Easy access to N-aryl, N-heteroarylbenzoxazolinones and 4-aza analogues via Diels–Alder cycloaddition reactions

Easy Access to New Heterocyclic Systems: 1,4-Oxazine and Substituted 1,4-Oxazines

“…The reductive cleavage of the vinyl phosphate group was also investigated. We had previously shown that it was possible to reduce the vinylphosphate moiety by adapting a procedure first described by Cacchi. 2b, Hence, treatment of bisvinylphosphate 3 with triethylammonium formate, palladium acetate, and triphenylphosphine in THF led to the core heterocyclic system 5 in 70% yield (Scheme ). To the best of our knowledge, so far, there has been no description in the literature of 1,4-oxazine 5 .…”

“…In order to take advantage of these 1,4-oxazine scaffolds, we next focused on studying their reactivity toward organometallic reagents. On the basis of our previous results in the 1,4-benzoxazine series,2c we investigated the functionalization of these 1,4-oxazine derivatives by means of lithium anion species derived from a hydrogen−metal interchange in the presence of alkylithium reagents. This methodology, which offers the opportunity to easily introduce various substituents on these compounds, should be particularly useful for the development of libraries of biologically relevant 1,4-oxazine derivatives.…”

“…Identifying improved methods for heterocycle synthesis and, essentially, giving access to new heterocyclic scaffolds are of prime importance. In connection with our efforts to develop synthetic routes to nitrogen-containing heterocyclic derivatives, , and particularly six-membered ones, we intended to prepare the oxazine systems I or II (cf. Figure ) and various substituted derivatives of this kind (compounds III , IV , and V ).…”