Important reactions of indoles schematic

Acid catalysed equilibration of certain yohimbane derivatives at C-3 is mediated by one or more of the following equilibria the driving force being toward the direction of greater thermodynamic stability. 

Autooxidation products and their transformation products are well known for Type II and III alkaloids. For Type I alkaloids autodxidation usually produces dehydro- and tetradehydro-compounds when the lone pair electrons of the basic nitrogen can play the part of Y in the transformations of Chart 3.5. 

It is known that autooxidation of 2,3-diethylindole or 2,3-hexamethyleneindole can yield the corresponding 2-acylindole, a system which has been recognized recently in a number of natural products. The exact mechanism of the reaction is not yet known but following Chart 3.5, the route below seems reasonable (see also p. 66). 

Indoline alkaloids have not been mentioned here because the key which unlocks their nuclei for degradative or interconversion work is the oxidant which converts them to the corresponding indolenine. From a biochemical point of view such an oxidation is probably the reversal of a reduction step which in essence had served to stabilize the molecule. The resultant indolenines are usually highly reactive, see for example decomposition of akuam-micine Chart 3.2 and the unfolding of the hexacyclic ajmaline molecule to a tricyclic derivative (Chapter VIII). 

Under this heading are discussed representative alkaloids derived from tryptophan equivalents in the following ways, modification of the side chain, alkylation, ring closure, dimerization and combination with mevalonic acid. A number of these bases presented no structural problem once they were analysed and recognized to contain an indolic nucleus. Others although simple contained novel elements which were not always immediately appreciated at the time of their first isolation and study. Many of these alkaloids are active principles of plants long used as drugs by native populations. 

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