Synthetic utility of gem-dibromomethylarenes in organic synthesis

Gem-dibromomethylarenes are considered as one of the valuable building blocks in the synthetic field because of their broad range of synthetic applications. These synthons serve as useful intermediates in accessing a varied range of (hetero) aromatic frameworks that can act as vital scaffolds in agrochemicals, medicinal chemistry, material sciences, etc. The additional organic transformations that can be performed using these vital reagents highlights its significance in the area of organic synthesis. This review aims at displaying some discoveries and subsequent improvements of this vital intermediate as an important building block in organic transformations.     

Copper(II) in organic synthesis. IV Reaction of the copper(II) acetate complex of isatin-3-arylhydrazones with dimethyl acety-lenedicarboxylate.

The copper(II) acetate complex of isatin-3-phenylhy-drazone (2a) reacted with dimethyl acetylenedicarboxylate (DMAD) by two competitive pathways: a Cu⁺⁺ oxidation of the ligand and a [2+2] cycloaddition. The former reaction gave 3-car- benindolin-2-one (13) which reacted with DMAD in a l,3-dipolar cycloaddition, to give 3a. This was synthesized by an independent route. The phenyl radical, generated in the same process, was trapped by three DMAD and gave $\text{4a}$. The [2+2] cycloaddition gave a spiro adduct 10 which, by electrocyclic ring opening and intramolecular cyclization, allowed isolation of a pyridazino [3,4-b] indole (|5a). The reaction was performed on $\text{p}$-chlorophe-nylhydrazone 1b and the structure of 5b was demonstrated by X-ray analysis. A rationalization of the reactivity was attempted in terms of MO interactions of the reactants.     

Synthetic utility and mechanistic implications of the Fries rearrangement of hydroquinone diesters in boron trifluoride complexes

Reactions of boron trifluoride methyl and ethyl etherate complexes with hydroquinone diesters yield monomethyl and monoethyl derivatives of acetylhydroquinones. The use of sterically hindered boron trifluoride etherate complexes results in acetylhydroquinone derivatives. This procedure represents a one-step synthesis of acetylhydroquinone derivatives, important building blocks for a variety of synthetic applications.     

Stanna-Brook rearrangement of carboxylic acid derivatives. Synthetic utility and mechanistic studies

[reaction: see text] The reaction of R(3)SnLi with carboxylic acid derivatives proceeds through a novel, very fast stanna-Brook rearrangement that generates alpha-alkoxyorganolithium compounds as intermediates. The outcome of these reactions depends on the nature of the carboxyl derivatives. Reaction of R(3)SnLi with ester derivatives gives rise to coupled products through a novel C-C bond formation reaction. Experimental evidence of the detailed reaction mechanism is provided.     

Solid state reactions of organopentafluorosilicates with copper(I) and copper(II) salts

Two types of solid state reaction of K₂[RSiF₅] have been developed: (1) CuCl promoted homo coupling of alkenyl- and phenyl-silicates, and (2) formation of RH fraom alkyl- and alkenyl-silicates by heating with CuF₂·2H₂O.     

Copper(II)-mediated oxidation of 1,2-dioxime to furoxan

1,2-Dioximes undergo oxidative transformation mediated by copper(II) ions in acetonitrile to form the corresponding furoxans in high yields. A series of 1,2-dioximes including aliphatic, aromatic, and heterocyclic dioximes were oxidized using these mild conditions.     

Structural and mechanistic investigations of the oxidation of dimethylplatinum(II) complexes by dioxygen

The oxidation of (tmeda)Pt(II)(CH(3))(2) (1, tmeda = N,N,N',N'-tetramethylethylenediamine) to (tmeda)Pt(IV)(OH)(OCH(3))(CH(3))(2) (3) by dioxygen in methanol proceeds via a two-step mechanism. The initial reaction between (tmeda)Pt(CH(3))(2) and dioxygen yields a hydroperoxoplatinum(IV) intermediate, (tmeda)Pt(OOH)(OCH(3))(CH(3))(2) (2), which reacts with a second equivalent of (tmeda)Pt(CH(3))(2) to afford the final product 3. Both 2 and 3 have been fully characterized, including X-ray crystallographic structure determinations. The effect of ligand variation on the oxidation of several dimethylplatinum(II) complexes by 2 as well as by dioxygen has been examined.     

