Indole Ehrlich color reaction

By using an aromatic aldehyde carrying an electron-releasing group the intermediate cation can be stabilized. This is the basis of the classical Ehrlich color reaction for pyrroles, indoles and furans which have a free reactive nuclear position (Scheme 19). As expected, pyrroles react preferentially in the exposition and indoles in the (3-position, but if these positions are filled, reaction can occur at other... 

The indoles 38 and 39 give a negative Ehrlich color reaction, indicating substitution at position 2 and 3 of the indole ring. The mass spectra of these compounds show a base peak at m/z 198, C,4H,6N, which originated via cleavage of the C-8-C-9 bond. On the basis of spectral data, 38 seemed to be identical to deoxybrevianamide E which had been obtained by Birch and Wright (72) upon treatment of brevianamide E (44) with Zn and AcOH. Later, 38 and 44 were... 

It can be concluded from the publications of Rohde [2] and Freund and Lebach [3, 4] that it was Ehrlich who first suggested the use of 4-(dimethylamino)-benzalde-hyde in the presence of hydrochloric acid for color reactions with methylketols that was found also to apply to indole derivatives [S]. Auterhoff [6] designated a reagent for urobilinogen, consisting of a solution of 2 g 4-(dimethylamino)-benzaldehyde in 20 percent hydrochloric acid, correctly as Ehrlich s solution. Hence, it is essentially correct to refer to all reagents which contmn these components as Ehrlich s reagent. 

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