Raney nickel indoles

Gassman and co-workers developed a synthetic route from anilines to indoles and oxindoles which involves [2.3]-sigmatropic rearrangement of anilinosul-fonium ylides. These can be prepared from Ai-chloroanilines and ot-thiomcthyl-ketones or from an aniline and a chlorosulfonium salt[l]. The latter sequence is preferable for anilines with ER substituents. Rearrangement and cyclizalion occurs on treatment of the anilinosulfonium salts with EtjN. The initial cyclization product is a 3-(methylthio)indole and these can be desulfurized with Raney nickel. Use of 2-(methylthio)acetaldehyde generates 2,3-unsubstituled indoles after desulfurization[2]. Treatment of 3-methylthioindoles with tri-fiuoroacetic acid/thiosalieylie acid is a possible alternative to Raney nickel for desulfurization[3]. 

The Gassman indole synthesis involves an one-pot process in which hypohalite, a P-carbonyl sulfide derivative 2, and a base are added sequentially to an aniline or a substituted aniline 1 to provide 3-thioalkoxyindoles 3. Raney nickel-mediated desulfurization of 3 then produces the parent indole... 

In 1974, Gassman et al. reported a general method for the synthesis of indoles. For example, aniline 5 was reacted sequentially with r-BuOCl, methylthio-2-propanone 6 and triethylamine to yield methylthioindole 7 in 69% yield. The Raney-nickel mediated desulfurization of 7 then provided 2-methylindole 8 in 79% yield. The scope and mechanism of the process were discussed in the same report by Gassman and coworkers as well. 

A number of pentacyclic quaternary j8-carbolinium derivatives undergo reactions in which the hetero ring is cleaved. Thus semper-virine (286) is converted in poor yield into the indole derivative 287 on catalytic hydrogenolysis with Raney nickel. Alstonine and serpentine yield the analogous product on treatment with selenium. 

We chose the microwave-enhanced Raney Nickel catalyzed hydrogen isotope exchange of indole and N-methylindole as our substrates and D20, CD3COCD3, CD3OD and CDC13 as the solvents. The thermal reaction had already been the subject of a recent study [44], The microwave-enhanced method was some 500-fold faster than the corresponding thermal reaction (at 40 °C). Furthermore the pattern of labeling (Scheme 13.3) varied with the choice of solvent. Thus in the case of indole it-... 

An alternative synthesis from the Glaxo patents involves Fnedel-Crafts acylation of the 3-position of the indole intermediate 22 (Scheme 5) Reaction of hydrazine 10 with (phenylthio)acetaldehyde gave hydrazone 20, which was subjected to the Fischer indole reaction to give 3-thiophenylindole 21. It is noteworthy that this Fischer cyclization took place at room temperature because most require heat. Reductive desulfurization of 21 using Raney nickel provided indole 22. Acylation of the 3-position... 

As indicated in Scheme 27, indoles may be alkylated by their acid-catalyzed reaction with alcohols. Similarly, r-butylation of pyrroles has been effected by the acid-catalyzed reaction with t- butyl acetate (B-77MI30502), and the diarylmethylation of 1-methylpyrrole from the acid-catalyzed reaction with the chromium trichloride complex of the diarylcarbinol has been described (78JA4124). The alkylation of indoles by alcohols in the presence of the aluminum alkoxide and Raney nickel appears to be efficient for the synthesis of 3-substituted indoles, but is less successful in the alkylation of 2-methylindole (79JHC501). The corresponding isopropylation of pyrrole produces 2,5-diisopropylpyrrole and 1-isopropylpyrrolidine, as the major products (79JHC501). 

Preferential hydrogenation of the heterocyclic ring of N- and C-arylpyrroles and of indoles and isoindoles is usual, but hydrogenation over Raney nickel can also lead to the... 

Catalytic reduction of the C-alkenyl and -alkynyl substituents over palladium or Raney nickel can be effected without concomitant hydrogenation of the heterocyclic system to give the corresponding alkyl-pyrroles and -indoles (72HC(25-2)65, B-77MI30504). 

A 2.42 g (0.01 mole) of ethyl N-(p-cyanoethyl)indole-2-carboxylate is suspended in acetic anhydride (20 ml). The suspended compound is hydrogenated on a Parr shaker in the presence of Raney nickel. The uptake of hydrogen is complete after 1.5 h. The product recovered is recrystallized from benzene-hexane. The product obtained is ethyl l-(3-acetamidopropyl)indole-2-carboxylate, melting point 83.5°-84.5°C. 

To a solution of N-methyl-3-(phenylthio)-lH-indole-5-methanesulphonamide (460 mg) in absolute ethanol (50 ml) was added Raney nickel [4.6 g, 50% slurry in water, washed to neutrality with deionized water (60 ml)] and the reaction mixture refluxed for 16 h under an atmosphere of nitrogen. On... 

M) + pyrrolidine gave a mixture (10 1) of pyrrolidine enamine, mp lOB-1100 (MeOH), and H.N-dimethylenamine (5 hr reflux, 97% yield) which, on reduction (Raney nickel-hydrazine), gave the indole (93% yield). 

Metayer (97) has alkylated, over Raney nickel, such nitrogen compounds as indole and N-formyl-l-phenethylamine. For a Raney nickel catalyzed acylation of an amine, see Blout and Silverman (57), who obtained hydrocarbostyril when the hydrogenation of o-nitrocinnamic esters was continued after three equivalents of hydrogen had been taken up. 

---