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Indoles - Sundberg R.J.

Sundberg R.J. Indoles - Academic press, 1996. - 95 p.
ISBN 0-12-676945-1
Download (direct link): indoles1996.djvu
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As is broadly true for aromatic compounds, the a- or benzylic position of alkyl substituents exhibits special reactivity. This includes susceptibility to radical reactions, because of the stabilization provided the radical intermediates. In indole derivatives, the reactivity of a-substituents towards nucleophilic substitution is greatly enhanced by participation of the indole nitrogen. This effect is strongest at C3, but is also present at C2 and to some extent in the carbocyclic ring. The effect is enhanced by N-deprotonation.
Nu -
“ 1 * -■ i
This reactivity pattern underlies a group of important synthetic methods in which an a-substituent is displaced by a nucleophile by an elimination-addition mechanism. Even substituents which are normally poor leaving groups, such as alkoxy and dialkylamino, are readily displaced in the indole series.
The material in the succeeding chapters describes both the synthesis of the indole ring and means of substituent modification which are especially important in indole chemistry. The first seven chapters describe the preparation of indoles from benzenoid precursors. Chapter 8 describes preparation of indoles from pyrroles by annelation reactions. These syntheses can be categorized by using the concept of bond disconnection to specify the bond(s) formed in the synthesis. The categories are indicated by the number and identity of the bond(s) formed. This classification is given in Scheme 1.1.
Chapters 9, 10 and 11 describe methods for substitution directly on the ring with successive attention to N1, C2 and C3. Chapters 12 and 13 are devoted to substituent modification as C3. Chapter 12 is a general discussion of these methods, while Chapter 13 covers the important special cases of the synthesis of 2-aminoethyl (tryptaminc) and 2-aminopropanoic acid (tryptophan) side-chains. Chapter 14 deals with methods for effecting carbocyclic substitution. Chapter 15 describes synthetically important oxidation and reduction reactions which are characteristic of indoles. Chapter 16 illustrates methods for elaboration of indoles via cycloaddition reactions.
As for the other volumes in this series, examples of synthetic procedures have been given. These have been choscn to indicate the basic operations involved
in the individual syntheses. The procedures have been adapted from the published procedures for a succinct style of presentation. The original reference should be consulted for details which may not have been included.
There are a number of other sources of information available about the synthesis of indoles. The most comprehensive entree to the older literature is through Volume 25, Parts I—III, of The Chemistry of Heterocyclic Compounds, which were published between 1972 and 1979[23], Work to the early 1980s is reviewed in Comprehensive Heterocyclic Chemistryl24] and a second edition is forthcoming[25]. Other reviews emphasizing recent developments are also availablc[26-28].
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