Domino addition/annulation of δ-alkynylaldehydes and oxygen nucleophiles: a new entry to [1,4]oxazino[4,3-a]indoles
摘要:
The unusual [1,4]oxazino[4,3-a]indole nucleus was prepared, under mild reaction conditions, by reacting 1-alkynyl-1H-indole-2-carbaldehydes with various alkoxides, generated in situ from the corresponding alkyl, benzyl, allyl and propargyl alcohols. (c) 2005 Elsevier Ltd. All rights reserved.
Intramolecular Cyclization of δ-Iminoacetylenes: A New Entry to Pyrazino[1,2-a]indoles
摘要:
The synthesis of the pyrazino[1,2-alpha]indole nucleus was achieved by intramolecular cyclization of several 2-carbonyl-1-propargylindoles in the presence of ammonia. The reaction conditions were optimized using microwave heating and a pool of catalysts. Cyclization of 1-alkynylindole-2-carbaldehydes was easily accomplished under standard heating conditions, whereas microwave heating contributed to reduced reaction times and improved overall yields. Moreover, a fine-tuning of the microwave irradiation time made possible the selective synthesis of both pyrazino[1,2-alpha]indole isomers. TiCl4 proved the catalytic system of choice to achieve pyrazinoindoles in satisfactory yields starting from 1-alkynyl-2-acetylindoles and 1-alkynyl-2-benzoylindole derivatives. Also in these cases, microwave heating contributed to faster reactions and improved yields. The uncatalyzed versus catalyzed reaction mechanism is discussed.
Intramolecular cyclization of 2-acyl-l-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleus. (C) 2003 Elsevier Science Ltd. All rights reserved.