Abstract
Preparation of symmetrical C2-C2 linked bis-6-bromoindoles and one tris-6-bromoindole containing ether spacers is described. Double regioselective Sonogashira coupling at the C-I bond of benzyl (5-bromo-2-iodophenyl)carbamate with dialkynes allowed preparation of the corresponding bis-benzyl(2-alkynyl-5-bromo)carbamates. Tetrabutylammonium fluoride (TBAF) promoted 5-endo-dig cyclization was successful with substrates derived from alkyldialkynes but failed with substrates derived from aryldialkynes as base catalysis was not sufficient to promote nucleophilic attack on these electron rich alkynes.
Highlights
The indole nucleus is a privileged structure present in a myriad of bioactive compounds many of which have been translated in pharmaceutical leads
The synthesis of the target C2-C2 bisindoles of type 5 was designed in two steps: a regioselective double Sonogashira coupling of arene 215 with dialkynes 3a-i to afford the corresponding coupling products 4a-i followed by 5endo-dig cyclization promoted by fluoride
We have found an efficient protocol for the C-I regioselective consecutive Sonogashira coupling of benzyl (5-bromo-2-iodophenyl)carbamate 2 with aryldialkynes and alkyldialkynes to afford the corresponding bis-alkynes
Summary
The indole nucleus is a privileged structure present in a myriad of bioactive compounds many of which have been translated in pharmaceutical leads.
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