Copper-Catalyzed Reaction of Ketenimine and in Situ Generated Immonium Ion: Access to α,β-Unsaturated Amidines

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A Cu-catalyzed three-component reaction of alkyne, azides (sulfonyl or phosphoryl azides), and N,N-dialkyloxyformamide dialkyl acetal via electrophilic addition of immonium ion to copper ketenimine is reported. This new protocol for the preparation of α,β-unsaturated amidine derivatives appears to offer high yield, mild conditions, and wide substrate scope. The reaction might involve the processes of copper ketenimine intermediate formation, electrophilic addition, and isomerization.