A highly diastereoselective five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates

A novel one-pot, five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates is described. A mixture of phenacyl bromide, malononitrile, isocyanide, and two equivalents of a dialkyl acetylenedicarboxylate undergoes a novel 1:1:1:2 addition reaction at ambient temperature in absolute ethanol to produce diastereoselectively the title compounds in good yields.     

A novel synthesis of 4,5-diaryl-6-arylamino-2,3-benzo-1,3a,6a-triazapentalenes

Treatment of N-alkyl- and N-aryl-imines of 2,3-diaryl- and 2-alkyl-3-aryl-3-(benzotriazol-1-yl)propenals with trifluoroacetic anhydride in THF at room temperature gave 5-alkyl-4-aryl-6-[N-alkyl (and aryl)-N-trifluoroacetyl]amino-2,3-benzo-1,3a,6a-triazapentalenes in moderate to good yields. On heating triazapentalenes having R²=aryl in MeOH at reflux, detrifluoroacetylation of triazapentalene occurred to give title compounds in good yields. However, the same treatment of triazapentalenes having R²=alkyl did not give the corresponding detrifluoroacetylation product. The title compounds and 5-alkyl-4-aryl-6-(N-alkyl-N-trifluoroacetyl)amino-2,3-benzo-1,3a,6a-triazapentalenes were found to be good precursors for the synthesis of 1-(o-aminophenyl)-3-arylamino-4-alkyl (and aryl)-5-arylpyrazoles and 1-(o-aminophenyl)-3-(N-alkyl-N-trifluoroacetyl)amino-4-alkyl (and aryl)-5-arylpyrazoles, respectively.     

Gold-Catalyzed Regiospecific Annulation of Unsymmetrically Substituted 1,5-Diynes for the Precise Synthesis of Bispentalenes

Precise control of the selectivity in organic synthesis is important to access the desired molecules. We demonstrate a regiospecific annulation of unsymmetrically substituted 1,2-di(arylethynyl)benzene derivatives for a geometry-controlled synthesis of linear bispentalenes, which is one of the promising structures for material science. A gold-catalyzed annulation of unsymmetrically substituted 1,2-di(arylethynyl)benzene could produce two isomeric pentalenes, but both electronic and steric effects on the aromatics at the terminal position of the alkyne prove to be crucial for the selectivity; especially a regiospecific annulation was achieved with sterically blocked substituents; namely, 2,4,6-trimetyl benzene or 2,4-dimethyl benzene. This approach enables the geometrically controlled synthesis of linear bispentalenes from 1,2,4,5-tetraethynylbenzene or 2,3,6,7-tetraethynylnaphthalene. Moreover, the annulation of a series of tetraynes with a different substitution pattern regioselectively provided the bispentalene scaffolds. A computational study revealed that this is the result of a kinetic control induced by the bulky NHC ligands.     

Formation of stereodefined multiply substituted all-cis octatetraenes, tricyclo[4.2.0.0]octa-3,7-dienes and pentalenes via CuCl- or FeCl3-mediated dimerization of 1-lithiobutadienes and 1,4-dilithiobutadienes

Dimerization of 1-lithiobutadienes and 1,4-dilithiobutadienes depended remarkably on the substituents and metal halide reagents. Stereodefined multiply-substituted linear all-cis octatetraenes were prepared in moderate yields via FeCl₃-mediated dimerization of 1-lithiobutadienes, while CuCl induced the dimerization of alkyl-substituted 1,4-dilithio-1,3-dienes to form linear all-cis octatetraenes and tricyclo[4.2.0.0^2,5]octa-3,7-dienes. Interestingly, stereodefined pentalene derivatives were also obtained when 1,4-dilithio-1,3-dienes possessed both phenyl and alkyl substituents.     

On the Gold‐Catalyzed Generation of Vinyl Cations from 1,5‐Diynes

Conjugated 1,5‐diynes bearing two aromatic units at the alkyne termini were converted in the presence of a gold catalyst. Under mild conditions, aryl‐substituted dibenzopentalenes were generated. Calculations predict that aurated vinyl cations are key intermediates of the reaction. A bidirectional approach provided selective access to the angular annulated product in high yield, which was explained by calculations.     

Diaceno[a,e]pentalenes: An Excellent Molecular Platform for High‐Performance Organic Semiconductors

Three diaceno[a,e]pentalene analogues with pendant sterically bulky di‐tert‐butylphenyl groups have been designed and synthesized. With the extension of the conjugated molecular framework, the molecular arrangement is apparently tuned by the balance between the π‐extended surface and pendant alkyl or aryl substituents. Theoretical calculations of the morphologies were in good agreement with the experimental results. Ambient‐stable field‐effect transistors based on dianthraceno[a,e]pentalene ( DAP ) have been fabricated, which exhibited excellent hole mobilities (up to 6.55 cm² V^?1 s^?1). Thus, this study has shown that diaceno[a,e]pentalenes are stable even with an extraordinarily large π‐surface area, and may thus serve as excellent molecular platforms for further exploring high‐performance semiconducting materials.