8-dihydro-5H-[1,2,4]triazolo[3,4-c][1,4]oxazin-2-ium tetrafluoroborateC30H26BF4N3OEe 100%
[α]D20=+3.0 (c 0.5, MeOH)Source of chirality: l-valineAbsolute configuration: (S)
(R)-5-Benzyl-2-phenyl-6,7-dihydro-5H-pyrrolo[2,1-c][1,2,4]triazol-2-ium tetrafluoroborateC18H18BF4N3Ee 100%
[α]D20=+8.7 (c 1.04, MeCN),Source of chirality: l-phenylalanineAbsolute configuration: (S)
(S)-5-((tert-Butyldimethylsilyloxy)diphenylmethyl)-2-phenyl-2,5,6,7-tetrahydropyrrolo[2,1-c][1,2,4]triazolium tetrafluoroborateC30H36BF4N3SiOEe 100%
[α]D20=-108.4 (c 0.5, MeCN),Source of chirality: l-pyroglutamic acidAbsolute configuration: (S)
(S)-6,6-Dimethyl-2-phenyl-5-isopropyl-5,6-dihydrooxazolo[2,3-c][1,2,4]triazol-2-ium tetrafluoroborateC15H20BF4N3OEe 100%
[α]D20=-5.0 (c 1.0, MeCN)Source of chirality: l-valineAbsolute configuration: (S)
(S)-5-Benzyl-6,6-dimethyl-2-phenyl-5,6-dihydrooxazolo[2,3-c][1,2,4]triazol-2-ium tetrafluoroborateC19H20BF4N3OEe 100%
[α]D20=-73.0 (c 0.5, MeCN)Source of chirality: l-phenylalanineAbsolute configuration: (S)