Rhodium‐Catalyzed Tandem Addition–Cyclization of 1,5‐Enynes with Organoboronic Acids for the Synthesis of Alkylidene‐Cyclobutanes

Abstract

AbstractDescribed here is the rhodium(I)‐catalyzed tandem addition–cyclization of 1,5‐enynes with aryl‐ and alkenylboronic acids. In the presence of triethylamine and catalytic [Rh(OH)(COD)]2 in methanol, both the terminal and internal alkyne substrates possessing an electron‐deficient alkene undergo inter‐ and intramolecular C−C bond formations to yield alkylidene–cyclobutane products. The reaction proceeds through a series of processes involving generation of an aryl or alkenyl rhodium from the organoboronic acid, 1,2‐syn‐carbometalation of the alkyne and 4‐exo‐type‐cyclization of the resulting alkenyl rhodium intermediate with the tethered, carbonyl‐conjugated alkene. Thus, the reaction enables a net R,H‐addition across the 1,5‐enyne π‐system – hydroarylation and hydroalkenylation – under mild rhodium catalysis while achieving 4‐membered ring formation. Preliminary studies show that the reaction can also be rendered enantioselective by employing a chiral diene ligand for the rhodium catalyst.