Synthesis of new alkoxy/sulfonate-substituted carbene precursors derived from [2.2]paracyclophane and their application in the asymmetric arylation of aldehydes

A series of novel planar chiral alkoxy/sulfonate-substituted carbene precursors have been designed and synthesized. They were used as N-heterocyclic carbene ligands in the Rh-catalyzed asymmetric addition of arylboronic acids to aromatic aldehydes, affording chiral diarylmethanols with high yields and moderate enantioselectivities.

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N,N′-Bis[(Sp)-(+)-12-methoxy-4-[2.2]paracyclophanyl]imidazolium triflateC38H37F3N2O5S[α]D20=+20.9 (c 0.36, CH2Cl2)Source of chirality: (Sp)-4-Amino-12-methoxy[2.2]paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(−)-12-isopropoxy-4-[2.2]paracyclophanyl]imidazolium triflateC42H45F3N2O5S[α]D20=-74.4 (c 0.68, CH2Cl2)Source of chirality: (Sp)-4-Amino-12-i-propoxy [2.2]paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(+)-12-trifluoromethanesulfonyloxy-4-[2.2]paracyclophanyl]imidazolium triflateC38H31F9N2O9S3[α]D20=+146.3 (c 0.36, CH2Cl2)Source of chirality: (Sp)-4-Amino-12-trifluoromethanesulfonyloxy[2.2]paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Rp)-(+)-12-methanesulfonyloxy-4-[2.2]paracyclophanyl]imidazolium bromideC37H37BrN2O6S2[α]D20=+82.6 (c 0.2, CH3CN)Source of chirality: (Rp)-4-Benzhydrylideneamino-12-hydroxy[2.2]paracyclophaneAbsolute configuration: (Rp)

N,N′-Bis[(Sp)-(+)-13-methoxy-4-[2.2]paracyclophanyl]imidazolium triflateC38H37F3N2O5S[α]D20=+81.7 (c 0.17, CH2Cl2)Source of chirality: (Sp)-4-Amino-13-methoxy[2.2]paracyclophaneAbsolute configuration: (Sp)

N,N′-Bis[(Sp)-(-)-12-methoxy-4-[2.2]paracyclophanyl]imidazolinium tetrafluoroborateC37H39BF4N2O2[α]D20=-58.8 (c 0.4, CH2Cl2)Source of chirality: (Sp)-4-Amino-12-methoxy[2.2]paracyclophaneAbsolute configuration: (Sp)