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.