Nitrogen-containing Lewis Bases Research Articles

Organoboronic Acids: A Chance for Improving Photochemistry

Abstract: Photoredox catalysis as a powerful strategy for the activation of small molecules requires the use of reactants which are suitable to undergo single-electron transfer with the formation of radicals. In this perspective, we highlight the unique ability of organoboronic acid derivatives to form radicals under photoredox catalysis conditions with particular emphasis placed on the methods of activation of B-C bonds. Key to facilitate the activation relies on use of easily oxidizable organoboronate complexes: organotrifluoroborates, alkoxyorganoboronates or nitrogen-containing Lewis base adducts. The low reduction potentials of these compounds allows facile single-electron oxidation to generate non-stabilized alkyl radicals, including primary radicals, under mild conditions. The use of molecular oxygen is also a common way to activate boronic acids in photocatalytic reactions. The role of the oxygen relies on addition of the oxygen anion-radical formed in the photocatalytic cycle to the boron center affording the easily oxidizable boronate adduct. Amongst the variety of activation methods, the protocols avoiding the use of external Lewis base are especially valuable. This has been demonstrated in visible-light-mediated alkenylation of alkylboronic acids using alkenylsulfones as coupling partners. The radical species resulting from alkylboronic acid derivatives could be utilized in the formation of C–X or C–C bonds including enantioselective photoreactions. The application of boronic acids in the visible light-driven installation of side chains at dehydroalanine residues in proteins shows the increasing role of these compounds in future syntheses of complex natural products.

Lewis base catalyzed regioselective cyclization of allene ketones or α-methyl allene ketones with unsaturated pyrazolones.

A nitrogen-containing Lewis base catalyzed highly regioselective [4 + 2] cycloaddition of allene ketones or α-methyl allene ketones with unsaturated pyrazolones has been disclosed to give the corresponding tetrahydropyrano [2,3-c] pyrazoles in moderate to good yields under mild conditions. High regioselectivity, 100% atom-economy, broad substrate scope and good functional group tolerance are attractive features of this process and make it a practical and versatile transformation.

Divergent synthesis of hydropyridine derivatives via nitrogen-containing Lewis base mediated regioselective [4 + 2] cyclizations

A nitrogen-containing Lewis base mediated regioselective [4 + 2] cyclization strategy between allenic esters and α,β-unsaturated ketimines was discovered.

ChemInform Abstract: Lewis Base‐Catalyzed Reactions of Cyclopropenones: Novel Synthesis of Mono‐ or Multi‐Substituted Allenic Esters.

AbstractThis method yields allenes from cyclopropenones via ring‐opening.

Nucleophilic Lewis Base Dependent Addition Reactions of Allenoates with Trifluoromethylated Cyclic Ketimines

A detailed investigation on the different reactivity patterns shown by phosphorus- and nitrogen-containing Lewis base catalysts in the reactions of allenoates with cyclic trifluoromethyl ketimines was accomplished. With PPh3, [3 + 2] annulations proceeded smoothly to afford dihydropyrrole derivatives in excellent yields. Under the catalysis of DABCO, [2 + 2] annulations occurred, producing azetidine derivatives in good to high yields. However, in the presence of pyridine, α,α'-disubstituted allenoates were obtained in very high yields via aza-Morita-Baylis-Hillman reactions. These studies provide an opportunity for diverse synthesis of a variety of N-heterocyclic compounds from the same starting materials.

Lewis base-catalyzed reactions of cyclopropenones: novel synthesis of mono- or multi-substituted allenic esters

The reactions of cyclopropenones with nucleophiles (H2O or methanol) could be catalyzed by nitrogen-containing Lewis bases or phosphorus-containing Lewis bases, affording the corresponding mono- or multi-substituted allenic esters in moderate to excellent yields.

ChemInform Abstract: DABCO‐Mediated [4 + 2] Annulation of But‐3‐yn‐2‐one and Activated Ketones: Facile Preparation of 2,3‐Dihydropyran‐4‐one.

We found that nitrogen-containing Lewis base mediated [4+2] annulation of but-3-yn-2-one with activated ketones could proceed efficiently to give the corresponding 2,3-dihydropyran-4-ones in moderate to good yields under mild conditions. The substrate scope has been carefully examined. Moreover, a plausible reaction mechanism for the [4+2] annulation of but-3-yn-2-one with activated ketones mediated by DABCO has been proposed on the basis of previous literature and our own investigations.

ChemInform Abstract: Asymmetric Cyclization Reactions of Allenoates with Imines or α,β‐Unsaturated Ketones Catalyzed by Organocatalysts Derived from Cinchona Alkaloids.

AbstractReview: [60 refs.]

Asymmetric Cyclization Reactions of Allenoates with Imines or α,β‐Unsaturated Ketones Catalyzed by Organocatalysts Derived from Cinchona Alkaloids

Lewis base-catalyzed cyclization reactions of allenoates with electron-deficient olefins and imines have been demonstrated by the preparation of biologically active natural products and pharmaceutically interesting substances and have emerged as powerful synthetic tools in the rapid construction of cyclic molecular complexity. In contrast to phosphine-containing Lewis bases, nitrogen-containing Lewis base amines display markedly different reaction profiles; however, this area is not well-developed. Herein we summarize the recent progress in this emerging field and outline the challenges ahead.

