Oxidant-Dependent Chemoselectivity in the Gold-Catalyzed Oxidative Cyclizations of 3,4,6,6-Tetrasubstituted 3,5-Dien-1-ynes

Abstract

A distinct chemoselectivity in the gold-catalyzed oxidative cyclization of 3,5-dien-1-ynes was observed when 3,5-dichloropyridine <i>N</i>-oxide replaced 8-methylquinoline <i>N</i>-oxide as the oxidant; the resulting cyclopentadienyl aldehydes were obtained in good yields. The altered chemoselectivity is attributed to a prior enyne cyclization in the presence of 3,5-dichloropyridine <i>N</i>-oxides. The use of <i>N</i>-iminopyridium ylide enables a similar iminocyclization reaction to give cyclopentadienyl imines efficiently. Our experimental data support a prior gold-catalyzed cyclization of 3,5-dien-1-ynes to form gold carbene, followed by the oxidation with <i>N</i>-oxide