Brønsted acid-promoted cyclizations of siloxyalkynes with arenes and alkenes

We have described the first Br?nsted acid-mediated cyclizations of siloxyalkynes with simple arenes and alkenes to afford substituted tetralone and cyclohexenone derivatives. The most notable aspect of the carbocyclizations involving siloxyalkynes is the ability to employ a range of substrates that are not restricted to those containing electron-rich arenes and alkenes. The key mechanistic feature of the reaction is the generation of a highly reactive ketenium ion upon protonation of siloxyalkyne. We believe that the low nucleophilicty of the counteranion is crucial for enabling the formation and effective interception of this highly reactive intermediate.     

Lewis acid-promoted reactions of ethenetricarboxylates with γ-CF3-substituted propargyl alcohols

The Lewis acid-promoted reaction of an ethenetricarboxylate derivative (1) with CF₃-substituted propargyl alcohols has been examined. Reaction of γ-CF₃ propargyl alcohols in the presence of zinc bromide gave five-membered CF₃-containing tetrahydrofurans in 66-85% yield. The CF₃ group activates alkyne as an electron-withdrawing group. On the other hand, reaction of γ-trifluoromethyl-α-aryl propargyl alcohols 2 with 1 in the presence of 1 equiv of SnCl₄ gave cyclobutane derivatives 6 in 29-49% yield. Formation of cyclobutane 6a arises from the [2+2] cycloaddition between ethenetricarboxylate 1 and chloroallene 8, which is produced by the reaction of propargyl alcohol 2a and SnCl₄.     

Copper(I) promoted CC bond forming reactions: direct activation of allyl alcohols

Allylic alcohols, acetates, carbonates and chlorides can be activated by copper(I) salts towards nucleophilic substitution by carbon nucleophiles under relatively mild conditions.     

Amberlyst-15: an efficient and reusable catalyst for the Friedel-Crafts reactions of activated arenes and heteroarenes with α-amido sulfones

The heterogeneous Amberlyst-15 catalyst displays efficient catalytic properties for the Friedel-Crafts reactions between an activated arenes or heteroarenes and α-amido sulfones. Various α-amido sulfones on treatment with 1,2,4-trimethoxy benzene give the Friedel-Crafts reaction products in very good yield. The reactions with heteroarenes show moderate yield of the product. The catalyst can be easily recycled without significant loss of activity.     

Gallium trichloride-mediated reactions of ‘double’ donor–acceptor cyclopropanes with alkenes and dienes

The reactions of ‘double’ donor–acceptor cyclopropanes containing a p- or m-phenylene moiety with alkenes or dienes in the presence of GaCl₃ comprise formation of gallium 1,2-zwitterionic intermediates, the structure of final products being substrate dependent. In contrast to the para-or meta-isomers, reaction of 2,2'-(1,2-phenylene)bis(cyclopropane-1,1-dicarboxylate) does not involve alkene and affords isomeric tricyclo[6.2.2.0^2,7]dodeca-2,4,6-triene-9,9,11,11-tetra-carboxylate, a product of intramolecular rearrangement.     

Intramolecular coupling of allyl carboxylates with allyl stannanes and allyl silanes: a new type of reductive elimination reaction?

The palladium-catalyzed intramolecular coupling of allyl stannanes with allyl carboxylates provides a general synthesis of five- and six-membered-ring carbocycles. The intramolecular coupling leads selectively to trans five-membered carbocycles and cis six-membered carbocycles, regardless of the cis or trans configuration of the allylic functions in the starting material. For example, the stereoselective synthesis of 10-epi-elemol demonstrated the cis configuration of the six-membered carbocycles. The related Oppolzer cyclization leads to lower yields, or fails completely, with substrates substituted at C-3 of the allyl and/or alkene terminus. The palladium-catalyzed intramolecular coupling of allyl silanes with allyl trifluoroacetates allows the synthesis of trans five-membered-ring carbocycles and requires the use of a bicyclic phosphite as the ligand. DFT calculations suggest that the preferred pathway for the intramolecular allyl/allyl coupling is by formation of the Cbond;C bond between the C-3 termini of the allyl ligands of bis(eta(3)-allyl)palladium complexes.     

Alkyl 3-nitroacrylates: Synthesis and reactions with cyclohexane-1,3-diones and Meldrum’s acid

A modified procedure was proposed for the synthesis of alkyl 3-nitroacrylates by nitroiodination of alkyl acrylates and subsequent dehydroiodination of iodonitropropanoates with triethylamine. Alkyl 3-nitroacrylates reacted with cyclohexane-1,3-dione, dimedone, and Meldrum’s acid in the presence of N,N,N-tri-methylanilinium hydroxide (Rodionov’s catalyst) in anhydrous methanol to give the corresponding Michael adducts.     

Copper(?) hexafluorophosphate: a dual functional catalyst for three-component reactions of methyl phenyldiazoacetate with alcohols and aldehydes or α-ketoesters

Oxonium ylides in situ generated from methyl phenyldiazoacetate and alcohols in the presence of CuPF₆(CH₃CN)₄ underwent an aldol-type reaction with aldehydes or α-ketoesters in a convergent, three-component fashion to give α-alkoxyl-β-hydroxyl acid derivatives in good yields.     

‘Bad’ distributions of good data: unusual statistics of structural databases

Structural Chemistry - Distributions of data taken from crystal structure databases, display unusual statistical properties like non-Gaussian shape, polymodality, and heavy tails. These features,...     

Cooperative catalysis with chiral Brønsted acid-Rh2(OAc)4: highly enantioselective three-component reactions of diazo compounds with alcohols and imines

An asymmetric three-component reaction of diazo compounds and alcohols with imines catalyzed cooperatively by a rhodium complex and a chiral Br?nsted acid provides a general and efficient entry to beta-amino-alpha-hydroxyl acid derivatives in high yields with excellent stereoselectivities.     

