Phosphine-Catalyzed Chemoselective [4+3] Cycloaddition of Alminine Esters and β′-acetoxy Allenoates for Divergent Synthesis of Azepines

Text. A general method for the synthesis of structural diversity and complexity of azepines from aldimine esters and beta '-acetoxy allenoates is reported. Under phosphine catalysis, a [4+3] cycloaddition for the formation of 1,3-dihydro-2H-azepine-2,2,4-tricarboxylates was achieved with broad substrate scope under mild reactions. A switchable process was given and a variety of important 2,3-dihydrochromeno[4,3-b]azepin-6(1H)-ones were selectively formed when the reaction was performed in the presence of Cs2CO3 and PPh3, which involved an intramolecular ester group migration and subsequent lactonization of 1,3-dihydro-2H-azepine-2,2,4-tricarboxylates. Besides easy handle process, high synthetic value of resulting products, it is worth to note that this work showed the novel example of 1,5-ethoxycarbonyl migration.