Quinolines, functionalization by directed

The formation of quinolines by irradiation in alcohols has been known from Ciamieian s times actually, the components for a Skraup synthesis are generated in situ by photoredox processes. A dedieated system has been devised, based on an arenesulfonic acid functionalized mesoporous silica decorated with titania. The examination has been extended to various nitrobenzenes and different Ti02 catalysts, and shown to be quite general, though with a different product distribution. Platination of the catalyst reduced the imine function and directed the process toward N-allqrlation. The related reaction leading to benzimidazoles from o-nitroanilines has been likewise optimized from the preparative point of view. ... 

A number of other heterocycllcs have been similarly studied and shown by H nmr, to produce quaternary ammonium salts with living polyTHF.2- Moreover, their rates of reaction are a direct function of their basicities, the following order of reactivities being observed ethyl pyridine > pyridine > isoquinoline > quinoline > acridine. Aliphatic tertiary amines also react in the same way the order of reactivities was found to be triethylame > tributylamlne > dlethylanillne. In all cases studied, the quaternary ammonium salt once formed did not exchange with any excess oxonium lone. 

The Pd-catalyzed oxidation of unfunctionalized C-H bonds has recently been described by Sanford. These reactions lead to the direct, regioselective installation of hydroxyl groups or halogen atoms onto aromatic and heteroaromatic ring systems. For example, benzo[//]quinoline is selectively converted to 10-chlorobenzo[A]quinoline upon treatment with catalytic Pd(OAc)2 and NCS [103]. As shown below, these transformations are also effective for the installation of oxygenated functional groups including acetates and alkyl ethers. The oxidative functionalization of. sy/ C-H bonds has also been achieved [104]. 

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