Substrate- and temperature-controlled divergence in reactions of alcohols with TosMIC catalyzed by BF3 · Et2O: Facile access to sulfinates and sulfones

An efficient BF₃?·?Et₂O-catalyzed divergent synthesis of sulfinate esters and sulfones through C–O and C–S bond formation has been achieved from alcohols and p-toluenesulfonylmethyl isocyanide (TosMIC). Various alcohols reacted smoothly with TosMIC under the present conditions at room temperature providing sulfinate esters exclusively. By tuning the reaction temperature, the alcohols that provide highly stabilized carbocation in the reaction medium afforded sulfones as sole products. This study was aimed at understanding the regioselectivity of ambidentate sulfinate ion and to elucidate the interpretation of sulfinate/sulfone scaffolds.     

‘Apples’ and ‘oranges’: comparing the structural aspects of biomineral- and ice-interaction proteins

The title of this review describes structural comparisons of protein classes whose task is to identify and interact with biological solids (minerals and ice). To date, the following trends have been noted: (1) biomineral-interaction proteins typically adopt unfolded, open conformations, and, where mineral binding motifs have been identified, these sequences exhibit structural trends towards extended, random coil, or other unstable secondary structures; (2) ice-interaction proteins typically adopt folded structures, featuring stable secondary structure preferences (α-helix, β-sheet, β-helix, etc.) and stable, planar ice binding motifs that exploit hydrophobicity and van der Waals’ interactions for ice binding.     

‘A rendezvous with an old flame’: revisiting olefin hydrogenation with new rhodium and iridium catalysts

A novel tridentate hemilabile ligand 2 containing phosphine, imine and pyridyl donor groups has been prepared in analogy with the synthesis of the known related ligand 1. The reaction of 1 or 2 with 〚Rh(COE)₂Cl〛₂ resulted in the formation of the neutral complexes 〚Rh(L)Cl〛. By a method using 〚M(diene)Cl〛₂ as starting material, cationic complexes of the type 〚M(diene)(L)〛X were also obtained (M = Rh, diene = NBD, L = 1, 2; M = Ir, diene = COD, L = 1; X = BF₄, OTf). A comparative study of the catalytic activity of the new complexes towards the hydrogenation of various olefins has been reported. In particular, the catalysts of the type 〚Rh(L)Cl〛 are remarkably active when prepared in situ, especially for the reduction of hindered olefins.     

‘Soft’ electroactive particles and their interaction with lipid membranes

Solid lipid nanoparticles (SLN) are widely used in pharmaceutical and cosmetic applications. SLN, incorporating approximately 10⁵ ferrocene units, as core-enriched redox active nanoparticles, were used as a model for probing interactions with solid-supported lipid membranes. Resonance Enhanced Surface Impedance Spectroscopy (RESI) is shown as a sensitive technique for monitoring real time interactions of the soft redox nanoparticles. Cyclic voltammetry is compared as an end of experiment technique.     

An unusual regiochemistry of reactions of a cyclohexenylphosphonate bearing a β-ethoxycarbonyl group with aldehydes

Reactions of lithiated ethyl 6-(dimethoxyphosphoryl)cyclohex-1-enecarboxylate with aliphatic, aromatic, and unsaturated aldehydes were studied and determined to proceed with α or δ regioselectivity. Such an unusual regioselectivity results from the contribution of two allylic carbanions: one, stabilized by the phosphonate moiety and the other stabilized by the carboethoxy group. The course of the reaction depends mainly on the structure of the aldehyde and the reaction conditions. The products of Horner-Wadsworth-Emmons reaction, including an analogue of some retinol metabolites, were formed under kinetic conditions whereas the δ-adducts were obtained as thermodynamic products.     

Enyne Meldrum´s acid derivatives: synthesis and Michael reactions with amines and thiols

Russian Chemical Bulletin - The Knoevenagel condensation of arylpropynals with Meldrum´s acid in the presence of Et3N affords 5-(3-arylprop-2-yn-1-ylidene)-2,2-dimethyl-1,3-dioxane-4,6-diones...     

СН functionalization of (hetero)arenes with ethyne and ethene moieties

Chemistry of Heterocyclic Compounds - This article provides an overview of the available literature data on direct CH functionalization reactions used for introducing alkenyl and alkynyl groups...     

Nucleophilic substitution reactions of alcohols with use of montmorillonite catalysts as solid Brønsted acids

We have developed an environmentally benign synthetic approach to nucleophilic substitution reactions of alcohols that minimizes or eliminates the formation of byproducts, resulting in a highly atom-efficient chemical process. Proton- and metal-exchanged montmorillonites (H- and Mn+-mont) were prepared easily by treating Na+-mont with an aqueous solution of hydrogen chloride or metal salt, respectively. The H-mont possessed outstanding catalytic activity for nucleophilic substitution reactions of a variety of alcohols with anilines, because the unique acidity of the H-mont catalyst effectively prevents the neutralization by the basic anilines. In addition, amides, indoles, 1,3-dicarbonyl compounds, and allylsilane act as nucleophiles for the H-mont-catalyzed substitutions of alcohols, which allowed efficient formation of various C-N and C-C bonds. The solid H-mont was reusable without any appreciable loss in its catalytic activity and selectivity. Especially, an Al3+-mont showed high catalytic activity for the alpha-benzylation of 1,3-dicarbonyl compounds with primary alcohols due to cooperative catalysis between a protonic acid site and a Lewis acidic Al3+ species in its interlayer spaces.