An Electron‐Deficient Diene as Ligand for Palladium‐Catalyzed Cross‐Coupling Reactions: An Efficient Alkylation of Aryl Iodides by Primary and Secondary Alkylzinc Reagents

Abstract

An electron-deficient diene, L 1 , was found to be an effective ligand in facilitating palladium-catalyzed Negishi couplings involving primary and secondary alkylzinc reagents. The reactions took place readily at 60 8C in THF with 5 mol% of a catalyst generated in situ from bis(acetonitrile)palladium di-and L 1 , and functional groups such as chloro, bromo, etc. attached to phenyl ring as well as b-H atoms adjacent to the reaction site were well tolerated. The problematic isomerizations in secondary alkyzinc reagents involved in the reactions reported in the literature were also observed in our system when isopropylzinc chloride was employed alone as the nucleophile. However, the isomerization was significantly suppressed when i-Pr 2 Zn was utilized in the presence of L 1 .

Palladium‐Catalyzed Bromoalkynylation of CC Double Bonds: Ring‐Structure‐Dependent Synthesis of 7‐Alkynyl Norbornanes and Cyclobutenyl Halides

“…[3] In addition, their strained structure and high potential to coordinate to transition metals, as well as their possible industrial applications have attracted considerable research interest. [4] Thus, we decided to react phenylethynyl bromide (2 a) with norbornene (1 a), expecting to obtain 2-bromo-3-(2-phenylethynyl)bicyclo[2.2.1]heptane (3 aa; Scheme 1). However, when using the previously optimized conditions, [2] we did not detect the formation of 3 aa, instead we obtained 2-bromo-7-(2-phenylethynyl)-bicyclo[2.2.1]heptane (3 a) in excellent yield, as confirmed by 1 H NMR spectroscopy.…”

Aerobic Heterogeneous Palladium-Catalyzed Oxidative Allenic C−H Arylation: Benzoquinone as a Direct Redox Mediator between O 2 and Pd

“…In addition, other electron-deficient alkene ligands that cannot act as ETMs or oxidize Pd(0), but may promote reductive elimination, were investigated in the aerobic oxidation (Scheme 5b). [60][61][62][63] Maleic anhydride (L 1 ), dialkyl fumarates (L 2 and L 3 ), and dibenzylideneacetone (dba, L 4 ) were thus added in place of DMBQ, but in all cases only trace amounts (<2%) of product 3aa were detected. b This observation further verifies the bifunctional role of DMBQ.…”

Carbon–Carbon Bond Forming Reactions Mediated by Organozinc Reagents

“…Another way by which reductive elimination can be facilitated, and thereby competitive β-hydride elimination can be outscored, is by using π-acceptor ligands. For instance, the electron-deficient diene ligand 340 in combination with PdCl 2 (MeCN) 2 catalyzes the reaction of secondary cycloalkylzinc halides (as well as primary alkylzincs) with aryl iodides (Scheme 4.78) [247]. High yields are obtained and only minor amounts of reduction by-products are observed.…”