首页|Inherently Chiral 6,7-Diphenyldibenzo[e,g][1,4]diazocine:Enantioselective Synthesis and Application as a Ligand Platform
Inherently Chiral 6,7-Diphenyldibenzo[e,g][1,4]diazocine:Enantioselective Synthesis and Application as a Ligand Platform
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Inherently chiral 6,7-diphenyldibenzo[e,g][1,4]diazo-cine(DDD)has been synthesized enantioselectively for the first time via chiral phosphoric acid(CPA)-catalyzed cyclocondensation of readily available[1,1'-biphenyl]-2,2'-diamine(1a)and benzil(2a)in 82％yield,with 98％ee under mild reaction conditions.The strategy could also be applied to racemic biaryl dia-mines through kinetic resolution.The unexpectedly high interconversion energy barriers between the enantiomers(ΔG=39.5 kcal/mol)and the chemical stability rendered DDD an ideal platform for develop-ing new chiral ligands and catalysts.Unique inherently chiral DDD-based phosphoramidites,phosphoric acid,mono-and diphosphine ligands were prepared from optically pure diphenol derivative DDDOL as a common precursor.Preliminary asymmetric reactions catalyzed by Pd or Rh in the presence of newly devel-oped ligands exhibited comparable or even better enantioselectivities than the corresponding BINOL-or SPINOL-derived ligands.Density functional theory calculation revealed the origin of the enantioselectiv-ity during the process.
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