Synthesis of Two-Dimensional C–C Bonded Truxene-Based Covalent Organic Frameworks by Irreversible Brønsted Acid-Catalyzed Aldol Cyclotrimerization

The synthesis of new C–C bonded two-dimensional (2D) covalent organic frameworks (COFs) is highly desirable. Here, a simple but effective synthetic strategy has been developed using an irreversible Brønsted acid-catalyzed aldol cyclotrimerization reaction by virtue of truxene as a linkage. Nonolefin C–C bonded 2D truxene-based covalent organic frameworks (Tru-COFs) were constructed by polymerization of 1,3,5-triindanonebenzene (TDB). The structure formation was confirmed by wide-angle X-ray scattering, Fourier-transform infrared spectroscopy, and solid-state 13C CP/MAS NMR. The results showed that the Tru-COFs were porous (645 m2/g) and chemically stable. Benzyl methylene in conjugated Tru-COFs more effectively produced photoinduced radicals than the model truxene compound. Due to the radical photoresponsiveness, Tru-COFs were efficient catalysts for photocatalytic oxidation of sulfides. We expect that this will provide a new synthetic methodology to obtain C–C bonded functional 2D COFs.

Vinylindenes and some heteroanalogues in the Diels-Alder reaction. VIII. 1-Benzyl-3-vinylindole as a diene

1-Benzyl-3-vinylindole gives stable adducts resulting from [2+4] cycloadditions with 1,4-benzo-quinone, 1,4-naphthoquinone, N- phenylmaleimide and maleic anhydride. Vicinal 1H n.m.r. coupling constants for protons on the cyclohexene rings are used to show that the first two adducts probably have half-chair conformations, while the last have boat conformations. Non-equivalence of the benzyl methylene protons of the benzoquinone adduct has been shown to display a surprising temperature dependence. The adduct of the vinylindole and ethenetetracarbonitrile is shown to be a cyclobutane resulting from a [2+2] cycloaddition.