Palladium and iodine approaches to 1,3-dienes, heterocycles and carbocycles

Abstract

A variety of highly-substituted 1,3-dienes and 1,3,5-trienes have been regioand stereoselectively prepared by the palladium-catalyzed coupling of vinylic iodides, internal alkynes and organoboranes in moderate to good yields. The analogous three-component coupling of aryl halides, 1,3-dienes, and boronic acids provides a useful route to 3,6disubstituted cyclohexenes. This method is a very concise and efficient way to synthesize these molecules, whose synthesis has previously required multi-step synthesis. A wide variety of substituted quinolines have been readily synthesized under mild reaction conditions by the 6-endo-dig electrophilic cyclization of iV-(2-alkynyl)anilines by ICI, h, Br% and PhSeBr. The reaction affords 3-halogen-, seleniumand sulfur-containing, and 4-aryl-, alkyland vinylic quinolines in moderate to good yields. Quinolines bearing a hydrogen in the 3-position have been synthesized by the Hg(OTf)2-catalyzed ring closure of these same alkynylanilines. Substituted naphthalenes are readily prepared regioselectively under mild reaction conditions by the 6-endo-dig electrophilic cyclization of appropriate arene-containing propargylic alcohols with ICI, I2, Br2, NBS and PhSeBr. 3-Iodo-2-naphthols have also been prepared in excellent yields by the cyclization of analogous l-aryl-3-alkyn-2-ones. This methodology has been successfully extended to the synthesis of substituted carbazoles and dibenzothiophenes and readily accommodates various functional groups. The electrophile-induced intramolecular z^so-cyclization of 4-methoxyaryl alkynes provides an efficient approach to various 3-halogen-substituted spirotrienones under very mild reaction conditions. Substituted spiro[4.5]trienones, l-azaspiro[4.5]trienones,