| Description |
During the past few decades, one-pot multicomponent reactions have attracted significant attention because of their ability to install multiple carbon-carbon or carbonheteroatom bonds in a single step. However, the development of these reactions is a challenge because of the generation of many side products arising from undesired reaction pathways. Hence, optimization for the formation of desired products is difficult. Our group has been involved in developing such multicomponent reactions that take advantage of the stability of π-allyl/benzyl palladium species to generate biologically relevant and synthetically challenging products in an efficient manner. Herein, I describe the development of three novel multicomponent transformations to achieve difunctionalization of cheap olefins such as ethylene and dienes. First, a Pd(II)-catalyzed three-component coupling involving ethylene, alkenyl triflates, and aryl boronic acids is described, where 1,1-vinylarylated products can be obtained in high yields and good to high selectivity. The crucial factor for an efficient reaction is cationic Pd(II)-intermediates, which prevent side products such as Suzuki products and Heck products. In general, the scope of the reaction is good as both electronrich and electron-withdrawing boronic acids are tolerated. Heteroaromatic cross-coupling partners are also compatible under the reaction conditions. However, the scope is limited to six-membered alkenyl electrophiles, which bias the selectivity towards the formation of 1,1-vinylarylated products. Second, the scope of this three-component reaction was extended to aryl electrophiles such as aryl diazonium salts. The reaction can also be used to couple allylic carbonates as the olefin source instead of ethylene to afford a wider range of 1,1-diarylalkanes. Also, deuterium labeling study and cross-over experiment revealed useful information regarding the mechanistic aspect of the reaction. Finally, 1,2-hydrovinylation of terminal 1,3-dienes was achieved with alkenyl triflates/nonaflates and a hydride source. The reaction can be used to couple a variety of triflates derived from natural products to generate complex molecules in a mild fashion. Additionally, configurationally-defined alkenyl triflates (i.e., E/Z) can be coupled efficiently to generate synthetically useful tri- and tetrasubstituted alkenes. |
