Radical Cyclization:Efficient Routes To Synthesize Dihydrobenzofuran Or 6-Benzyl Henanthridine Derivatives

The cyclic compounds have a very wide range of applications in synthetic materials,natural products,pharmaceutical drugs and other agricultural fields.But there is difficult to prepare.Researchers have found that less raw materials for preparing them and have complicated steps,various byproducts,low yields,harsh reaction conditions.However,radical cyclizations followed by trapping with radical scavengers have been proven to be a powerful and versatile way forconstruction of mono-or polycyclic compounds bearing additional functional groups.Mainly due to to it's mildreaction conditions,strong persistence,low polarity of the solvent and short reactiontime,radical cyclizationreactions have become an increasingly powerful andversatile tool in chemical synthesis in recent years.The main contents are as follows:Part one:A copper-catalyzed radical carbochlorination or carbobromination is reported.Nitrite is used asdiazotization reagent and hydrohalogenic acid provideshalogen source at the same time as the acidifying reagent.Aryl amines are transformed in situ to the corresponding aryl diazonium salts which in turn act as aryl-radical precursors,then aryl diazonium salts are catalyzed by coppersalts to generate aryl radicals,which undergo typical 5-exo and 6-exo cyclization reactions and the cyclized alkyl radicals are then halogenated in a chain reaction leading to the synthesis of(3-halomethyl)-1,2-dihydrobenzofuran derivates in a high efficient way.The readyavailability of starting materials,easy-handle protocol,and cheap halogen sources make thecurrent methodology particularly interesting for synthesis.Part two:A novel method for the synthesis of 6-benzyl phenanthridines derivates starting with readily prepared 2-isocyanobiphenyls and available toluene.The sequential radical addition-cyclization strategy represents a practical route to access 6-benzyl phenanthridines derivates.Various functional groups such as methoxy,fluoro,chloro,bromine and tert-butyl were tolerated well under the reaction conditions.The transition metal-free conditions afforded environmentally friendly approach,which makes this strategy more attractive.