1-Hydroxy-5- and -6-Nitroindole-3-carbaldehydes, and Analogs

Compounds (5a and 6a, Scheme 2) are useful synthetic intermediates as shown later in Sect. 3.3.2. In order to obtain 5a, three routes are explored starting from indoline (7) [11]. Since 1-hydroxy-6-nitroindole (8a) is readily available in two steps from 7 according to our method [12], the Vilsmeier-Haack reaction of 8a is first attempted in vain and gives disappointing results with the formation of many products.

Scheme 4 Two Steps

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