Synthesis of Bulky Phosphines by Rhodium-Catalyzed Formal [2 + 2 + 2] Cycloaddition Reactions of Tethered Diynes with 1-Alkynylphosphine Sulfides

摘要

In the modern organic synthesis, bulky phosphine ligands play an indispensable role in preparing biologically interesting compounds as well as organic functional materials. Synthesis of such bulky ligands is hence quite important. However, the methods for the synthesis are mostly limited to the reaction of a chlorophosphine with a bulky organometallic reagent and the transition-metal-catalyzed phosphination or phosphinylation of a bulky aryl halide. We have been focusing on 1-alkynylphosphines as precursors of new phosphines. In the course of our study on the use of 1-alkynylphosphines, we report herein a conceptually different approach to bulky phosphines. Rhodium-catalyzed formal [2 + 2 + 2] cycloaddition reaction of 1,6-diynes and 1-alkynylphosphine sulfides afforded benzene rings having a thiophosphinyl moiety. When substrates are properly designed, the newly formed benzene rings naturally have one or two substituents next to the thiophosphinyl group, which provide sterically congested environment around the phosphorus.