Palladium-Catalyzed Synthesis of 2,3-Di-substituted Indoles from Aryldiazonium Salts

Significance

Based on previous result from the same laboratory (S. Cacchi et al. Org. Lett. 2008, 10, 1597), a palladium-catalyzed synthesis of free NH 2,3-disubstituted indoles 3 by the reaction of arenediazonium tetrafluoroborate 1 with 2-alkynyltrifluoroacetanilides 2 has been developed. An ­iododediazonization reaction is required in the presence of TBAI in order to generate ‘ArPdI’ ­species (K. K. Laali and co-workers J. Org. Chem. 2008, 73, 316) that coordinate to the triple bond followed by intramolecular aminopalladation-­reductive elimination to give the indole 3. After development of the optimized conditions [Pd(PPh₃)₄, K₂CO₃, and TBAI], the scope of this reaction was investigated with a variety of substituted alkynes and arenediazonium salts to afford the given results.