The preparation of aromatic aldehydes by the use of N-methylformanilide and phosphorus oxychloride was first accomplished by Vilsmeier and Haack (1) who used this method for the synthesis of p-alkylaminobenzaldehydes. In a series of patents, Kaliseher, Scheyer, and Keller (2) reported that the reaction is applicable to certain phenolic ethers and aromatic hydrocarbons, and these claims were verified by Wood and Bost (3). Application of the reaction to indole derivatives unsubstituted in the 3-position was made by Wolff and Werner (4) who prepared 2-phenylindole-3-aldehyde, l-methyl-2-phenylindole-3-aldehyde, and others. The preparation of 2-phenylindole-3-aldehyde by the method of Wolff and Werner has been repeated; consistently high yields (90%) were obtained.In uder to establish the structure of 2-phenylindole-3-aldehyde with greater certainty, it was prepared from 2-phenylindole by the use of the Reimer-Tiemann reagents, chloroform and potassium hydroxide. The modification employed
The Pfitzinger2 method of synthesis of substituted cinchoninic acids, like cinchophen, from isatin and methyl ketones with concentrated potash, serves as a convenient reaction when no alkali-sensitive groups are present. The desirability of a more gentle method suggested the Knoevenagel8 catalysts in place of the alkali.When an alcoholic solution of isatin and acetophenone containing a small quantity of diethylamine is allowed to stand overnight a copious yield of a product (I) is obtained. The product is not cinchophen but is, according to its empirical formula, an addition product C8H502N
Recent interest in the chemistry of Mannich bases derivable from indole (1,2) and its derivatives (3, 4) prompts us to report on work done in this field some years ago. At that time it was deemed desirable to add the indole nucleus to the list of basically substituted heterocyclic systems under investigation as
Condensations of Isatin with Acetone by the Knoevenagel
Method1By F. Braude with H. G. LindwallIn a recent article it was shown2 that isatin and acetophenone will condense, in the presence of certain bases, to yield 3-hydroxy-3-phenacyloxindole. This reaction suggested the use of other methyl ketones like acetone. Isatin and acetone condense when present with small amounts of diethylamine to yield 3-acetonyl-3-hydroxyoxindole (I).The condensation involves the /3-carbonyl of the isatin molecule rather than the nitrogen, for N-methylisatin will also react with acetone to yield a product with chemical properties similar to those of (I).Compound (I) decomposes upon the application of heat, or upon being New York, N. Y.
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