Addition of trifluoromethyltrimethylsilane to acyl phosphonates: synthesis of TMS-protected 1-alkyl-1-trifluoromethyl-1-hydroxyphosphonates and 1-aryldifluoroethenyl phosphates

Addition reactions of nucleophilic CF3TMS to acyl phosphonates were investigated. Various acyl phosphonates reacted readily with CF3TMS in the presence of K2CO3 in DMF at rt to give 1-alkyl-2,2,2-trifluoro-1-trimethylsilyloxyethylphosphonate in 70-90% yields. When benzoyl phosphonates were used as starting material, after addition of CF3, the formed alcoholate undergoes phosphonate-phosphate rearrangement to form the acyl anion, followed by elimination of F- to give 1-aryldifluoroethenyl phosphates in 87-97% yields. As a representative example, vinylphosphate 6a was converted into 2,2-difluoro-1-phenylethanone 7 with 6 N HCl/EtOH/reflux or CAN/NaOH/MeOH/0 degrees C in 82-90% yields.     

Upper rim-functionalized calix[4]arene-based l-proline as organocatalyst for direct asymmetric aldol reactions in water and organic media

The synthesis of upper rim-functionalized calix[4]arene-based l-proline was described, and its catalytic efficiency as organocatalyst for the enantioselective aldol reaction in water was investigated. The results showed that the nature of the hydrophobic cavity of calixarene is critical for catalytic activity in water. The products of the reaction between various ketones and aldehydes with anti-configuration were obtained in high yields (up to 94%) with high diastereo- (up to 95:5 dr) and enantioselectivities (up to 80% ee).     

L-proline derivatives based on a calix[4]arene scaffold as chiral organocatalysts for the direct asymmetric aldol reaction in water

Abstract

A new series of water-compatible proline catalysts (4–6) derived from calixarene bearing a hydrophobic nature have been synthesised. It was found that the compound 4 was a highly efficient organocatalyst for aldol reactions occurred in the water. Under optimised reaction conditions, high yields (up to 82%), good enantioselectivities (ee up to 81%) and high diastereoselectivities (dr up to 91:9) were obtained.     

Synthesis,characterization, biological activity,and DFT-reactivity assessment of Mn(II), Co(II), and Cu(II) complexes of a new N2O tridentate Schiff base

Russian Journal of General Chemistry - Three new homoleptic Schiff base: metal(II) complexes, bis{2-[(pyridin-2-yl) methylene-amino] naphthoxometal(II)} [M(npa)2], (M = Mn(II) (1), Co(II) (2),...     

Nonlinear effects in proline–thiourea host–guest complex catalyzed aldol reactions in nonpolar solvents

An aldol reaction catalyzed by a proline–thiourea host–guest complex in a nonpolar solvent shows excellent nonlinear effects. This proline–thiourea system has the ability to form a hydrogen-bonding network. The enantiomeric excess of proline in a solution can be significantly enhanced by its incorporation with a urea molecule into its solid racemate. This suggests a general and facile route to homochirality, which may be involved in the origin of chirality on earth.     

Generation of acyl anion equivalents from acylphosphonates via phosphonate-phosphate rearrangement: a highly practical method for cross-benzoin reaction

[reactions: see text] Acylphosphonates are potent acyl anion precursors that generate acyl anion equivalents under the promotion of cyanide anion via phosphonate-phosphate rearrangement. These anions readily react with aldehydes to provide cross-benzoin products. In this way it is possible to synthesize a variety of aromatic-aromatic, aromatic-aliphatic, and aliphatic-aromatic benzoins. Moreover the reaction of benzoylphosphonate with potent electrophile 2,2,2-trifluoroacetophenone provided the corresponding aldehyde-ketone coupling product in high yield.     

Preparation of calix[4]arene-embedded polysulphone membranes,and utilisation of its Cr(VI) transport efficiency

In this study, a tetramine-substituted calix[4]arene derivative, which was synthesised from calix[4]arene by treatment with dimethylamine in one step via Mannich reaction, was used to fabricate a new calix[4]arene-embedded polysulphone membrane (calix@membrane). Its structure and surface morphology were determined using thermogravimetric analysis and scanning electron microscopy, and elemental analysis techniques. Moreover, a Donnan dialysis system was employed to investigate Cr(VI) transport efficacy of calix@membrane at different pH values. Results showed that calix@membrane represented a promising transport capability for HCr₂O₇^? due to their efficient complexation behaviour.     

Self-assembly of organocatalysts for the enantioselective Michael addition of aldehydes to nitroalkenes

A proline–thiourea self-assembled organocatalyst is described as a good catalyst for the enantioselective nitro-Michael addition of aldehydes to nitroalkenes. The reaction is efficient with 5% of the thiourea, to give moderate to good enantioselectivity (up to 76% ee). High syn-selectivity was obtained with both branched and unbranched aliphatic aldehydes. This is the first example of self-assembly of organocatalysts with an achiral additive in a Michael addition wherein aldehydes are utilized as donors.     

Direct enantioselective aldol reactions catalyzed by calix[4]arene-based l-proline derivatives in the water

Two novel p-tert-butylcalix[4]arene-based chiral organocatalysts derived from l-proline have been developed to catalyze direct aldol reactions between cyclohexanone and aromatic aldehydes in water. Under the optimal conditions, high yields (up to 95%), enantioselectivities (up to 90%), and moderate diastereoselectivities (up to 65:35) were obtained. Considering the catalytic inefficiency of sole proline for the aldol reaction in water, these results clearly display the enormous effect of the hydrophobic part of calix[4]arene of compound A.