[Cu]-catalyzed domino Sonogashira coupling followed by intramolecular 5-exo-dig cyclization: synthesis of 1,3-dihydro-2-benzofurans.

An efficient [Cu]-catalyzed domino Sonogashira coupling of o-bromobenzyl tertiary alcohols with terminal aryl acetylenes followed by an intramolecular anti-5-exo-dig cyclization is presented. The terminal aryl acetylenes were identified as ideal coupling partners that permit in situ intramolecular oxacyclization by the hydroxyl group as a pre-existing nucleophile of the alcohol. Notably, the intramolecular nucleophilic attack of the hydroxyl group took place on the alkyne moiety in a highly regio- and stereoselective manner. Interestingly, this method was amenable to a wide variety of o-bromobenzyl tertiary alcohols and furnished the corresponding cyclic ethers. On the other hand, when terminal alkyl acetylenes were used as the coupling partners, the reaction was impeded after the Sonogashira coupling.