Synthesis of 3,4-dihydro-2H-1,4-benzoxazines and their Oxo Derivatives: A Review

Aryl-fused 1,4-oxazine derivatives have been recently studied with growing interest due to their pesticidal, especially antifeedant and antifungal, as well as pharmacological activities. These promising biological properties have encouraged the development of efficient synthetic strategies toward 3,4-dihydro-2H-1,4-benzoxazines and their 2-oxo, 3-oxo and 2,3-dioxo derivatives. Most of the available methods for preparing these heterocycles involve the annulation of a 1,4-benzoxazine ring to an arene scaffold. The present review reports a number of representative examples of the novel and modern synthetic strategies used for the ring closure reactions involving transition metal catalysis, microwave-assistance, metal-free or solid-state processes. Some of these syntheses are carried out in mild reaction conditions, employing room temperature and/or environmentally friendly solvents.