Pauson–Khand reactions in water

Abstract

We have investigated the cobalt mediated Pauson–Khand (PK) reaction in water. In the presence of detergents and surfactants, Co2(CO)8 and Co4(CO)12 are effective under aqueous-phase, thermal PK reactions. In a water–Triton®X-100 medium, Co4(CO)12 is catalytically active. Further, dicobalthexacarbonyl complexes of alkynes and enynes undergo effective cyclization under thermal (70 °C) and NMO-promoted conditions. The oxidative nature of the latter conditions inhibits the reductive PK reaction. In all protocols, moderate to excellent yields of the cycloadducts are obtained. Substrates that are prone to hydrolysis, such as acetals, highly activated carboxylic acid derivatives, and those bearing propargylic heteroatom groups are tolerated under appropriate conditions. Finally, the more challenging intermolecular cycloadditions can also be easily achieved under aqueous conditions.Key words: alkyne, cycloaddition, green chemistry, Pauson–Khand reaction, water.