Ethynylation of indoles with 1-benzoyl-2-bromoacetylene on Al2O3

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

“…Bis(1-vinyl)-2,2'-(1,4-phenylenepyrrole) 47 is protonated by a superbasic acid to the unsymmetrical dication 48 -with α-and β-protonated pyrrole rings [205]. [206][207][208][209][210][211][212][213][214][215]. On the surface of SiO 2 the reaction of pyrrole and 2-phenylpyrrole with 2-acyl-1-phenylacetylenes takes place stereo-and regioselectively with the formation of (Z)-2-ethenylpyrroles 49 [206], whereas the N-adducts 50 are formed in the KOH/DMSO system [207].…”

“…Cross-coupling of NH-pyrroles with haloacetylenes on Al 2 O 3 leads to 2-ethynylpyrroles 51 [208][209][210]. N-Vinylpyrroles, tetrahydroindoles, and indoles were used successfully in this reaction [211][212][213]. It was established for the first time that the oxides of Ca, Mg, Zn, and Ba promote the ethynylation of 2-phenylpyrrole by bromobenzoylacetylene, and ZnO and BaO are more active than Al 2 O 3 [214].…”

Organic Solid-State Reactions

“…The intramolecular solid-state substitution of the aryl-thiodienolether in Scheme 24 to give the naphthalene derivative requires oxidation with solid iodine or its vapor [190]. The ethinylation of the 1H-benz[g]indole by grinding with solid 1-benzoyl-2-bromoacetylene in the presence of Al 2 O 3 yields both the 3-and 2-substitution in about equal amounts [191]. Furthermore, the now easily available elusive solid N-aryl-methylene-iminium chlorides (from haxahydro-1,3,5-triazines and gaseous HCl, see Scheme 28) are potent reagents for arylaminomethylations.…”

Cross-coupling of 4,5,6,7-tetrahydroindole with functionalized haloacetylenes on active surfaces of metal oxides and salts

“…We recently developed a new method of introduction of an acetylene substituent into the position 2 of the pyrrole ring [14,15] or the position 3 of the indole ring [16,17] based on the cross-coupling of pyrroles or indoles with electrophilic haloacetylenes on the surface of aluminum oxide that did not require special catalysts, bases, solvents, inert atmosphere, and which proceeded at room temperature. The most promising for the use in this reaction is the 4,5,6,7-tetrahydroindole that has become the most available indole derivative due to the development of the one-pot technology of its preparation from cyclohexanone oxime and acetylene [18].…”

“…However taking into account the fundamental difference in the reactivity of the 2-phenylpyrrole and the 4,5,6,7-tetrahydroindole in some reactions [22,23] and also the unlike reactivity of the benzoylbromoacetylene and the ethyl bromopropynoate in the reaction of the ethynylation of the pyrrole [14,20] and indole [16,17] rings it was diffi cult to predict in advance which of the cited active surfaces would be the most suitable for the synthesis of 2-benzoylethynyl-or 2-ethoxycarbonylethynyl-4,5,6,7-tetrahydroindoles.…”