Copper(II)‐Catalyzed Nitroaldol (Henry) Reactions: Recent Developments

Self‐assembled copper(II) complexes are described as effective catalysts for nitroaldol (Henry) reactions on water. The protocol involves a heterogeneous process and the catalysts can be recovered and recycled without loss of activity. Further, C2‐symmetric N,N′‐substituted chiral copper(II) salan complexes are found to be more effective catalysts than chiral copper(II) salen complexes for reactions in homogeneous catalysis, with high enantioselectivities. The reactions involve bifunctional catalysis, bearing the properties of a Brønsted base, as well as a Lewis acid, to effect the reaction in the absence of external additives.     

The Construction of Molecular Complexity from Functionalized Alkylidenecyclopropanes (FACPs)

As a special family of cyclopropanes, alkylidenecyclopropanes (ACPs), exhibit outstanding physical and chemical activities, which provide opportunities to participate in fascinating chemical transformations to access cyclopropane-containing units without ring-opening processes and other unavailable compounds through conventional routes with ring-opening processes owing to their strain-driven reactivity and synthetic accessibility. Nowadays, intramolecular reactions of methylenecyclopropanes (MCPs) or ACPs with adjacent functionalities have emerged as a powerful synthetic protocol for the construction of a variety of polycyclic and heterocyclic compounds with different sized skeletons through catalytic methods. Recently, we put forward the concept of functional alkylidenecyclopropanes (FACPs) and in this Minireview, we will summarize the reactions of FACPs after 2016 including several important early works from three aspects: 1) reactions with distal C−C bond cleavage, 2) reactions with proximal C−C bond cleavage (including ring-expansion reactions), and 3) reactions without C−C bond cleavage.     

Iron(iii) chloride-catalyzed mechanochemical cascade synthesis of highly-substituted pyrrolyl indoles

Iron(iii) chloride has been found to serve as an efficient catalyst for a mechanochemical (ball milling) one-pot four- component cascade reaction of phenyl glyoxal, anilines, indoles and activated alkyne affording highly-substituted 3-(1H-pyrrol-2-yl)-1H-indoles. The procedure is beneficial because of mild conditions, easily available starting materials, cheap catalyst and possibility for scaling.     

Direct synthesis of Cbz-protected (2-amino)-6-(2-aminoethyl)pyridines

A novel series of (2-amino)-6-(2-aminoethyl)pyridines were prepared by a convenient Suzuki-Miyaura coupling approach from 2-amino-6-bromopyridines. Benzyl vinylcarbamate was first treated with 9-BBN followed by aqueous NaOH and then the appropriate bromopyridine precursors were added into the mixture. The mixture was finally heated in presence of a palladium catalyst to provide the corresponding products in overall high yields. The procedure is extended to the preparation of related pyrazine and pyrimidine compounds as well as (2-amido)- and (2-alkoxy)-6-(2-aminoethyl)pyridines.     

Pd-catalyzed couplings of (α-fluoro)vinyl tris(trimethylsilyl)germanes

The (α-fluoro)vinyl tris(trimethylsilyl)germanes undergo Pd-catalyzed cross-couplings with aryl and alkenyl halides upon oxidative treatment with hydrogen peroxide under basic aqueous conditions to give access to fluoroalkenes and fluorodienes with retention of stereochemistry.     

Synthesis of ferrites: Thermal analysis of some transition metal tris(maleato)ferrates(III)

Thermal analysis of some transition metal ferrimaleate precursors, M₃[Fe(mal)₃]₂·xH₂O (M=Mn, Co, Ni, Cu) has been studied in static air atmosphere from ambient to 600°C. Various physico-chemical techniques, i.e. TG, DTG, DTA, XRD, IR, Mössbauer spectrometry, have been employed to characterize both the intermediates and final products. After dehydration the anhydrous precursors undergo decomposition to yield an iron(II) intermediate, M[Fe^II(mal)₂] (M=Mn, Co, Ni, Cu) in the temperature range 160-275°C. A subsequent oxidative decomposition of iron(II) species leads to the formation of -Fe₂O₃ and MO in the successive stages. Finally a solid-state reaction occurs between the oxides above 400°C resulting in the formation of transition metal ferrites, MFe₂O₄. The ferrites have been obtained at much lower temperature and in less time than in the conventional ceramic method.This revised version was published online in November 2005 with corrections to the Cover Date.     

p-(tricyanovinylidene)phenylhydrazones. Nucleophilic attack on carbon-carbon double bonds

The dispacement of a —CN group inp-(tricyanovinylidene)-phenylhydrazones, induced by amines, is investigated. The rate of the reaction is dependent on the polarity of the solvent and the observed second-order rate coefficientsk _obs ² for the —CN displacement increase with the amine concentration. A X-ray analysis of one of the substituted compounds is also reported.This work was supported by Ministero Pubblica Istruzione (Rome, 60%).     

