Hydroxyindoles 5,6-dihydroxyindoles

Gronowitz adapted this technology to one-pot syntheses of indole-3-acetic acids and indole-3-pyruvic acid oxime ethers from A-BOC protected o-iodoanilines [328, 329]. Rawal employed the Pd-catalyzed cyclization of A-(o-bromoallyl)anilines to afford 4- and 6-hydroxyindoles, and a 4,6-dihydroxyindole [330], and Yang and co-workers have used a similar cyclization to prepare 8-carbolines 287 and 288 as illustrated by the two examples shown [331]. The apparent extraneous methyl group in 288 is derived from triethylamine. 

A microsomal O -methyltransI erase that methylates a number of alkyl-, methoxy-, and halophenols has been described from rabbit liver and lungs. These methylations are inhibited by SKF-525, A-ethyl-maleimide and /->-chloromercuribenzoate. A hydroxyin-dole O-methyItransferase, which methylates A -acetyl-serotonin to melatonin and, to a lesser extent, other 5-hydroxyindoles and 5,6-dihydroxyindoles, has been described from the pineal gland of mammals, birds, reptiles, amphibians, and fish. 

In the case of pathway (i), it has been argued (91JCS(P2)1941) on the basis of the similarity of the metastable product spectra (with peaks in the 430 nm region) found after the decay of the semiquinones of 5,6-dihydroxyindole 1 and 5-methoxy-6-hydroxyindole 22 (90JPC6666) that the initial product observed after... 

Some 40 years earlier, Harley-Mason and Cromartie synthesized 5-hydroxyindole in excellent yield via the oxidation of 2,5-dihydroxyphenylalanme with potassium ferricyanide (Scheme 6, equation 1) [9]. This simple oxidation when applied to 2,3-dihydroxypheny-lalanine gave 7-hydroxyindole in 20% yield [9] and 3,4-dihydroxyphenylalanine gave 5,6-dihydroxyindole in 30% yield (but not repeatable) [10], This simple oxidation procedure with ferricyanide was used to synthesize bufotenine and serotonin [11], In chemistry related to the Kita indole synthesis, Clive and Stoffman presented a synthesis of 4-halo-5-hydroxyindoles from the corresponding coumarins... 

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