Preparation of naphthalenes via Pd-catalyzed annulation of 5-(2-bromophenyl)pent-3-en-1-ynes under Suzuki-Miyaura coupling conditions

Highly substituted naphthalene derivatives were prepared via palladium-catalyzed reaction of 5-(2-bromophenyl)pent-3-en-1-ynes with arylboronic acids. Typically, reaction of 3-bromo-4-(3-(4-chlorophenyl)-5-phenyl-1-(p-tolyl)pent-2-en-4-yn-1-yl)-N-methylaniline (1a) with PhB(OH)₂ in the presence of Pd(PPh₃)₄ as the catalyst under basic conditions provided 8-benzhydryl-7-(4-chlorophenyl)-N-methyl-5-(p-tolyl)naphthalen-2-amine (2a) quantitatively. Overall, 19 new naphthalene compounds were obtained by this methodology and their structures were characterized by spectroscopic methods. In addition, crystal structure of 2j was determined to confirm the structural details. Reaction pathway leading to the desired product is also discussed.