Highly sterically hindered binaphthalene-based monophosphane ligands: synthesis and application in stereoselective Suzuki–Miyaura reactions

A series of new sterically hindered (R)-(2′-aryl-1,1′-binaphthalene-2-yl)phosphanes with ortho-substituted phenyls as aryl groups were prepared via Negishi monoarylation of enantiopure 2,2′-dibromo-1,1′-binaphthalene followed by lithiation and quenching with diphenylphosphanyl or dicyclohexylphosphanyl chloride. These ligands were applied to the stereoselective Suzuki–Miyaura coupling for the preparation of substituted biaryls. The enantioselectivity correlated positively when increasing the hindrance of the 2′-aryl group of the ligand. Using the best performing diphenylphosphane ligand with a 2,6-dimethoxyphenyl aryl group, various arylnaphthalenes were prepared in high to excellent yields (68–99%) with low to good ee (12–75% ee), the latter being comparable to the best values reported when using other chiral monophosphane ligands.

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(R)-[2′-(2-Methoxyphenyl)-1,1′-binaphthalene-2-yl]diphenylphosphaneC39H29OP[α]D20=+14.3 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)

(R)-[2′-(2-Methylphenyl)-1,1′-binaphthalene-2-yl]diphenylphosphaneC39H29P[α]D20=+21.65 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)

(R)-[2′-(2,6-Dimethoxyphenyl)-1,1′-binaphthalene-2-yl]diphenylphosphaneC40H31O2P[α]D20=+10.15 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)

(R)-[2′-(3,5-Dimethoxyphenyl)-1,1′-binaphthalene-2-yl]diphenylphosphaneC40H31O2P[α]D20=+16.9 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)

(R)-Dicyclohexyl[2′-(2-methoxyphenyl)-1,1′-binaphthalene-2-yl]phosphane–boraneC39H44BOP[α]D20=+14.0 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)

(R)-Dicyclohexyl[2′-(2-methylphenyl)-1,1′-binaphthalene-2-yl]phosphane–boraneC39H44BP[α]D20=+8.2 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)

(R)-Dicyclohexyl[2′-(2,6-dimethoxyphenyl)-1,1′-binaphthalene-2-yl]phosphane–boraneC40H46BO2P[α]D20=+17.75 (c 1, CHCl3)Source of chirality: (R)-2,2′-Dibromo-1,1′-binaphthaleneAbsolute configuration: (R)