A regioselective, convergent, and additive-free approach for the synthesis of pyrido[1,4]oxazocines

Research interest in the construction of fused medium-ring [1,4]oxazocines has led to rapid growth in the discovery of biologically active compounds. Herein, the tandem reactions of 4-Cl- and 2-Cl-substituted 3-(oxiran-2-yl)pyridines with a variety of ethanolamines for one-pot synthesis of pyrido[1,4]oxazocines have been developed under additive-free conditions. Note that this process represents a regioselectivity profile in view of the fact that a SN2-type ring-opening reaction of the oxirane moiety with the amino group and a SNAr-type etherification of the 4-chloro or 2-chloropyridine moiety with the hydroxyl group proceed, respectively. Good substrate compatibility, mild reaction conditions, and atom economy make this protocol a convergent and efficient choice for accessing uncommon bicyclic structures. Furthermore, gram-scale reactions and downstream derivatization of the resulting pyrido[1,4]oxazocines are performed. The synthesis of pyrido[1,4]oxazocines from 4-Cl- and 2-Cl-substituted 3-(oxiran-2-yl)pyridines and ethanolamines was developed under additive-free conditions in a regioselective and convergent manner.