Regioselective Functionalization of 9,9-Dimethyl-9-silafluorenes by Borylation, Bromination, and Nitration

Abstract

Despite the utility of 9-silafluorenes as functional materials and as building blocks, methods for efficient functionalization of their backbone are rare, probably because of the presence of easily cleavable C–Si bonds. Although controlling the regioselectivity of iridium-catalyzed direct borylation of C–H bonds is difficult, we found that bromination and nitration of 2-methoxy-9-silafluorene under mild conditions occurred predominantly at the electron-rich position. The resulting product having methoxy and bromo groups can be utilized as a building block for the synthesis of unsymmetrically substituted 9-silafluorene-containing π-conjugated molecules.

Recent Advances in C–H Functionalization of Pyrenes

“…Then, with the help of the sulfate dianion, the desired C-H phosphonylation product is generated. Takai et al disclosed [76] the nitration of pyrene under mild conditions using Fe(NO 3 ) 3 •9H 2 O, which generates a nitrogen dioxide free radical species, giving product 19a with a 89% yield. This C-H nitration process does not need any acidic promoters, pyridine-based-directing groups, ionic liquids, or supported metal nitrates (Scheme 12).…”

“…Functionalization of the C1 and C6 positions of pyrenes. Direct C-H phosphonylation of pyrenes via visible light photoredox catalysis, C-H nitration, and amination of the pyrene core[75][76][77].…”

Regioselectivity Control in Spirobifluorene Nitration under Mild Conditions: Explaining the Crivello’s Reagent Mechanism

“…Crivello introduced the use of mixtures of ammonium nitrate and trifluoroacetic anhydride (TFAA) to nitrate a variety of aromatic compounds at room temperature in good yield . Trifluoroacetyl nitrate seems to be the effective reactive nitrating agent that gives rise to nitronium ions upon heterolytic dissociation of the oxygen-nitrogen bond. , Despite its efficacy, the method has been rarely applied to compounds with extended aromaticity, whereas metal nitrate-mediated nitration of aromatic substrates is a current field of research . It is worth to emphasize that Crivello tested several dinitrate salts as the source of nitrating agents.…”

Significant energy gap modulation of sulfone-substituted benzosiloles: enhanced brightness and electron affinity for chemical vapor sensing, fingerprint detection and live-cell imaging

“…19 A few facile and innovative synthetic strategies for benzosilole derivatives have been established for developing novel structures and functionalities in recent years. 17,[20][21][22][23][24][25][26][27][28][29][30] However, on the basis of the developed advantages, it still remains a great challenge to further improve the performance of benzosilole derivatives, that is, extending the fluorescence to longer wavelengths with high color purity and brightness, which is of vital importance to the currently widespread applications. [31][32][33][34][35] On the other hand, the emission colors and brightness could be significantly tuned by grafting sulfone groups onto the conjugated molecules.…”