Enolethers. XX. Synthesis of azepino[4,5‐b]quinoxalines and pyridopyrazino[2,3‐d]azepines

Abstract 1,6‐Diethoxy‐1,5‐hexadiene‐3,4‐dione (1) reacts with primary amines 3 and ammonia respectively in a molar ratio of 1:1 to give mainly aminoalkyl‐ and small amounts of bis(aminoalkyl)‐1,5‐hexadiene‐3,4‐diones 4 and 2, respectively. On heating in dichlorobenzene above 150° the mixtures of 2 and 4 cyclize to yield 1‐alkyl‐1H‐azepine‐4,5‐diones 5 by elimination of ethanol or amine. 3H‐3‐Alkylazepino[4,5‐b]‐quinoxalines 7, 8, 10 and 12 are easily accessible by condensation of the diketones 5a and b with various substituted o‐phenylenediamines 6, 9 and 3,3′,4,4′‐tetraaminobiphenyl (11) in p‐xylene or n‐butanol. 8‐Isopropylpyridopyrazino[2,3‐d]azepines 14 were obtained by condensation of 5b with pyridinediamines 13 in p‐xylene. The azepine‐4,5‐diones 5a‐c can be hydrogenated selectively by sodium borohydride in ethanol at room temperature to give the azepin‐4‐ol‐5‐ones 15a‐c.