Synthesis 



of the Fischer ring-closure to the phenyl-hydrazone of a-keto- 

 suberic acid and the subsequent ehmination of carbon dioxide 

 from the resuhing dibasic acid (5-3-(2-carboxy)-indolyl- 

 valeric acid). This synthesis was strictly analogous to that of 

 the two lower homologues (Jackson and Manske (1930); 

 Manske and Robinson (1927) ), the phenyl-hydrazone being 

 obtained by means of the Japp-Klingemann^ reaction from 

 the homologous ethyl cyclo-heptanone carboxylate. This was 

 prepared following the method first used by Kotz and Michels 

 (1906) for the synthesis of ethyl cyclo-hexanone carboxylate. 

 For the 1936 paper, cyclo-heptanone (suberone) was obtained 

 by the procedure (described as "excellent" by Manske and 

 Leitch) due to Mosettig and Burger (1930). 



In outlining the preparation of the 6^- methyl indolyl deriva- 

 tive, Manske and Leitch wrote that "the now well-known 

 procedure, starting with /)-toluidine in this case and ethyl 

 cyclo-pentanone carboxylate, was employed". 



A number of other indole derivatives, mainly of purely 

 chemical interest at present, have been prepared by Manske 

 (1930), including the phenyl ether of tryptophol mentioned 

 above. The "recently much exploited" reaction of Japp and 

 Klingemann was used in all cases to prepare the requisite 

 phenyl-hydrazones. Manske also referred to the synthesis by 

 Barrett, Perkin, and Robinson (1929) of 5- and 6-methoxy-p 

 (3-indolyl)-propionic acids by methods analogous to those of 

 Manske and Robinson (1927). Manske himself (loc. cit.) 

 synthetized the 7-methoxy-3-indolyl-propionic acid and a 

 more complex 62:-substituted indolyl-propionate. 



An isomeric form of indole has been reported by Braun 

 and Nelles (1937), but it is not known how it or its compounds 

 affect plant growth. 



Other Compounds 



For preparation and properties of indole-carboxylic acids, 

 see the textbooks. The 3-carboxy compound is easily con- 

 verted into indole. 



* The Japp- Klingemann (1888) reaction arises from the addition of 

 benzene-diazonium chloride in ethyl alcohol made alkaline with KOH. 



109 



