Preparation of symmetrical C2-C2-linked bis- and tris-6-bromoindoles by Sonogashira couplings and 5-endo-dig cyclization induced by nBu4NF

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.