Tandem cyclization of alkynes via rhodium alkynyl and alkenylidene catalysis.J Am Chem Soc. 2006 Nov 22; 128(46):14818-9.JA
A rhodium(I)-catalyzed tandem cyclization of alkynes has been developed. The reaction allows for multiple bond formations to occur at both the alpha- and beta-positions of alkynes under mild conditions to yield a variety of fused ring systems as the products. In the presence of triethylamine and the complex derived from [Rh(COD)Cl]2 and P(4-F-C6H4)3, a terminal alkyne is converted to a rhodium alkynyl species which reacts with a tethered alkyl halide at the beta-position to provide a beta,beta-disubstituted alkenylidene complex. The rhodium alkenylidene species then undergoes additional ring closures with a range of pendent functional groups such as alkene, hydroxyl, and phenyl groups through [2 + 2] cycloaddition, nucleophilic addition, and 6pi-electrocyclization processes, respectively.