Treatment of beta-keto esters with terminal acetylenes in the presence of a catalytic amount of a manganese complex, MnBr(CO)(5), and molecular sieves, gave multisubstituted aromatic compounds in good to excellent yields. This reaction employs [2 + 2 + 2] cycloaddition of beta-keto esters and 2 equiv of terminal acetylenes with dehydration. In the case of a 1,3-diketone, the corresponding acetophenone derivative and its deacylated compound can be synthesized selectively.
Manganese-Catalyzed Benzene Synthesis by [2+2+2] Coupling of 1,3-Dicarbonyl Compound and Terminal Acetylene
Treatment of a mixture of a 1,3-dicarbonyl compound such as a beta-ketoester or 1,3-ketone and a terminal acetylene with a catalytic amount of MnBr(CO)(5) in heated toluene produces a benzene derivative by a [2+2+2] coupling reaction incorporating the enol part of the dicarbonyl compound and two moles of the acetylene. When the reaction was carried out using phenylacetylene derivatives, the reaction was completely regioselective, producing p-terphenyl compounds in good to excellent yield. Aliphatic terminal acetylenes also reacted readily but gave a mixture of regioisomers. The reaction features high atom economy, neutral conditions, and functional group tolerance, and will be useful for materials-oriented studies.