Stereoselective Synthesis of Pyrido- and Pyrrolo­[1,2‑c]­[1,3]oxazin-1-ones via a Nucleophilic Addition–Cyclization Process of N,O‑Acetal with Ynamides

An efficient asymmetric approach to access functionalized pyrido- and pyrrolo­[1,2-c]­[1,3]­oxazin-1-ones has been developed through a nucleophilic addition–cyclization process of N,O-acetal with ynamides. A number of substituted ynamides 8a–8o and 3-silyloxypyrrolidine or piperidine N,O-acetals 6a, 7 were amenable to this transformation, and the desired products 9a–9o, 10a–10m were obtained with excellent regioselectivities and outstanding diastereoselectivities. Moreover, chiral ynamides 14a–14f could also experience this addition–cyclization process to afford products 15a–15f in excellent yields.