Synthesis And Study Of C3-Asymmetric Heterocycle-Fused Benzo-Phenanthrene Derivatives

In recent years numerous attention has been paid to the synthesis and application of heterocycle-fused polycyclic aromatics due to their potenial application in organic semiconductor devices such as organic field effect transistors,organic photovoltaic batteries and other applications.The heterocycle-fused polycyclic aromatics have the advantages of high field mobility,high current switching ratio and good solubility.Due to good photoelectric properties of polycyclic(hetero)aromatics,we designed and completed a series of fused heterocycles with a central benzo-phenanthrene core and N/O/S atoms.They are characterized by both Benzophenanthrene as the parent nucleus and are both C3-asymmetric structures.The first part is focused on the study of C3-asymmetric heteroacyles with benzophenanthrene and thiophene or furan motifs.The key intermediates,2,6,11-trihalo-3,7,10-trimethoxy-benzophenanthrene were obtained by the cyclotrimerization of 2-haloanisole in the presence of catalytic conc.H2SO4 and anhydrous FeCl3 as oxidant.As for trifuran-fused benzophenanthrenes,2,6,11-tribromo-3,7,10-trimethoxy-benzophenanthrene was employed as starting materials,the demethylations were completed with BBr3,followed by the reaction of Ac2O to furnish the protection of hydroxyl groups,then palladium-catalyzed Sogonashira reaction with various acetylenes,followed with Cs2CO3-mediated ring-closure to afford the target molecules efficiently.On the other hand,2,6,11-trichloro-3,7,10-trimethoxy-benzophenanthrene was used to construct trithiophene-fused benzophenanthrene.The trihalo precursor was demethylated with BBrn,followed with the reaction of Tf2O to obtain triflates,which were perfomed with various acetylenes by palladium-catalyzed Sonogashira reactions.The ring closures were completed with Na2S·9H2O to afford trithiophene-fused-benzophenanthrenes.The second part is focused on iso-tricarbazoles/iso-tri(dibenzofuran)/iso-tri(dibenzothiophene)by use of the 2,6,11-tribromo-3,7,10-trimethoxybenzene as raw materials.(1)Palladium-catalyzed Suzuki coupling between o-methoxy phenyl-boronic acid and 2,6,11-tribromo-3,7,10-trimethoxy-benzophenanthrene and was carried out with Pd132 as catalysts to obtain intermediate with six methoxy groups,which was demethylated with BBr3 and and subsequently sulfonated with Tf2O,followed by a double palladium-catalyzed Buchwald-Hartiwig C-N reaction to form trimeric carbazoles.(2)Pd132-catalyzed Suzuki coupling o-chlorophenyl boronic acid with 2,6,11-tribromo-3,7,10-trimethoxy-benzophenanthrene was carried out,followed by demethylation with BBr3 and subsequent ring closure to obtain the trimeric dibenofurans.An alternative route is also hired with 2,6,11-tribromo-3,7,10-trimethoxy-benzophenanthrene through demethylation with BBr3,followed by etherification with o-fluorobenzonitrile in the presence of Cs2CO3,and finally C-H activation with Pd(OAc)2/K2CO3 to form cyano-substituted iso-tri(dibenzofuran)derivatives.(3)The coupling of 2,6,11-tribromo-3,7,10-trimethoxybenzene and o-fluorobenzene boronic acid with Pd132,followed by demethylation and sulfonation with Tf2O.Subsequent reaction with ethyl mercaptopropionate and the final step was conducted with t-BuOK ring to get iso-tri(dibenzothiophene).