Copper-catalyzed synthesis of heterocycles via oxidative ring closure reactions of aromatic nitriles with diaryliodonium salts

Abstract

Scheme 4. Recently, the microwave-assisted palladium-catalyzed synthesis of imino-1,3benzoxazines was reported by Batra 22 et al. They also utilized isonitriles as starting materials which were reacted with 2-bromophenylureas in the presence of Pd-ligand and cesium carbonate base.The first synthesis of imino-1,4-benzoxazines ( 27) was reported by Weidinger and Kranz 23 in 1964 by the condensation of ortho-aminophenols (25) with oxalyl bismethylimidate (26) under acidic conditions (Scheme 5). Scheme 5. Preparation of 2-imino-3-amino-1,4-benzoxazinesIn 2009, González 24 et al. developed a three-component synthesis for the construction of 2-imino-1,4-benzoxazine derivatives (31) from salicylaldehydes (28), ortho-aminophenols (29) and arylisocyanides (30) in toluene in the presence of ammonium-chloride (Scheme 6). The desired iminobenzoxazine derivatives could also be obtained by preparing the putative Schiff base intermediate followed by addition of the isonitrile, but in that case, more vigorous conditions were required.