The reaction of 5-bromo-3-(1-methylpyrrolidine)-ylidene-3H-indole with acidic organic compounds
Reaction of 5-bromo-3-(1-methylpyrrolidine)ylidene-3H-indole with methyl iodide or acetic anhydride, followed in each case by base, leads to the formation of 3-keto indoles. The reaction of this ylidene-3H-indole with acidic methylene compounds such as 1-phenylbutane-1,3-dione and malononitrile led to the formation of azepine and carbazole containing systems.
The introduction of an aldehyde function into aromatic and heterocyclic compounds by use of phosphorus oxychloride and methylformanilide or dimethylformamide has been described (1). Smith isolated and characterized the intermediate (1) in the reaction with indole (2).
3-Acylindoles can be obtained from Vilsmeier reaction of indole and tertiary amides in combination with phosphorus oxychloride. However, when 1-methylpyrrolidine-2-one is used as the cyclic amide component, 3-(1-methylpyrrolidin-2-ylidene)-3H-indole (2a) is the product (3).
The structure, reactions and crystallographic analysis of this compound have been discussed (4-8).
We have recently reported the analogous preparation of N-cyclohexylpyrrolidine-ylidene-3H-indole (2b) by the method of Smith, involving the reaction of indole with N-cyclohexylpyrrolidine-2-one in the presence of phosphorus oxychloride (9). The free base could be obtained by very careful neutralization of its hydrochloride salt by NaOH at -5°C.
The 3-(2-pyrrolidineylidene)-3H-indoles are stable compounds and they resist to hydrolysis to the corresponding amino ketones ...