The asymmetric unit of the title compound, C13H14N2·1.5H2O, contains two similar molecules of 3-(1-methylpyrrolidin-2-ylidene)-3H-indole, (I), and three water molecules. (I) is the product of reacting indole with 1-methylpyrrolidin-2-one in the presence of phosphorus oxychloride. Both organic molecules are almost completely planar; the maximum distances above and below the least-squares plane through all the atoms of molecule 1 are 0.050 (8) and −0.045 (8) Å, respectively, and the deviations for molecule 2 are 0.096 (8) and −0.059 (8) Å, respectively. In the crystal, the two crystallographically different molecules alternate in π-stacked columns [centroid–centroid distances = 3.729 (5) and 3.858 (5) Å], which are linked by O—H⋯N hydrogen bonds to a network of hydrogen-bonded water molecules. O—H⋯O interactions are also present.
In the title compound, C18H19BrN2O, the seven-membered azepine ring adopts a twist-boat conformation: the bond angles about the azepine N atom are indicative of sp
2 hybridization. The dihedral angle between the plane of the carbon–carbon double bond of the enone unit and the mean plane of the indole ring is 27.8 (1)°. In the crystal, an N—H⋯O hydrogen bond links the molecules into chains along the b axis.
The reaction of indole with the complex formed from 1,3-dimethylimidazolidin-2-one or N-methyloxindole with phosphorus oxychloride (phosphoryl chloride), was studied. In similar reactions of five-membered tertiary amide rings, 3-(1-alkyl-pyrrolidin-2-ylidene)-3H-indoles or ring opening products were obtained but in these cases, new products N 1 ,N 2 -dimethyl-N 1 -[tri-(1H-indol-3-yl)methyl]ethane-1,2-diamine and N-methyl-2-(3,3,3-tri-(1H-indol-3-yl)propyl)aniline as trimers of indole were obtained.
Vilsmeier-Haack reaction also called Vilsmeier reaction was first used for the formylation of an active arene, during which a mixture of phosphorus oxychloride and dimethylformamide (Vilsmeier reagent) was added to N,N-dimethyl aniline [1].The reaction of indole with the Vilsmeier reagent, followed by base, is the classic and very efficient method for the 3-formylation of indoles (Scheme 1) [2]. Before the alkaline hydrolysis step, the product which was a salt, 3-[(dimethylamino)methylene]-3Hindolium chloride (1), was followed by a basic workup affording dimethylamine and aldehyde. 3-Acylindoles can be obtained from Vilsmeier reaction of indole and tertiary amides in combination to phosphorus oxychloride [3]. Scheme 1.The reaction of indole with Vilsmeier reagent for the 3-formylation of indoles
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