Functionalization of Indole and Pyrrole Cores via Michael-Type Additions

Use of the Nascent Isocyclic Ring to Anchor Assembly of the Full Skeleton of Model Chlorophylls

“…The subsequent Nazarov cyclization and electrophilic aromatic substitution proceed in the presence of trivalent lanthanide catalysts under more forcing conditions (80 °C). Nazarov reactions find increasing use in heterocyclic chemistry − but have been employed infrequently with pyrroles bearing a propenoyl group at the 3-position. ,− The intramolecular juxtaposition of the carboxaldehyde of ring B and the pyrrolic unit of ring A in III likely facilitates the reaction of these intrinsically lesser reactive species in the electrophilic substitution giving rise to IV . Further studies are required to probe the sequence of events leading from III to V , to explore milder conditions for the Nazarov and accompanying reactions (including substitutes for InX 3 ), and ultimately to assess whether this general approach can accommodate the array of substituents present in native chlorophylls.…”

Addition of N–H bonds to iridium: Synthesis and characterization of N–Ir–H complexes and the observation that an iridium N-bonded indole ring becomes activated for Michael addition to alkynes

“…Free indole does not react with these alkynes under the same conditions. Usually, a Lewis acid is required for addition ð7Þ to the three position of indole [32]. Therefore, the coordinated indole ring in 2b must be more electron rich than in uncoordinated indole providing a more activated ring for the Michael-type addition.…”

An efficient synthesis of 3-substituted indole derivates under ultrasound irradiation

“…4,135.5,133.4,128.5,127.8,127.0,125.6,121.5,121.1,119.9,118.6,116.2,110.7,107.3,77.4,35.5, 7,144.7,135.4,132.6,131.4,126.9,121.4,119.84,119.76,118.6,114.4,110.7,110.4,109.1,79.0,55.9,40.3, 0, 146.6, 135.4, 133.4, 132.6, 126.8, 121.4, 120.0, 119.8, 118.6, 110.7, 109.0, 108.23, 108.20, 101.1, 78.8, 40.3, 12. 133.7, 129.2, 129.0, 127.7, 125.9, 122.6, 121.4, 113.7, 113.4, 112.9, 79.1, 40.7. 0,135.1,131.0,129.0,127.9,125.7,122.5,121.6,115.9,114.5,113.3,112.8,79.6, 129.0, 128.9, 128.1, 125.6, 125.0, 123.0, 121.6, 121.4, 116.1, 113.4, 113.3, 112.8, 77.8, 35.8.…”

“…Owing to the great structural diversity and wide-ranging biological activity of indole derivates [3], construction and functionalization of indole rings continue to attract the interest of both synthetic and pharmaceutical chemists. The conjugate addition of indoles to Michael acceptors provides easy access to 3-substituted indole derivates [4], which are important building blocks for the synthesis of biologically important compounds. Among various types of Michael acceptors, nitroalkenes are undoubtedly the strongest and particularly versatile one [5], since the nitro group is a powerful electron-withdrawing substituent and it may be transformed into a legion of diverse functionality [6].…”