Visible-light-promoted synthesis of gem-dihaloenones

Visible light-promoted strategies were developed for the synthesis of gem-dihaloenones using alkynes and polyhalomethanes as the starting materials. The methods produce a broad range of gem-dibromoenones and gem-dichloroenones without using photocatalysts or additives, such as bases and oxidants. This is the first example of a photocatalyst-free strategy for the photo-promoted synthesis of gem-dihaloenones. These protocols were compatible with various terminal and internal alkynes and were effective in gram-scale experiments. The mechanistic investigations suggested that the tertiary carbon center radical could be a critical intermediate, undergoing beta-scission of the C-O bond to form the methyl radical, followed by hydrogen atom transfer (HAT) to produce methane.