Synthesis and characterization of nitrogen-containing Lewis base adducts of bis(O,O′-dialkylmonoselenophosphato)cobalt(II) complexes

The adducts of bis(O,O′-dialkylmonoselenophosphato)cobalt(II) complexes, Co{O(Se)P(OR)2}2(L)4 (where R = n-Pr, i-Pr; L = C5H5N, NC5H4Me-2, NC5H4Me-3), were synthesized by in situ reactions of CoCl2 · 6H2O, Lewis base, and NaO(Se)P(OR)2. The single crystal structure of Co{O(Se)P(OiPr)2}2(C5H5N)4 shows distorted octahedral geometry around cobalt(II) and monoselenophosphates are trans. The CoN4 forms a square plane. These bis(O,O′-dialkylmonoselenophosphato)cobalt(II) adducts were characterized by elemental analyses, spectroscopic techniques (UV-Vis, infrared, 1H and 31P), and magnetic moment measurements.

Binuclear copper(II) complexes with acyldihydrazones of benzenedicarboxylic acids with pyrrolidine or piperidine

The adducts of binuclear copper(II) complexes with acyldihydrazones formed by 1,3- or 1,4-benzenedicarboxylic acid and some nitrogen-containing Lewis bases (pyrrolidine, piperidine) were synthesized and studied. The structure of copper(II) complex with bis(salicylidene)hydrazone of terephthalic acid (H4L), [Cu2L(Pirr)4] · CH3OH, was determined by X-ray diffraction data. The crystals are monoclinic: a = 15.5142(7) A, b = 13.8784(6) A, c = 17.8873(8) A; β = 91.990(2)°, space group C2/c, Z = 4. The number of symmetrically independent reflections was 4269, R = 0.0303, Rw = 0.0827. The complex contains two equivalent copper atoms located at a 11.021 A is a tetragonal pyramid. EPR spectral features of the adducts were studied.

Phosphine- and Nitrogen-Containing Lewis Base Catalyzed Highly Regioselective and Geometric Selective Cyclization of Isatin Derived Electron-Deficient Alkenes with Ethyl 2,3-Butadienoate

An interesting phosphine-containing Lewis base catalyzed highly regioselective [3 + 2] cycloaddition and a novel nitrogen-containing Lewis base catalyzed highly geometric selective [4 + 2] cycloaddition of isatin derived α,β-unsaturated diesters with α-allenic ester have been disclosed to give the corresponding cyclic products in good to excellent yields under mild conditions. A plausible reaction mechanism has also been proposed on the basis of previous literature and our own investigation.

The rotational spectrum of the pyridine-hydrogen fluoride complex

Rotational spectra of two isotopomers of the pyridine-hydrogen fluoride complex were observed by using a pulsed-nozzle, FT microwave spectrometer. The constants A 0, B 0, C 0, Δ JK , Δ JK , δ J , δ K , x( 14 N) were determined for both isotopomers from analysis of the spectra. The complex is assigned C 2v symmetry, with the HF molecule lying along the C 2 axis of the C 5H 5N subunit. The distance r( Ntctdot;F) = 2.609(5) A ̊ was determined by fitting the rotational constants under the assumption of unperturbed monomer geometries, and the intermolecular stretching force constant k σ = 27.0(3) N m −1 was calculated from the distortion constant Δ J . The properties of a series of complexes Btctdot;HF, where B is a nitrogen-containing Lewis base, are compared.

Methylene-bridged Group 13-15 compounds, R2MCH2PPh2 (R = CH2CMe3, CH2SiMe3; M = Ga,In). Crystal structure of [(Me3CCH2)2InCH2PPh2]2.cntdot.C6D6, a molecule containing an In-C-P-In-C-P ring in a chair conformation

Abstract : A series of compounds of the type R2MCH2PPh2 (R = CH2CMe3, CH2SiMe3; M = Ga, In) have been prepared by metathetical reactions between the appropriate diorganometal halide and LiCH2PPH2 in pentane or Et2O at -78 C. All compounds were characterized by physical properties, partial elemental analyses (C, H), cryoscopic molecular weight measurements in benzene solution as well as IR, H NMR and P NMR spectroscopic data. All appropriate data support the existence of dimeric molecules. The monomeric species dimerize by apparent Lewis acid-base interactions. These interactions are sufficiently strong that the compounds do not form stable adducts with oxygen- or nitrogen-containing Lewis bases.

Europium dibenzoylmethide adducts

Europium(III) dibenzoylmethide forms solid adducts with a number of oxygen- and nitrogen-containing Lewis bases. The adducts all show the visible orange-red fluorescence characteristic of trivalent europium. However, the relative fluorescence intensities, as well as the number of resolved fluorescence bands and their wavelength maxima, show significant variation from compound to compound, suggesting that there is direct bonding between the europium ion and the base. The reflection spectra and heat stabilities of the solid complexes are also discussed.