Synthesis of Cyclic Enaminones via Ketene Cyclization

Significance

Reported is an efficient three-­component synthesis of dihydropyridones 5 from bromodiazoacetone 1, primary amines 2, and alkynes 4 through an aza-Michael reaction, Wolff rearrangement and nucleophilic ketene cyclization. Based on previous work (H. Seki, G. I. Georg J. Am. Chem. Soc. 2010, 132, 15512), the Wolff rearrangement required a silver catalyst to generate the intermediate ketene involved in the cyclization. The synthesis of the amino diazoketone 3 ­involves the use of an excess of primary amine. Various alkyl amines 2 as well as a chiral amine are tolerated. The aza-Michael reaction of 3 to the alkynes 4 and subsequent Wolff rearrangement ­involves a one-pot procedure, which lead to the enaminones 5 in good yield using Ag₂O or PhCO₂Ag as catalyst.