Tris(polymethoxyphenyl)bismuth derivatives: Synthesis and reactivity

Tris-(polymethoxyphenyl)bismuth diacetate and dichloride derivatives react with C-nucleophiles in basic medium, as well as with N- and O-nucleophiles under copper catalysis to give good to high yields of the corresponding C-, N- and O-arylation products.     

Model studies on a diastereoselective synthesis of the C(33)-C(37) fragment of Amphotericin B

A new, short and highly diastereoselective synthetic route aiming at the C(33)-C(37) fragment of Amphotericin B has been developed. Studies with a model aldehyde (benzaldehyde) have given very promising results: the desired stereochemistry of all four stereocenters of the target molecule has been achieved with high diastereoselection. The stereochemistry of three key intermediates and the target segment has been confirmed by X-ray crystallography.     

SE(P): Electrophilic Substitution at Phosphorus

Reactions belonging to the formal category of electrophilic substitutions at phosphorus are classified according to mechanism and the coordination number of the phosphorus atom.     

Temperature-programmed surface reactions (TPSR) on heterogeneous surfaces

On the basis of calculations using a simple model of the energetic heterogeneity of a solid surface (assuming linear dependence of activation energy of desorption of the reactant on the degree of coverage), it is shown that both the degree of conversion and the course of desorption of the reactants are strongly influenced by the degree of heterogeneity assuming non-isothermal conditions. In contrast to a homogeneous solid surface, the degree of conversion for a heterogeneous surface depends strongly on the initial coverage of a catalyst by reactant. Possibilities for kinetic evaluation are indicated from the modelling calculations.     

Synthesis of bridged nicotinates having [n](2,5)pyridinophane skeletons (n=8-14)

Synthesis of various bridged nicotinates 6 having [n](2,5)pyridinophane skeletons (n=8-14) was accomplished by the unique pyridine-formation reaction of methyl propiolate with a series of formyl-substituted (vinylimino)phosphoranes 5, which were prepared from the corresponding cycloalkanones 1 via Vilsmeier-Haack formylation giving chloro-substituted cycloalkenals 2, their thermal and photochemical transformation to formyl azirines 4, and the following ring-opening reactions with triphenylphosphine. The HPLC analysis of [11](2,5)pyridinophane derivatives, (S_p,S)-14 and (R_p,S)-14, showed that these diastereomers rapidly epimerize themselves at room temperature and that their planar-chirality was thermodynamically less stable as compared to the corresponding [11](2,5)cyclophane systems.     

Reactive E=C(p‐p)π‐Systems. 56 [1] Attempted Preparation of PhE=C(CF3)2 by Reactions of Hexafluoroacetone with PhE(SiMe3)2 (E = As,P)

The chance to prepare sterically and inductively stabilized arsa‐ and phosphaalkenes of the type PhE=C(CF₃)₂ (E = As, P) by reacting phenyl‐bis(trimethylsilyl)‐arsane ( 1 ) and ‐phosphane ( 5 ), respectively, with hexafluoroacetone (HFA) was investigated. The insertion of the carbonyl function in one of the Si–E bonds was found to occur at temperatures between ?78 and 20 °C. The elimination of hexamethyldisiloxane, which in case of acylamides and ketones spontaneously follows the insertion and in case of RE(SiMe₃)–CR′₂(OSiMe₃) at least can be initiated by solid sodium hydroxide as catalyst, turned out to be impossible for the primary products PhE(SiMe₃)–C(CF₃)₂‐OSiMe₃ [E = As ( 2 ), P ( 6 )]. 2 and 6 were characterized by analytical (C, H) and spectroscopic methods (IR, NMR, MS).     

Reactions of silylated Schiff bases with organotitanium(IV) and organotin(IV) chlorides

The interactions of silylated dibasic quadridentate Schiff bases derived fromo-hydroxyacetophenone and ethylenediamine and orthophenylenediamine with (π-C₅H₅)TiCl₃, (π-C₅H₅)(MeO)TiCl₂, (MeO)₂TiCl₂, Me₂SnCl₂ and MeSnCl₃ yield a new series of organotitanium(IV) and tin(IV) compounds. The reactivity of (π- C₅H₅)Ti(L₁)Cl and MeSn(L₁)Cl, towards MeSH, Me₂NSiMe₃, SiMe₃N₃ and Me₃SiC = CPh are also described. The structures for the compounds isolated are proposed on the basis of elemental analyses, molecular weights, IR and¹H nmr spectroscopic studies.