Various 1-hydroxyindoles carrying a nitro, methoxycarbonyl, or benzyloxy group at the 4 position were prepared by the controlled reduction of 6-substituted trans-β-dimethylamino-2-nitrostyrenes with either aqueous titanium (III) chloride or zinc in aqueous ammonium chloride. The stability of 4-substituted 1-hydroxyindoles decreased in the following order : 4-nitro-»4-methoxycarbonyl->4-benzyloxy-1-hydroxyindole. This result clearly indicates that an electron-withdrawing group at the 4-position can stabilize the 1-hydroxyindole structure. It was also found that 4-hydroxy-and 4-benzyloxy-indole were readily accessible by the reduction of 6-benzyloxy-2-nitrophenyl acetaldehyde. A unique route to 4-or 7-aminoindole from cinnoline is also described.
通过6-取代的反式-β-
二甲氨基-
2-硝基苯乙烯在控制条件下分别与
三氯化钛(III)
水溶液或
氯化铵水溶液中的
锌进行还原反应,制备了在4位带有硝基、甲氧羰基或苄氧基的各种
1-羟基吲哚。4-取代的
1-羟基吲哚的稳定性按以下顺序递减:4-硝基->4-甲氧羰基->4-苄氧基-
1-羟基吲哚。这一结果清楚地表明,4-位上的吸电子基团可以稳定
1-羟基吲哚结构。还发现,
4-羟基-和4-苄氧基-
吲哚可通过6-苄氧基-2-
硝基苯基
乙醛的还原反应方便地获得。同时,还描述了一种从肉桂啉制备4-或
7-氨基吲哚的独特途径。