Azokupplungen an 3,4-Dimethoxyfuran

Diazo coupling of 3,4-dimethoxyfuran with aryl diazonium ions 3,4-Dimethoxyfuran ( 1 ) easily reacts with aryl diazonium chloride in aqueous pyridine in an expected 1, 4-addition reaction. From the isolable primary addition product pyridine is displaced by alcohols, phenols or thiols to yield 4-alkoxy- or 4-phenoxy- or 4-thiophenoxy-derivatives of 2,3-dimethoxy-2-buten-4-olide ( 3 ). Attempts to convert them into azo compounds by a base catalysed 1, 6-elimination reaction failed. Oxidation of 3a and 3c with DDQ results in the formation of the mono p-nitrophenylhydrazone of 3, 4-dimethoxymaleic acid anhydride. On the other hand, the thiophenoxy compound 3g is smoothly converted by MnO₂ into the authentic furan-2-azobenzene derivative 5 .