Pyrrolidine → 6-phenyl-1H-indole

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Reaction Steps

A mixture of 4-phenyl-2-nitrotoluene (1.8 g, 8.5 mmol), N,N-dimethylformamide dimethyl acetal (4.4 ml, 33 mmol) and pyrrolidine (0.78 ml, 9.3 mmol) was heated in DMF (20 ml) at 110° C. for 16 hours. The resulting deep red solution was poured into water (100 ml) and extracted with ether (2×100 ml). These extracts were concentrated to give a deep red oil which was dissolved in acetone (5 ml) and then added to a mixture of titanium(III) chloride (40.4 g of a 20% solution in aqueous hydrochloric acid, 52 mmol) and ammonium acetate (80 ml of a 3.9M aqueous solution). The resulting mixture was shaken for 10 minutes and then extracted with ether (3×100 ml). The extracts were washed with brine, dried and concentrated to give a dark solid, which was crystallised from a mixture of petrol (60°-80° C.) and dichloromethane to give 6-phenylindole (1.16 g, 71% yield) as a dark crystalline solid melting at 154° C. (Literature m.p. 160°-1° C., O.Sus et al, Justus Liebigs Ann. Chem., 1955, 593, 91).

Provenance & Evidence