Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed...

We report the concise synthesis and chir-(optical) properties of an azaborathia[9]helicene consisting of two thienoazaborole motifs. The key intermediate, a highly congested teraryl with nearly parallel isoquinoline moieties, was generated as a mixture of atropisomers upon fusion of the central thiophene ring of the dithienothiophene moiety. These diastereomers were characterized by single crystal X-ray analysis revealing intriguing interactions in the solid state. Subsequent insertion of boron into the aromatic scaffold via silicon-boron exchange involving triisopropylsilyl groups fixed the helical geometry, thereby establishing a novel method for the preparation of azaboroles. The ligand exchange at boron in the final step afforded the blue emitter displaying a fluorescence quantum yield of 0.17 in CH 2 Cl 2 and excellent configurational stability. Detailed structural and theoretical investigation of unusual atropisomers and the helicene provide insights into their isomerization processes.

We report the enantioselective synthesis of azaborole helicenes from enantioenriched axially chiral precursors. The borylation/metal exchange reaction sequence affords target compounds with full transfer of chirality from the corresponding biaryls. Experimental studies provide insights into the configurational stability of the heteroobiaryls and (chiro)ptical properties. The structure of the phenyl-substituted helicene was unambiguously confirmed by single crystal X-ray analysis.

We report the concise synthesis and chir-(optical) properties of an azaborathia[9]helicene consisting of two thienoazaborole motifs. The key intermediate, a highly congested teraryl with nearly parallel isoquinoline moieties, was generated as a mixture of atropisomers upon fusion of the central thiophene ring of the dithienothiophene moiety. These diastereomers were characterized by single crystal X-ray analysis revealing intriguing interactions in the solid state. Subsequent insertion of boron into the aromatic scaffold via silicon-boron exchange involving triisopropylsilyl groups fixed the helical geometry, thereby establishing a novel method for the preparation of azaboroles. The ligand exchange at boron in the final step afforded the blue emitter displaying a fluorescence quantum yield of 0.17 in CH 2 Cl 2 and excellent configurational stability. Detailed structural and theoretical investigation of unusual atropisomers and the helicene provide insights into their isomerization processes.

Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed that provides access to azaborine containing helicenes (BN-helicenes). This borylation process proceeds via protonation of an aminoborane with bistriflimidic acid. DFT calculations reveal the borenium cation formed by protonation to be more electrophilic than the product derived from aminoborane activation with BBr3. The synthesised helicenes include BN-analogues of archetypal all carbon [5]- and [6]helicenes. The replacement of a CC with a BN unit (that has a longer bond) on the outer helix increases the strain in the BN congeners and the racemization half-life for a BN-[5]helicene relative to the all carbon [5]helicene. BN incorporation also increases the fluorescence efficency of the helicenes, a direct effect of BN incorporation altering the distribution of the key frontier orbitals across the helical backbone relative to carbo-helicenes.