Extensively Conjugated Dianionic Tetrathiooxalate-Bridged Copper(II) Complexes for Synthetic Metals

Using a unique three-solvent biphasic method, we have prepared and characterized three new fully conjugated, chalcogen-rich, bridged copper(II) complexes for the preparation of molecular conductors and magnetic materials, having the general formula (Bu(4)N)(2){tto[Cu(L)](2)} (tto = C(2)S(4)(2)(-) = tetrathiooxalato; L = mnt = C(4)N(2)S(2)(2)(-) = 1,2-dicyanoethene-1,2-dithiolato for complex 2, dsit = C(3)Se(2)S(3)(2)(-) = 2-thioxo-1,3-dithiole-4,5-diselenolato for complex 3, dmid = C(3)OS(4)(2)(-) = 2-oxo-1,3-dithiole-4,5-dithiolato for complex 4a). The single-crystal X-ray structures of 2 and 3 have been determined: 2, (Bu(4)N)(2){tto[Cu(mnt)](2)}, monoclinic, space group C2/m, a = 19.549(4) ?, b = 13.519(3) ?, c = 10.162(2) ?, beta = 90.33(1) degrees, Z = 2; 3, (Bu(4)N)(2){tto[Cu(dsit)](2)}, monoclinic, space group P2(1)/c, a = 9.903(1) ?, b = 15.589(1) ?, c = 18.218(1) ?, beta = 90.40(1) degrees, Z = 2. Complex 2 displays perfect planarity, while 3 shows a slight tetrahedral distortion at the metal centers, resulting in a dihedral angle of 24.86(3) degrees. Cyclic voltammetry of (Bu(4)N)(2){tto[Cu(mnt)](2)} (2), (Bu(4)N)(2){tto[Cu(dsit)](2)} (3), and (Bu(4)N)(2){tto[Cu(dmid)](2)} (4a) shows each complex to exhibit two reversible redox processes which can be attributed to {tto[Cu(L)](2)}(2)(-) right arrow over left arrow tto[Cu(L)](2)}(-) and {tto[Cu(L)](2)}(1)(-) right arrow over left arrow {tto[Cu(L)](2)}(0) couples. The structural and electronic properties of 2, 3, and 4a will be compared to those of the recently communicated analogous complex (Bu(4)N)(2){tto[Cu(dmit)](2)} (1).     

Copper(II) catalyzed aromatization of tetrahydrocarbazole: An unprecedented protocol and its utility towards the synthesis of carbazole alkaloids

An efficient protocol for the aromatization of tetrahydrocarbazole is described by using catalytic copper(II) chloride dihydrate in DMSO. This newly established methodology has utilized towards the synthesis of naturally occurring carbazole alkaloids, namely 3-methylcarbazole, 3-formyl carbazole, glycozoline, glycozolicine and clauszoline-K. In addition, the protocol is generalized for the aromatization of N-substituted tetrahydrocarbazole, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline and 1,2,3,4-tetrahydro β-carboline to give the corresponding heteroaromatic compounds from very good to excellent yield. Moreover, this method has been proven to be tolerant to a broad range of functional groups with excellent yields.     

Copper(II)-catalyzed oxidation of d-alpha-tocopherol by oxygen in aqueous solution

alpha-Tocopherol (alpha-Toc) was solubilized in aqueous solutions using 13 solubilizing agents and the products of oxidation by oxygen in the presence and the absence of Cu(II) were analyzed by HPLC. In the presence of Cu(II), the oxidation was accelerated and 5-formyl-7,8-dimethyltocol and alpha-tocoquinone were the major oxidation products. Their yields greatly increased in the presence of Cu(II). The yields and the rates of formation of the products were dependent on the properties of solubilizing agents and other conditions as well as the presence of Cu(II) or other metal ions. It is suggested that slight changes in the structure of the solubilizing agents affect the course of the reaction.     

Synthetic and mechanistic studies on asymmetric cyanohydrin synthesis using a titanium(salen) bimetallic catalyst

A bimetallic titanium(salen) complex 1 was found to catalyse the asymmetric addition of ethyl cyanoformate to aldehydes. Best results were obtained using 5 mol% of the catalyst at −40 °C and under these conditions, both aromatic and aliphatic aldehydes were converted into cyanohydrin carbonates with up to 99% enantiomeric excess. The same catalyst could also be used to catalyse the asymmetric addition of potassium cyanide to aldehydes in the presence of propionic anhydride, leading to cyanohydrin esters. Mechanistic studies showed that the enantiomeric excess of the product increased during the early stages of this reaction. However, by adding a ‘sacrificial aldehyde’ this effect could be eliminated. The structure of the catalyst in solution was investigated using variable concentration, variable temperature and variable solvent NMR studies. These experiments showed that the catalyst exists as a mixture of monometallic 4 and bimetallic 1 species, a result which is consistent with previous mechanistic studies on the asymmetric addition of trimethylsilyl cyanide to aldehydes and ketones catalysed by the same catalyst. A mechanistic rationale for all of these observations is reported.     

