Solvent effects in copper(I)-mediated 5-endo cyclisation of secondary bromo-enamides

Abstract

Secondary bromoenamides 5, 14-18, 32 and 33 undergo efficient 5-endo cyclisation reactions to give α,β-unsaturated monoene lactams 9, 19–23, 34 and 35 under atom transfer conditions mediated by CuBr and the tripyridylamine 6 in refluxing toluene (59–87%). Changing the solvent to refluxing 1,2-dichloroethane furnishes α,β-unsaturated diene lactams 26-31, 36, and 37 instead (42–86%).