Smith, G. F., The Acid-Catalyzed

Smith, G. F., The Acid-Catalyzed Polymerization of Pyrroles and Indoles, 2,287. 

Indole forms a dimer and a trimer under various acidic conditions. The dimer is formed by electrophilic attack on indole by the 3-protonated species. The structure of the trimer, first proposed by G. F. Smith [15], was proven by synthesis [16]. Trimer results from acid-catalyzed opening of the indoline ring in the dimer, followed by electrophilic attack on a second indole. The dimerization-trimerization process is evidently reversible in 0.5 M H2SO4. A composition of approximately 1 0.4 0.3 is reached from the indole, the dimer or the trimer [17]. An isomeric trimer 5-C can be... 

Light metal alkoxides, e. g. Mg- and Al-alkoxides, catalyze the reaction between Mg and many organic halides, making the use of ethers unnecessary. Mg-alkoxide is conveniently prepared in situ, on warming with a trace of iodine.— E Mg-powder stirred and refluxed under Ng with excess chlorobenzene and some isopropanol in the presence of a trace of iodine to initiate the reaction, then treated with COg benzoic acid. Y 90%.—Fresh Mg-powder gives better yields than the usual turnings. In place of excess halide, a hydrocarbon medium, e. g. toluene, methylcyclohexane, or kerosene can be used. F. e. s. E. T. Blues and D. Bryce-Smith, Chem. Ind. 1960, 1533. 

---