Synthesis of ‘Spacer'-Naproxen [2-(6-Methoxybiphenylen-2-yl)propanoic Acid] and -Isonaproxen [2-(7-Methoxybiphenylen-2-yl)propanoic Acid

Abstract

The CpCo(CO)2-catalyzed cocyclization of 1,2-diethynyl-4-methoxybenzene with alkynes can be applied to the synthesis of ‘spacer’-naproxen [2-(6-methoxybiphenylen-2-yl)propanoic acid] and its 7-methoxy isomer, ‘spacer’-isonaproxen. While unsymmetrical alkynes are incorporated without regioselectivity, the methoxy group in 6-methoxy-2,3-bis(trimethylsilyl)biphenylene directs electrophiles to C-3, thus allowing for regiochemical differentiation between the 2- and 3-positions.