Synthesis of planar chiral imidazo[1,5-a]pyridinium salts based on [2.2]paracyclophane for asymmetric β-borylation of enones

Novel planar chiral pseudo-geminal and pseudo-ortho-oxazoline substituted [2.2]paracyclophanyl imidazo[1,5-a]pyridinium triflates were synthesized. During the synthesis of a pseudo-ortho imidazo[1,5-a]pyridinium triflate based on [2.2]paracyclophane, the diastereoisomers of 4-amino-12-oxazolinyl[2.2]paracyclophane were separated. The imidazo[1,5-a]pyridinium triflates were used as carbene precursors in Cu-catalyzed enantioselective conjugate β-borylation of enones. In preliminary tests of a series of ligands and substrates, we obtained up to 84% enantioselectivity.

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(R,4Rp,13Sp)-3-{13-(4-Phenyloxazolin-2-yl)[2.2]paracyclophane-4-yl}imidazo[1,5-a]pyridinium triflateC33H27F3N3O4S[α]D20=+43.9 (c 0.2, CH2Cl2)Source of chirality: (R,4Rp,13Sp)-4-bromo-13-(4-phenyloxazolin-2-yl)[2.2]paracyclophaneAbsolute configuration: (R,4Rp,13Sp)

(R,4Sp,13Rp)-3-{13-(4-Phenyloxazolin-2-yl)[2.2]paracyclophane-4-yl}imidazo[1,5-a]pyridinium triflateC33H27F3N3O4S[α]D20=+16.7 (c 0.3, CH2Cl2)Source of chirality: (R,4Sp,13Rp)-4-bromo-13-(4-phenyloxazolin-2-yl)[2.2]paracyclophaneAbsolute configuration: (R,4Sp,13Rp)

(R,Rp)-3-{12-(4-Phenyloxazolin-2-yl)[2.2]paracyclophane-4-yl}imidazo[1,5-a]pyridinium triflateC33H27F3N3O4S[α]D20=+187.5 (c 0.2, CH2Cl2)Source of chirality: (R,Rp)-4-benzhydrylideneamino-12-(4-phenyl oxazolin-2-yl)[2.2]paracyclophaneAbsolute configuration: (R,Rp)

(R,Sp)-3-{12-(4-Phenyloxazolin-2-yl)[2.2]paracyclophane-4-yl}imidazo[1,5-a]pyridinium triflateC33H27F3N3O4S[α]D20=-122.4 (c 0.2, CH2Cl2)Source of chirality: (R,Sp)-4-benzhydrylideneamino-12-(4-phenyl oxazolin-2-yl)[2.2]paracyclophaneAbsolute configuration: (R,Sp)

(S,Sp)-3-{12-(4-t-Butyloxazolin-2-yl)[2.2]paracyclophane-4-yl}imidazo[1,5-a]pyridinium triflateC31H31F3N3O4S[α]D20=-235.7 (c 0.2, CH2Cl2)Source of chirality: (S,Sp)-4-bromo-12-(4-t-butyloxazolin-2-yl)[2.2]paracyclophaneAbsolute configuration: (S,Sp)