Copper(II) and nickel(II) complexes of mono-oxocyclam(5-oxo-1,4,8,11-tetraazacyclotetradecane). Synthetic and potentiometric studies

Summary The macrocyclic mono-oxotetraamine, 5-oxo-1,4,8,11-tetraazacyclotetradecane (mono-oxocyclam=LH) has been prepared by reaction of methyl acrylate with 2,3,2-tetra(1,9-diamino-3,7-diazanonane). The protonation constants of the ligand are log K₁=9.40, log K₂=6.65 and log K₃=2.87 at 25 °C (I=0.1 mol dm^–3 NaClO₄). Detailed potentiometric studies of the interaction of the base with copper(II) and nickel(II) have been carried out. In the pH range 2.5–7.0 two complexes, [CuLH]²⁺ and [CuL]⁺, form; the deprotonated complex being 100% abundant at pH 7. For nickel(II), only [NiL]⁺ forms (log _11–1 = 3.90), the yellow low spin nickel complex reaching its maximum concentration above pH 6. The [CuL][ClO₄] · H₂O and [NiL][ClO₄] 0.5 H₂O complexes have been characterised in the solid state. The nickel(II) complex is square planar with a d-d band at 22625 cm^–1.     

Double Hydrated Cobalt(II) Copper(II) and Nickel(II) Copper(II) Ammine Diphosphates

Synthesis of amorphous and crystalline double hydrated cobalt copper and nickel copper ammine diphosphates with a coordination structure is described.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 369–372.Original Russian Text Copyright © 2005 by Voitenko, Zhilyak, Kopilevich.     

Copper(II)-catalysed aerobic oxidation of primary alcohols to aldehydes

[CuBr2(2,2'-bipyridine)] catalyses the selective and very mild aerobic oxidation of primary alcohols to aldehydes in acetonitrile:water (2:1) in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) and a base as cocatalysts.     

Silafunctional compounds in organic synthesis. 21. Hydrogen peroxide oxidation of alkenyl(alkoxy)silanes

The carbon-silicon bond in alkenyl(alkoxy)silanes is readily cleaved by hydrogen peroxide to form the corresponding aldehydes, carboxylic acids or ketones, depending upon the nature of the alkenyl group and the reaction conditions.     

Copper(II) mediated facile and ultra fast peptide synthesis in methanol

A novel, ultrafast, mild and scalable amide bond formation strategy in methanol using simple thioacids and amines is described. The mechanism suggests that the coupling reactions are initially mediated by CuSO(4)·5H(2)O and subsequently catalyzed by in situ generated copper sulfide. The pure peptides were isolated in satisfactory yields in less than 5 minutes.     

Electrophilic Copper(II) → Metal(II) Substitution in Gelatin-Immobilized Copper(II) Hexacyanoferrate(II) Matrix Implants

Contact of thin layers of gelatin-immobilized copper(II) hexacyanoferrate(II) matrices with aqueous solutions of Co(II), Ni(II), Zn(II), and Cd(II) chlorides results in partial substitution of these ions for Cu(II) to give (dd)-heterobinuclear hexacyanoferrates(II) of copper(II) and the corresponding double-charged ion.     

Synthetic 3-O-methylmannose-containing polysaccharides (sMMPs): design and synthesis

With the hope of mimicking the chemical and biological properties of natural 3-O-methylmannose-containing polysaccharides (MMPs), synthetic 3-O-methylmannose-containing polysaccharides (sMMPs) were designed and synthesized in a convergent manner. With little modification of the Mukaiyama glycosidation, high alpha-selectivity (>50:1 approximately >20:1) and yields (79 approximately 74%) were achieved for the key glycosidation steps. The exceptionally high alpha-selectivity observed was shown to be consequent to the selective anomerization of beta- to alpha-anomer under the glycosidation conditions. This glycosidation is well suited for a highly convergent oligosaccharide synthesis, particularly because of excellent chemical yields even when using approximately equal-sized donors and acceptors in an approximately 1:1 molar ratio. An iterative reaction sequence allowed the growing oligosaccharide to double in size after each cycle and led to an efficient synthesis of sMMP 8-, 12-, and 16-mers 18-20.