Planar chiral imidazolium salts based on [2.2]paracyclophane in the asymmetric rhodium-catalyzed 1,2-addition of arylboronic acids to aldehydes

A series of planar chiral imidazolium salts derived from [2.2]paracyclophane have been synthesized and characterized. By using these imidazolium salts as carbene precursors, the Rh-catalyzed 1,2-addition of arylboronic acids to aldehydes proceeded readily with low catalyst loadings (0.03–0.3 mol %) and gave a variety of chiral diarylmethanols in excellent yields and moderate enantioselectivities.

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N,N′-Bis[(Sp)-(+)-12-bromo-4-[2.2]paracyclophanyl]imidazolium chlorideC35H31Br2ClN2[α]D20=+26.7 (c 0.50, CHCl3)Source of chirality: (Sp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Sp)

N,N′-bis[(Sp)-(+)-12-bromo-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC36H31Br2F3N2O3S[α]D20=+18 (c 1.3, CHCl3)Source of chirality: (Sp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(+)-12-(2-methoxyphenyl)-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC50H44F3N2O5S[α]D20=+83.2 (c 0.50, CHCl3)Source of chirality: (Sp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(+)-12-phenyl-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC48H40F3N2O3S[α]D20=+64.7 (c 0.50, CHCl3)Source of chirality: (Sp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(+)-12-(3-methoxyphenyl)-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC50H44F3N2O5S[α]D20=+78.5 (c 0.50, CHCl3)Source of chirality: (Sp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(+)-12-(1-Naphthyl)-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC56H44F3N2O3S[α]D20=+121.3 (c 0.50, CHCl3)Source of chirality: (Sp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[((4Rp,13Sp)-13-bromo-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC36H31Br2F3N2O3S[α]D20=+151.0 (c 0.50, CHCl3)Source of chirality: (4Rp,13Sp)-4-amino-13-bromo[2.2]paracyclophaneAbsolute configuration: (4Rp,13Sp)

N,N′-Bis[(4Rp,13Sp)-13-phenyl-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC48H40F3N2O3S[α]D20=+172.8 (c 0.50, CHCl3)Source of chirality: (4Rp,13Sp)-4-amino-13-bromo[2.2]paracyclophaneAbsolute configuration: (4Rp,13Sp)

N,N′-Bis[(4Rp,13Sp)-13-(3-methoxyphenyl)-4-[2.2]paracyclophanyl]imidazolium trifluoromethanesulfonateC50H44F3N2O5S[α]D20=+210.3 (c 0.50, CHCl3)Source of chirality: (4Rp,13Sp)-4-amino-13-bromo[2.2]paracyclophaneAbsolute configuration: (4Rp,13Sp)

N,N′-Bis[(Rp)-(−)-4-[2.2]paracyclophanyl]imidazoliumTrifluoromethanesulfonateC36H33F3N2O3S[α]D20=-26.4 (c 0.50, CHCl3)Source of chirality: (4Rp,13Sp)-4-amino-13-bromo[2.2]paracyclophaneAbsolute configuration: (Rp)

N,N′-Bis[(Rp)-(−)-12-bromo-4-[2.2]paracyclophanyl]imidazolinium TetrafluoroborateC35H33BBr2F4N2[α]D20=-52.0 (c 0.12, CHCl3)Source of chirality: (Rp)-4-amino-12-bromo[2.2] paracyclophaneAbsolute configuration: (Rp)