Oxidative Palladium(II) Catalysis:  A Highly Efficient and Chemoselective Cross-Coupling Method for Carbon−Carbon Bond Formation under Base-Free and Nitrogenous-Ligand Conditions

Abstract

We report herein the development of a general and mild protocol of oxygen-promoted Pd(II) catalysis resulting in the selective cross-couplings of alkenyl- and arylboron compounds with various olefins. Unlike most cross-coupling reactions, this new methodology works well even in the absence of bases, consequently averting undesired homo-couplings. Nitrogen-based ligands including dimethyl-phenanathroline enhance reactivities and offer a highly efficient and stereoselective methodology to overcome challenging substrate limitations. For instance, oxidative palladium(II) catalysis is effective with highly substituted alkenes and cyclic alkenes, which are known to be incompatible with other known catalytic conditions. Most examined reactions progressed smoothly to completion at low temperatures and in short times. These interesting results provide mechanistic insights and utilities for a new paradigm of palladium catalytic cycles without bases.

Highly Diastereoselective C(sp3)C(sp) Cross‐Coupling Reactions between 1,3‐ and 1,4‐Substituted Cyclohexylzinc Reagents and Bromoalkynes through Remote Stereocontrol

“…The N ligands clearly proved to be superior. The commercially available and inexpensive neocuproine [17] (7 b) combined excellent diastereoselectivity with the low formation of regioisomers (< 2 %). PdCl 2 was found to be the best Pd source and switching from Pd to Ni as the catalyst resulted in a deterioration of the d.r.…”

Palladium‐Catalyzed Carbonylations of Arylboronic Acids: Synthesis of Arylcarboxylic Acid Ethyl Esters

“…Initially,t his reactionw as carried out by using 2.0 equivalents of diethylp yrocarbonate (2) [15,19] in the reaction (Table 1, entry 22), and found that the yield was less than the result under an argon atmosphere (Table 1, entry 20). It was also found that the yield was loweri nt he presence of ac ertain amount of water [12] ( Table 1, entry 23).…”

Hoch diastereoselektive C(sp3)‐C(sp)‐Kreuzkupplungen zwischen 1,3‐ und 1,4‐substituierten Cyclohexylzinkreagentien und Bromalkinen

“…4) ersetzt wurde. Die NLiganden erwiesen sich als deutlich überlegen, vor allem Neocuproin [17] (7 b), das kommerziell erhältlich und kostengünstig ist und eine herausragende Diastereoselektivität mit nur geringer Regioisomerenbildung (< 2 %) verbindet. bevorzugten cis-1,3-disubstituierten Cyclohexanderivate [18] mit guten Ausbeuten und hervorragenden Diastereoselektivitäten erhalten (d.r.…”