Visible‐Light Induced Radical Silylation for the Synthesis of Dibenzosiloles via Dehydrogenative Cyclization

Abstract

A visible‐light induced radical silylation to dibenzosiloles from biarylhydrosilanes is described. The products were obtained in satisfactory yields under mild and water/air compatible conditions, providing an efficient and practical method for the synthesis of difunctionalized siloles by using a cheap organic dye photocatalyst. The method is tolerated by a wide range of functional groups and has a broad substrate scope. Light/dark experiments and quantum yield measurements provided support for a photocatalytic pathway rather than a chain process.magnified image

Advances in Synthesis of π-Extended Benzosilole Derivatives and Their Analogs

“…In 2017, Jiang et al disclosed an efficient synthesis of dibenzosiloles 154 from biarylhydrosilanes 153 via a visible-light induced radical silylation process. In the presence of rose bengal as photocatalyst, dibenzosilole derivatives were prepared in good yields at room temperature under water/air compatible conditions (Scheme 37) [64]. Several studies on light/dark experiments and quantum yield measurements provided valuable evidences supporting the proposed photocatalytic mechanism from 155 to 159 (Scheme 38).…”

Preparation of Polyfunctional Biaryl Derivatives by Cyclolanthanation of 2‐Bromobiaryls and Heterocyclic Analogues Using nBu2LaCl⋅4 LiCl

“…Silafluorenes of type 5 were previously prepared by conventional nucleophilic substitution reactions or transition‐metal‐catalyzed couplings using 2,2′‐difunctionalized biaryl precursors such as halides, silanes, triflates, or boronic acids . Alternatively, intramolecular C−H silylation of 2‐biarylsilanes toward silafluorenes has been developed by a number of groups, using 1) a rhodium‐catalyzed synthesis as demonstrated by Kuninobu and Takai, He, and Mitsudo and Suga, 2) a sila‐Friedel–Crafts (S E Ar) reaction as shown by Kobayashi and Kawashima, Ingleson, and Oestreich, and 3) a radical silylation reaction as reported by Studer, Li, and Jiang . Palladium‐catalyzed cyclocarbonylation of o ‐halobiaryls with CO leading to fluoren‐9‐ones of type 6 has been reported by Larock, and other carbonyl sources such as furfural, formaldehyde, and phenyl formate have been employed in this cyclocarbonylation .…”

Herstellung von polyfunktionellen Biarylderivaten durch Cyclolanthanierung von 2‐Bromobiarylen und heterocyclischen Analoga unter Verwendung von nBu2LaCl⋅4 LiCl

“…Silafluorene vom Typ 5 wurden bisher über konventionelle Substitutionsreaktionen oder übergangsmetallkatalysierte Kupplungen unter Verwendung von 2,2′‐difunktionalisierten Biarylvorstufen (wie zum Beispiel Halogenide, Silane, Triflate oder Boronsäuren) hergestellt . Alternativ wurden intramolekulare C‐H Silylierungen von 2‐Biarylsilanen von mehreren Forschungsgruppen entwickelt unter Verwendung von i) Rhodiumkatalyse, gezeigt von Kuninobu und Takai, He, als auch Mitsudo und Suga, ii) Sila‐Friedel‐Crafts‐Reaktionen (S E Ar), gezeigt von Kobayashi und Kawashima, Ingleson, und Oestreich, oder iii) radikalischen Silylierungsreaktionen gezeigt von Studer, Li, und Jiang …”