Anodic coupling reactions: exploring the generality of Curtin-Hammett controlled reactions

Intramolecular anodic olefin coupling reactions can be compatible with the presence of dithioketal protecting groups even though the dithioketal oxidizes at a lower potential than either of the groups participating in the cyclization. In such cases, product formation is controlled by the Curtin-Hammett Principle. In this study, the generality of such reactions is examined along with the use of alternative reaction conditions to suppress unwanted side reactions.     

Anodic cyclization reactions: probing the chemistry of N,O-ketene acetal derived radical cations

The chemical reactivity of radical cations derived from N,O-ketene acetals has been examined and compared with the reactivity of radical cations derived from both ketene dithioacetals and enol ethers. Synthetically, the N,O-ketene acetal radical cations lead to more efficient cyclization reactions than either the ketene dithioacetal or enol ether derived radical cations. Cyclic voltammetry experiments using allylsilane trapping groups show that the efficiency of these cyclizations is not due to the N,O-ketene acetal radical cations being more reactive but rather more stable to decomposition. Finally, cyclizations using chiral oxizolidinones were examined.     

Anodic coupling reactions: a sequential cyclization route to the arteannuin ring skeleton

A pair of intramolecular anodic olefin coupling reactions has been used to construct the arteannuin ring skeleton. Both coupling reactions took advantage of a furan ring as one of the coupling partners. In the first, it was found that an enol ether derived from an aldehyde was not an effective initiating group for the reaction. Instead, the cyclization benefited strongly from the use of a N,O-ketene acetal initiating group. In the second cyclization, an endocyclic enol ether was coupled to the furan ring. This second electrolysis reaction generated the key tetrasubstituted carbon at the center of the arteannuin ring skeleton.     

Tetraorganoindates as nucleophilic coupling partners in Pd-catalyzed cross-coupling reactions

In situ-generated tetraorganoindate complexes from the reaction of 1 equiv of indium trichloride with 4 equiv of appropriate organometallics are efficient nucleophiles in Pd-catalyzed cross-coupling reactions. In this novel reaction tetraorganoindates containing methyl, 1 degree- and 2 degree-alkyl, vinyl, alkynyl, and aryl groups transfer the four organic groups to a variety of electrophiles with high atom efficiency. [reaction: see text]     

Anodic coupling reactions: probing the stereochemistry of tetrahydrofuran formation. A short, convenient synthesis of linalool oxide

[reaction: see text]. Intramolecular coupling reactions between enol ether radical cations and oxygen nucleophiles are primarily governed by stereoelectronics. By taking advantage of this observation, a tetrahydrofuran building block for use in constructing (+)-linalool oxide and rotundisine has been synthesized in four steps from a commercially available starting material. The synthesis of (+)-linalool oxide has been completed.     

N,Se-Acetals: Preparation and use in diastereoselective radical reactions

A new facile synthesis of N,S- and N,Se-acetals starting from aldehydes and primary amines is presented (Schemes 3–5). These acetals are used as precursors for stereoselective radical deuteration and allylation reactions (Schemes 6 and 7, Tables 1 and 2). The stereochemical outcome of the reactions depends on the radical trap and the substituents at the N-atom. Deuterations give always anti products with moderate to high selectivities. The allylation reactions give either syn or anti products with low to moderate selectivities. The observed stereoselectivities can be explained with a model based on minimization of A^1,3 strain and are controlled by steric and stereoelectronic effects.     

Intramolecular anodic olefin coupling reactions: the use of a nitrogen trapping group

Anodic olefin coupling reactions using a tosylamine trapping group have been studied. The cyclizations are favored by the use of a less-polar radical cation and more basic reaction conditions. The most significant factor for obtaining good yields of cyclic product is the use of the more basic reaction conditions. The cyclizations allow for the rapid synthesis of substituted proline derivatives.     

Simple palladium(II) precatalyst for Suzuki-Miyaura couplings: efficient reactions of benzylic, aryl, heteroaryl, and vinyl coupling partners

trans-PdBr(N-Succ)(PPh3)2 (1) is a universally effective precatalyst for Suzuki-Miyaura cross-couplings of benzylic halides with aryl- or heteroarylboronic acids. Substituted aryl halides and halogenated cyclic enones can be cross-coupled with aryl- or vinylboronic acids in excellent yields. Catalyst recycling is also demonstrated.     

Asymmetric synthesis via acetal templates. 12. Highly diastereoselective coupling reactions with a ketene acetal. An efficient,asymmetric synthesis of R-(+)-α-lipoic acid

TiCl₄ catalyzes the essentially quantitative coupling of chiral acetals $\text{1}$ with 1-$\text{t}$-butoxy-1-$\text{t}$-butyldimethylsilyloxyethene $\text{2}$ to generate β-alkoxycarboxylates in which the new asymmetric center is formed with excellent diastereoselection. β-hydroxycarboxylic acids of high ee result from removal of the chiral auxiliary. The procedure has been applied to the synthesis of R-(+)-α-lipoic acid $\text{10.}$     

Anodic cyclization reactions: the total synthesis of alliacol a

An anodic cyclization-Friedel Crafts alkylation strategy has been used to rapidly assemble the core ring system of alliacol A and to complete a formal total synthesis of the natural product. The anodic cyclization reaction was used to effect the coupling of a nucleophilic furan ring to the normally nucleophilic carbon of a silyl enol ether. The substrate for this initial cyclization reaction contained all of the carbons needed for completing the total synthesis. The electrolysis proceeded in high yield and could be accomplished with the use of a 6 V lantern battery.     

