Heck Coupling with Nonactivated Alkenyl Tosylates and Phosphates

Angewandte Chemie International Edition Volume 45, Issue 20, Pages 3349-3353

Considerable efforts have been undertaken by numerous groups in academia and industry over the past decade to expand the repertoire of coupling reagents in palladium(0)-catalyzed cross-coupling reactions.[1] In particular, alkenyl phosphates and tosylates have proven their worth in various cross-coupling reactions, such as the Stille,[2] Suzuki,[2e],[f], [3] Negishi,[2b] Kumada,[2b], [3e], [4] Sonogashira,[2b],[e],[f], [5] Buchwald-Hartwig,[4a], [6] carbonyl enolate,[3d] and Heck couplings,[7] as effective alternatives to the less stable and typically more expensive alkenyl triflates and nonaflates.[8] However, the majority of this work has focused on the use of activated vinyl phosphates and tosylates, such as ,-unsaturated systems or -heteroatom-substituted alkenes, for which the oxidative-addition step is nonproblematic with palladium(0) catalysts bearing aryl phosphine ligands. Less attention has been devoted to nonactivated counterparts, most likely because of the greater difficulty in carrying out the first step of the catalytic cycle, namely the oxidative addition.[3d], [4], [5], [9]

We now report on catalyst systems composed of a palladium complex with a basic, hindered alkyl phosphine that can promote the Heck coupling of nonactivated vinyl tosylates and phosphates with electron-deficient alkenes in good yields, thereby increasing the scope of this important cross-coupling reaction. Furthermore, during these studies we observed an interesting 1,2-isomerization with certain alkenyl tosylates and phosphates under reaction conditions that provide coupling yields as high as 95 %