Synthesis of 7-hydroxy-6,7-dihydro-indole and 6′,7′-dihydro-3,7′-biindole derivatives from domino reactions of arylglyoxals or methyl ketones with enamines

Abstract

A series of interesting 7-hydroxy-2-aryl-6,7-dihydro-indol-4(5H)-ones 3 was successfully synthesized in moderate to good yields by the domino reactions of different arylglyoxals 1 with enamines 2 under catalyst-free conditions. 7-Hydroxy-2-aryl-6,7-dihydro-indol-4(5H)-ones 3 could also be prepared in moderate yields by the iodine-promoted one pot-two step reactions of methyl ketones 6 with enamines 2. The reaction of 3a with N-methyl indole 7a in the presence of PTSA afforded 2′-aryl-6′,7′-dihydro-[3,7′-biindol]-4′(5′H)-ones 8a in 81% yield. In addition, 3,7′-bis-indoles 8 could also be observed in 47–73% yields by one pot domino reaction of arylglyoxals 1 with enamines 2 and indoles 7 over two steps. This protocol provides a simple and practical method to construct diverse 7-hydroxy-6,7-dihydro-indole derivatives 3 and 3,7′-bis-indoles 8 from easily obtained starting materials.