1,8,13‐Trialkyl(aryl)silyl‐9‐hydroxytriptycenes (trisilyltriptycenes) were synthesized by the triple addition of ynolates and 3‐silylbenzynes with high regioselectivity. Benzene rings in the resulting triptycenes were highly distorted where the dihedral angles between the substituents were as high as 35°. The distortion energy induced step‐by‐step halogenation reactions to yield halogenated triptycenes, including chiral triptycenes. The 1,8,13‐trihalogenated triptycenes were then converted to 1,8,13‐functionalized triptycenes.
We developed the novel one-pot synthetic method of substituted triptycenes by the reaction of ynolates and arynes. This four-step process involves three cycloadditions and electrocyclic ring opening of the strained Dewar anthracene. Each of the three related but structurally distinct classes of nucleophiles (ynolate,enolate,and anthracenolate) reacts with o-benzyne in the same predictable manner controlled by chelation and negative hyperconjugation. The resulting functionalized C 3-symmetrical triptycenes hold promise in the design of functional materials.
The thermal expansion coefficients of glass fiber–polymer composites were calculated applying the solid cylindrical model taking into account the interaction effects among the glass fibers. The stress and displacement in the composite model were determined as functions of the thermal stress. It was found theoretically that the deviation of the thermal expansion coefficient from the linear mixture relationship based on volume additivity appeared at around Tg + 20 K upon cooling. The thermal expansion coefficient of the composite was also found to be markedly dependent on the dispersion state of the glass fibers. An expression for the difference in the Tg of the matrix resin in the composite from that in the unloaded resin was obtained on the assumption that the volume change of the matrix resin caused by mixing was compensated by free volume expansion. The experimental results obtained by differential scanning calorimetry (DSC) measurements were found to agree well with the theoretically predicted ones.
A Pd‐catalyzed domino reaction of 1,8,13‐tribromo‐9‐methoxytriptycenes is reported. Under conventional Suzuki coupling conditions, the triptycenes underwent multiple transformations to give 1,9‐bridged triptycenes. Based on mechanistic investigations, a single Pd catalyst functions as Pd0, PdII and PdIV species to catalyze four distinct processes: (1) aryl to alkyl 1,5‐Pd migration, (2) intramolecular arylation, (3) homocoupling of phenylboronic acid and (4) Suzuki coupling. DFT calculations revealed that 1,5‐Pd migration likely proceeds via both concerted PdII and stepwise PdIV routes. Asymmetric synthesis of the chiral triptycenes, as well as optical resolution, and further transformation are also reported.
Treatment of 1,6‐azaeneyne compounds with Ph3SnH resulted in the stereoselective formation of 5‐(E)‐alkylidene‐2,3‐cis‐piperidine in moderate to good yields. Intermediate products including methylenepyrrolidine and stannomethylene pyrrolidine were also detected in the reaction mixture, suggesting that the reaction progressed via a highly cumulated radical cascade process involving sequential six radical processes, i.e. radical addition, 5‐exo cyclization, substitution (1,4‐tin migration), 3‐exo cyclization, ring cleavage of cycloprolane, and hydrogen abstraction from Ph3SnH. The product distribution depended on the lower Ph3SnH concentration, resulting in higher piperidine yields. The E/Z selectivity of the exo‐methylene unit was also sensitive to the reaction temperature. The vinylic triphenyltin group was converted into hydrogen and iodine. A kinetic analysis of the reaction indicated that the 1,4‐tin migration and ring expansion progressed as irreversible reactions and that their reaction rates were large enough to progress the cascade reaction smoothly and to prevent side reactions such as hydrogen abstraction from Ph3SnH.
Dibutylmethyltin hydride and tert‐butyldibutyltin hydride were employed to examine radical cascade reaction of aza‐1,6‐enyne for the preliminary estimation of homofugality between alkyl groups by product distribution analysis. Use of either dibutylmethyltin hydride or tert‐butyldibutyltin hydride preferentially produced butylmethylstannolane, in which butyl group was mainly substituted by vinyl radical.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.