Copper-catalyzed radical/radical cross-coupling of ketoxime carboxylates with 4-hydroxycoumarins: A novel synthesis of furo[3,2-c]-coumarins

A novel and efficient strategy for the synthesis of furo[3,2-c]coumarins has been developed via copper-catalyzed radical/radical cross-coupling of ketoxime carboxylates with 4-hydroxycoumarins. This redox-neutral reaction allows smooth and selective synthesis of 2-substituted, 3-substituted, 2,3-disubstituted and 2,3-fused polycyclic furo[3,2-c]coumarins.     

Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy : Part II. Integrated molar absorptivities of alkyl carboxylates

A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO⁻], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm⁻¹. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol⁻¹ cm⁻¹, and the integrated molar absorptivity is 2.95 ± 0.08 × 10⁴ l mol⁻¹ cm⁻² (n = 15 compounds, 0.1 M ≤ [COO⁻] ≤ 1.5 M). The [COO⁻] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO⁻ groups.     

Zinc-metal promoted selective α-haloacylation and gem-bisacylation of alkyl aldehydes in the presence of chlorotrimethylsilane

Treatment of a mixture of alkyl aldehydes (1) with acid chlorides (2) in the presence of zinc metal powder and a catalytic amount of chlorotrimethylsilane (TMSCl) in dichloromethane brought about highly facile and effective coupling to give selectively the corresponding α-haloacylation and gem-bisacylation products, α-haloalkyl carboxylates and 1,1-dicarboxylates (acylals), in good to excellent yields.     

Ring opening reactions of pyromellitic dianhydride for the synthesis of first row transition metal dicarboxylate complexes

The ring opening reaction of pyromellitic dianhydride by methanol is an effective method to prepare first row transition metal dicarboxylate complexes. The reactions of different first row transition metal salts with pyromellitic dianhydride in the presence of nitrogen donating bidentate ligands such as 1,10-phenanthroline and 2,2′-bipyridine gives different compositions depending on the ligand and the metal salts used. For example, the reaction of nickel(II) acetate with pyromellitic dianhydride in the presence of 1,10-phenanthroline results in the formation of a carboxylato bridged nickel(II) metallacycle through the ring opening reaction of pyromellitic dianhydride (PAH) at the 1 and 3-positions, whereas a mononuclear tetra-aqua 2,2′-bipyridine nickel(II) complex is formed in a similar reaction of nickel(II) acetate through ring opening at the 1,4-position of PAH. Mononuclear cobalt(II) dicarboxylate complexes are formed from the ring opening reaction of pyromellitic dianhydride in methanol in the presence of the nitrogen donor ligands 1,10-phenanthroline or 2,2′-bipyridine. Copper(II) chloride on reaction with PAH and 2,2′-bipyridine gives a mononuclear complex via ring opening at the 1 and 4-positions; having chlorides inside and outside the coordination sphere. Whereas, the reaction of copper(II)acetate gives dinuclear copper complexes having a monodentate carboxylato bridge arising from the carboxylato groups at the 1 and 4-positions on the aromatic ring. The crystal structures of all the complexes have been determined.     

Transformations of Methyl 2‐[(E)‐2‐(Dimethylamino)‐1‐(methoxycarbonyl)ethenyl]‐1‐methyl‐1H‐indole‐3‐carboxylate

A simple and efficient synthesis of novel 2‐heteroaryl‐substituted 1H‐indole‐2‐carboxylates and γ‐carbolines, compounds 1 – 3 , from methyl 2‐(2‐methoxy‐2‐oxoethyl)‐1‐methyl‐1H‐indole‐3‐carboxylate ( 4 ) by the enaminone methodology is presented.     

Carboxylate Catalyzed Isomerization of β,γ-Unsaturated N-Acetylcysteamine Thioesters**

We demonstrate herein the capacity of simple carboxylate salts – tetrametylammonium and tetramethylguanidinium pivalate – to act as catalysts in the isomerization of β,γ-unsaturated thioesters to α,β-unsaturated thioesters. The carboxylate catalysts gave reaction rates comparable to those obtained with DBU, but with fewer side reactions. The reaction exhibits a normal secondary kinetic isotope effect (k_1H/k_1D=1.065±0.026) with a β,γ-deuterated substrate. Computational analysis of the mechanism provides a similar value (k_1H/k_1D=1.05) with a mechanism where γ-reprotonation of the enolate intermediate is rate determining.     

Relaxation effects in the Mössbauer spectra of iron complexes with fatty acids

Six new oxo trinuclear iron(III) complexes of the type [Fe₃O(R–COO)₆(H₂O)₃] X, where X= or Cl^– and R=C₅, C₇, C₈, C₉ were synthesized and investigated by Infra Red, Mössbauer Spectroscopy and magnetic measurements. The data pointed to a high spin state (S=5/2) for iron and for antiferromagnetic interactions. The asymmetrical shape of the Mössbauer doublet and its temperature dependence was treated using the Blume relaxation model. The relaxation process is influenced by both X and R components.