Indolenines acid-catalyzed rearrangement

The derived quaternary salts (e.g. 201) give anhydro compounds (e.g. 202) on treatment with alkali. (3-Pentamethylpyrrolenine (2,3,3,4,5-pentamethylpyrrole) undergoes quantitative conversion to the a-isomer (2,2,3,4,5-pentamethylpyrrole) either on heating (>200°C) or in 1M HC1 at room temperature (71CC1093). Indolenines also undergoes an acid-catalyzed rearrangement (e.g. 203 — 204), known as the Plancher rearrangement. 

Polyalkylated 2- and 3-pyrrolenines (2H- and 3H-pyrroles) and 3-indolenines (3H-indoles) are formed by methylation of the parent 1H heterocycles (see Section 3.05.1.2.7), but the acid-catalyzed or thermal rearrangement of 2,2,5-trisubstituted 2H-pyrroles and of 3,3-disubstituted 3//-indoles yields the corresponding 2,3,5-trisubstituted IH-pyrroles and the 2,3-disubstituted l//-indoles, respectively (see Section 3.05.1.1). 

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