Functionalized α-keto stabilized sulfonium ylides as highly active ligand precursors for palladium catalyzed Suzuki–Miyaura cross-couplings

Abstract

Five α-keto stabilized sulfonium ylides as type (Me)2SCHC(O)C6H4-p-X (X=H, Br, NO2, CH3 and OCH3) {L1–L5} were used as ligand precursors in the Suzuki–Miyaura cross-coupling reaction. The best catalytic performance was obtained by using a sulfonium ylide/Pd ratio of 2:1. The catalytic systems displayed high activities, which increased in the order R=NO2 (L3)<Br (L2)<H (L1)<CH3 (L4)<OCH3 (L5). The coupling reactions proceeded smoothly with 0.05mol% PdCl2 and 0.1mol% L5 in DMF at 130°C between varieties of electronically activated, deactivated and neutral aryl halides and aryl boronic acids within short reaction times and without the need for exclusion of air which gave good to high yields of the corresponding products. All the studied ligands demonstrated very high activity in the Suzuki–Miyaura cross-coupling, which yielded turnover numbers up to 1940. Comparative studies showed that the performance of sulfonium ylide L5 is significantly superior to that of related phosphine-free ligands.