Synthesis of Annulated γ-Carbolines and Heteropolycycles by the Palladium-Catalyzed Intramolecular Annulation of Alkynes
摘要:
A variety of N-substituted 2-bromo-1H-indole-3-carboxaldehydes incorporating an alkyne-containing tether on the indole nitrogen have been converted to the corresponding tert-butylimines, which have been subjected to palladium-catalyzed intramolecular iminoannulation, affording various gamma-carboline derivatives with an additional ring fused across the 4- and 5-positions in good to excellent yields. When the tethered carbon-carbon triple bond is terminal or substituted with a triethylsilyl group, the iminoannulation generates a tert-butyl-gamma-carbolinium salt as the major product. The palladium-catalyzed intramolecular annulations of N-substituted 2-bromo-1H-indole-3-carboxaldehyde, methyl 2-iodo-1H-indole-3-carboxylate, and 2-iodo-3-phenyl-1H-indole containing a phenylpentynyl tether produce the corresponding heteropolycycles in moderate to good yields.
In the presence of PdCl2(PPh(3))(2) and Et(3)N, chloroenynes and chlorodienes react rapidly under mild conditions with various Grignard reagents to give isomerically pure conjugated enynes, dienes, dienynes and trienes in good isolated yields. (C) 1997 Published by Elsevier Science Ltd.