Versatile Reactivity and Catalytic Effects of Copper(II) Halides in Organic Syntheses

Abstract

Copper(II) salts are widely applied for the halogenation of aromatic and heteroaromatic systems, the halides. In coupling reactions, CuCl 2 has been used as a catalyst for the benzylation of aromates, the synthesis of alkanes, and the preparation of diacetylenes, cyclohexenones and symmetric biaryls. It has further proved suitable for stereoselective cyclization to lactones, carbon-nitrogen coupling and lactamization, and for the simple preparation of aroylaminohydrazones, the allylic amination of olefins, the carbonylation of alkylamines, and heterocyclizations to pyrrolidinones, pyridinones, pyrroles and dihydrofurans. The dehydrogenation of carbocycles and heterocycles can be used in the synthesis of gibberelic acid, for the aromatization of oestrogen derivatives and for the conversion of dihydrouracils to uracils. From tetrahydroisoquinolines, dihydro derivatives have been formed, while dihydropyridazines in the presence of Cu(II) salts yield pyridazines. Similarly, the oxidations of cyclohexane, adamantane and methylcatechol to benzoquinone, and amines to nitriles have been performed. The conversion of aldehydes to nitriles and benzyl radical cyclizations to butyrolactones have been achieved. Protection and deprotection, and various other Cu(II) halide-mediated reactions are also discussed.

ChemInform Abstract: Copper‐, Silver‐, and Gold‐Catalyzed Migratory Cycloisomerization Leading to Heterocyclic Five‐Membered Rings

“…93 The nature of the base required for the selective formation of the 3-acyloxy regioisomer supported possible involvement of allene intermediate 37, which is generated upon initial prototropic rearrangement of the substrate. Based on further mechanistic studies involving 17 O-labeled substrates, we proposed that this formal 1,2-acyloxy-group migration 94,95 likely occurs through the involvement of a dioxolenylium intermediate. 96 …”

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…302 Later, it was found that Cu(I)- or Cu(II)-salts were equally efficient in this transformation. 303 It was shown that di-, tri-, and tetrasubstituted pyrroles 3-29 with different substitution patterns could readily be synthesized using this method (Scheme 182). It should be noted that in the case of substrates 3-28 bearing terminal alkyne (R 4 = H), a spontaneous cycloisomerization was observed.…”

Two unusual mixed-valent trinuclear CuII2CuI complexes containing copper(i) tribromide dianion as bridging ligand: Identification of an unprecedented doubly hydrogen-bonded water dimer

“…The bromination of the ligands is not surprising as CuBr 2 is an effective reagent for the bromination of activated aromatics. 28,29 The aryl bromination reaction produces cuprous bromide and hydrogen bromide as side-products (according to: Ar-H + 2CuBr 2 ¼ Ar-Br + H-Br + 2CuBr). However, rather surprisingly bromination of the ligand (L 2 ) did not take place in the case of complex 2 indicating that substitution of the H-atom of the aldehyde by a methyl group prevents the ligand from bromination i.e.…”