Beiträge zur Chemie der 4-Hydroxyindol-Verbindungen 10. Mitteilung über synthetische indolverbindungen [1]

✍ Scribed by F. Seemann; E. Wiskott; P. Niklaus; F. Troxler

• Publisher: John Wiley and Sons
• Year: 1971
• Tongue: German
• Weight: 576 KB
• Volume: 54
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19710540805

✦ Synopsis

Abstract

Catalytic hydrogenation of 4‐benzyloxyindoles does not stop at the hydroxyindole stage, but slowly leads to the 4,5,6,7‐tetrahydro‐4‐ox‐indoles 3. Some procedures for the selective preparation of 4‐hydroxyindoles 2 are described. When 4‐benzyloxy‐3‐(1‐hydroxyimino‐ethyl)‐indole (4c) is warmed with trifluoroacetic acid, cleavage of the ether results as well as partial benzylation of the free hydroxyindole in the position 5 (5a, 5b); no Beckmann rearrangement is observed. Esters of 4‐benzyloxy‐indole‐2‐carboxylic acid are formylated with POCl~3~/dimethylformamide in the 7‐position to give 7a; in the corresponding dimethylamide, on the other hand, the formyl group enters the 3‐position to give 8. Both 4‐ and 7‐hydroxyindole are oxidized with Frémy's salt to the 4, 7‐quinone 13; on reduction this yields 4, 7‐dihydroxyindole 14, which is tautomerized by base‐catalysis to 5, 6‐dihydro‐4, 7‐dioxo‐indole 15. The course of the etherification of 4‐hydroxyindoles with epichlorohydrin and related compounds is described, and the resulting side‐chains are characterized by their NMR. spectra.