Luminescent atropisomeric N,N-chelating ligands from copper-catalyzed one-pot C-N and C-C coupling reactions

New atropisomeric N,N-chelating ligands with a 3,3'-bis[2-(2'-py)-indolyl] unit have been achieved via one-pot reactions that involve the formation of multiple C-N bonds between an indolyl and a brominated benzene and the indolyl 3,3'-C-C coupling. The new ligands display distinct blue intramolecular excimer emission (lambda(max) = 445 nm). Cu(I) ions bind to the new N,N-chelate ligands with a homochiral selectivity. The complex [Cu(bpib)2][BF(4)] (bpib = bis{3,3'-[N-phenyl-2-(2'-py)-indolyl]}) crystallizes as chiral crystals, thus allowing enantiomeric separation.     

Anodic cyclization reactions: reversing the polarity of ketene dithioacetal groups

Intramolecular coupling reactions of ketene dithioacetal groups with enol ether and alcohol nucleophiles have been studied. The reactions were initiated by an anodic oxidation of the ketene dithioacetal and proved to be compatible with the formation of five- or six-member rings, as well as the stereoselective generation of quaternary carbons.     

Response reactions: equilibrium coupling

It is pointed out and illustrated in the present paper that if a homogeneous multiple equilibrium system containing k components and q species is composed of the reactants actually taken and their reactions contain only k + 1 species, then we have a unique representation with (q - k) stoichiometrically independent reactions (SIRs). We define these as coupling reactions. All the other possible combinations with k + 1 species are the coupled reactions that are in equilibrium when the (q - k) SIRs are in equilibrium. The response of the equilibrium state for perturbation is determined by the coupling and coupled equilibria. Depending on the circumstances and the actual thermodynamic data, the effect of coupled equilibria may overtake the effect of the coupling ones, leading to phenomena that are in apparent contradiction with Le Chatelier's principle.     

N-vinylpyridinium and -ammonium tetrafluoroborate salts: new electrophilic coupling partners for Pd(0)-catalyzed Suzuki cross-coupling reactions

N-Vinylpyridinium and -trialkylammonium tetrafluoroborate salts represent a new class of electrophilic coupling partner for Pd(0)-catalyzed Suzuki cross-coupling reactions and give very good to excellent yields of products with a wide range of boronic acids. The salts are easily prepared from activated acetylenes and pyridinium or trialkylammonium tetrafluoroborates to form crystalline, air-stable, and nonhygroscopic crystals. [reaction: see text].     

Alkene-directed, nickel-catalyzed alkyne coupling reactions

In alkene-directed, nickel-catalyzed coupling reactions of 1,3-enynes with aldehydes and epoxides, the conjugated alkene dramatically enhances reactivity and uniformly directs regioselectivity, independent of the nature of the other alkyne substituent (aryl, alkyl (1 degrees , 2 degrees , 3 degrees )) or the degree of alkene substitution (mono-, di-, tri-, and tetrasubstituted). These observations are best explained by a temporary interaction between the alkene and the transition metal center during the regioselectivity-determining step. The highly substituted 1,3-diene products are useful in organic synthesis and, in conjunction with a Rh-catalyzed, site-selective hydrogenation, afford allylic and homoallylic alcohols that previously could not be prepared in high regioselectivity (or at all) with related Ni-catalyzed alkyne coupling reactions.     

Anodic reactions of sulphate in molten salts

Electrochemical behaviour of sulphate under anodic polarization in molten sodium chloride, cryolite and sodium fluoride was investigated by cyclic voltammetry and chronopotentiometry at the temperatures of 820°C, 1010°C, and 1000°C, respectively. Using a platinum working electrode, two waves were observed on the chronopotentiograms in the systems: NaCl-Na₂SO₄ and Na₃AlF₆-Na₂SO₄. The first wave was attributed to the formation of oxygen. The second wave probably originated from the reaction of oxygen with platinum, or from oxidation of SO₃ decomposition products. Three waves were observed for the anodic process of sulphate ions dissolved in molten sodium fluoride. The first wave was attributed to the formation of oxygen. The second and the third wave were attributed to the formation of PtO and PtO₂. This conclusion was supported by cyclic voltammetry experiments of the in-situ formed sulphide in molten NaCl at 820°C and by chronopotentiometry on a gold working electrode in the system NaCl-Na₂SO₄, where no anodic wave was observed.     

Alkenyl bromides: useful coupling partners for the palladium-catalysed coupling with heteroaromatics via a C-H bond activation

Alkenyl bromides were found to be useful reactants for the palladium-catalysed direct C-H activation/functionalisation reaction of heteroaromatics such as benzoxazole or benzothiazole. Moderate to good yields of coupling products were obtained using both α- and β-substituted alkenyl bromides or even the trisubstituted alkenyl bromide 2-bromo-3-methylbut-2-ene. This reaction is environmentally attractive as it provides only HX associated to the base as a by-product.     

Chemical polarisation of 15N and 13C nuclei in diazo coupling reactions

Chemical polarisation of nitrogen and carbon nuclei in the decomposition and diazo coupling reactions of benzenediazonium fluoborate has been investigated. If homo- and heterolytic processes run in parallel in a multistage reaction sequence, then the nuclear polarisation created in a free-radical reaction can be nearly quantitatively carried over to products of rapid ionic reactions such as azo dyes.