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Fischer Indole reactions and their utility in dyestuff chemistry

机译：费歇尔吲哚反应及其在染料化学中的应用

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Ahydrazone obtained from an aldehyde or ketone with an arylhydrazine having a free ortho position forms an indole when heated at 180°- 200° with an acidic catalyst like anhydrous zinc chloride, polyphosphoric acid, sulphuric acid etc. This reaction, commonly referred to as Fischer Indole synthesis, is the most important method for the preparation of indoles (Chart 1), although it fails for the synthesis of indole itself. The reaction is an intramolecular condensation reaction with the elimination of ammonia molecule. Various mechanisms have been suggested for the reaction. A widely accepted one is given in Chart 2. A large number of catalysts have been employed; examples are concentrated sulphuric acid, cuprous chloride, zi.nc chloride, boron trifluoride or polyphosphoric acid. The yields of substituted indoles are generally high. Iso-topic tracer studies have indicated that it is the nitrogen furthest from the benzene ring that is lost as ammonia. In the initial stage of the reaction the double bond migrates one position fur- ther away from the benzene ring, and the latter is then attacked by the doubly bonded carbon giving the diamino compound which subsequently rearranges and cyclises with loss of ammonia. The mechanism is very similar to o-benzidine rearrangement. The synthetic utility of Fischer indole synthesis include the following (ⅰ) Synthesis of indole and its derivatives (ⅱ) Synthesis of tryptamine (ⅲ) Synthesis of carbazoles.
机译：由醛或酮与具有游离邻位的芳基肼制得的在与酸性催化剂（如无水氯化锌，多磷酸，硫酸等）在180°-200°加热时会形成吲哚。该反应通常称为Fischer吲哚合成是吲哚制备的最重要方法（图1），尽管吲哚本身无法合成。该反应是消除氨分子的分子内缩合反应。已经提出了各种反应机理。图2给出了一种被广泛接受的催化剂。已经使用了大量的催化剂。例子是浓硫酸，氯化亚铜，氯化锌，三氟化硼或多磷酸。取代的吲哚的产率通常很高。同位素示踪研究表明，距苯环最远的氮以氨的形式流失。在反应的初始阶段，双键从苯环向另一个位置迁移，然后后者被双键碳攻击，生成二氨基化合物，随后重排并环化而失去氨。其机理与邻联苯胺重排非常相似。 Fischer吲哚合成的合成用途包括：（ⅰ）吲哚及其衍生物的合成（ⅱ）色胺的合成（ⅲ）咔唑的合成。

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