The palladium(0)-catalysed coupling of 2-haloquinoxalines with alkynes, addition of one mol equivalent of bromine to the 2-alkynylquinoxalines thus produced and then reaction of the resulting dibromides with dipotassium trithiocarbonate produces thieno [2,3-b]quinoxalines.
Dedicated to Professor Otto Meth-Cohn on the occasion of his 65th birthday (received 12 Sep 00; accepted 03 Oct 00; published on the web 11 Oct 00) Abstract 8-Bromo-7-methoxyisoquinoline was produced by Jackson's modification of the Pomeranz-Fritsch ring synthesis accompanied by 8-bromo-3-(8-bromo-7-methoxyisoquinolin-4-yl)-1,2,3,4-tetrahydro-7-methoxy-2-(4-methylphenylsulfonyl)isoquinoline. A mechanism for the formation of the latter is suggested. The ready formation of secondary amine-BH 3 complexes was noted and the X-ray crystal structure of N-(2-bromo-3-methoxybenzyl)aminoacetaldehyde dimethyl acetal boranedetailed.
Synthesis of Thieno [2,3-b]quinoxalines and Pyrrolo[1,2-a]quinoxalines from 2-Haloquinoxalines.-Thienoquinoxalines (V) and (XII) are prepared by coupling of 2-haloquinoxalines with alkynes, followed by bromination of the resulting alkynyl derivatives, and reaction of the dibromoalkenes with Na 2 CS 3 . Alkynyl derivatives (XIII) and (XVI) undergo ring closure in addition to bromination by treatment with bromine to afford pyrroloquinoxalines (XIV) and (XVII). The corresponding dibromoalkenyl quinolines, pyrazines and pyrimidines fail to induce thiophene ring formation. -(ARMENGOL, MONTSERRAT; JOULE, JOHN A.; Perkin 1 (2001) 9, 978-984; Dep. Chem., Univ. Manchester, Manchester M13 9PL, UK; EN)
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