Lipase-Catalyzed Phospha-Michael Addition Reactions under Mild Conditions

Organophosphorus compounds are the core structure of many active natural products. The synthesis of these compounds is generally achieved by metal catalysis requiring specifically functionalized substrates or harsh conditions. Herein, we disclose the phospha-Michael addition reaction of biphenyphosphine oxide with various substituted β-nitrostyrenes or benzylidene malononitriles. This biocatalytic strategy provides a direct route for the synthesis of C-P bonds with good functional group compatibility and simple and practical operation. Under the optimal conditions (styrene (0.5 mmol), biphenyphosphine oxide (0.5 mmol), Novozym 435 (300 U), and EtOH (1 mL)), lipase leads to the formation of organophosphorus compounds in yields up to 94% at room temperature. Furthermore, we confirm the role of the catalytic triad of lipase in this phospha-Michael addition reaction. This new biocatalytic system will have broad applications in organic synthesis.

Low-Symmetry β-Diketimine Aryloxide Rare-Earth Complexes: Flexible, Reactive, and Selective

We report the synthesis, characterization, and reactivity of a new low-symmetry β-diketimine featuring a pendant amino(methyl)phenol donor and its corresponding heteroleptic rare-earth (RE) complexes. This includes the first structurally characterized examples of alcoholysis and insertion from an isolated RE^III amide in a β-diketimine framework. The flexible methylene linkage leads to RE^III complexes with tunable dynamic solution behavior that defines their stoichiometric and catalytic reactivity. The addition of a strong neutral donor ligand, tricyclohexylphosphine oxide, suppresses a prevalent catalyst degradation pathway (base-promoted elimination) and dramatically enhances the catalyst performance in the stereospecific ring-opening polymerization of rac-β-butyrolactone. Our results further demonstrate the importance of ligand reorganization in the stoichiometric and catalytic activity of RE^III ions.

The Syntheses, Characterization and Crystal Structures of a Series of Heterocyclic β-Diketones and Their Isoxazole Compounds

BACKGROUND

In the field of coordination chemistry, the introduction of heterocyclic substituents into the structure of β-diketone enables ligand to produce multiple coordination sites. The adoption of small steric oxime group into the structure of heterocyclic β-diketone by Schiff-base condensation will further increase coordination sites and facilitate the generation of polynuclear structures.

OBJECTIVE

A series of β-diketones (2a-2c) containing different heterocycles such as pyridine, thiophene and furan and their corresponding isoxazole compounds (3a-3c) were synthesized.

MATERIALS AND METHODS

The Claisen condensations were investigated in a solvent-free rheological phase system at room temperature to obtain heterocyclic β-diketones 2a-2c, which further reacted with hydroxylamine hydrochloride to obtain heterocyclic isoxazoles 3a-3c. All these compounds were well characterized by EA, IR, 1H NMR and X-ray crystal diffraction to confirm the structures. Synthetic mechanisms of compounds and the effects of different heterocycles on reactivity were discussed deeply.

RESULTS

1H NMR indicated that these β-diketones do not exist as a total diketonic form but an equilibration between diketone and enol forms in CDCl3 solvent, in which the enol form accounts for 98.0% in 2a, 94.3% in 2b, 95.5% in 2c. While the crystal structures of 2a-2c showed that the reaction allows to isolate diketones in solid state. Crystal structures of 3a-3c showed that the neutral β-ketone oximes resonate and cyclize to form the target heterocyclic isoxazoles.

CONCLUSION

SN1 nucleophilic substitution mechanism of Claisen ketoester condensation was proposed for the syntheses of 2a-2c, and SN1 single molecule nucleophilic substitution reaction mechanism was put forward for 3a-3c.

Catalyst-free hydrophosphination of alkenes in presence of 2-methyltetrahydrofuran: a green and easy access to a wide range of tertiary phosphines

A hydrophosphination reaction that is free of base, acid and catalyst, using only 2-methyltetrahydrofuran as additive has been performed. A new family of mono-, di-, tri- and tetra-phosphines compounds are obtained in good to excellent yields by adding diphenylphosphine to alkenes, mono- and polyfunctional acrylics (based on acrylate and methacrylate motifs) and acrylamide substrates. Addition of four equivalent of bio-mass derived 2-MeTHF into the reaction media improves both conversion and time of the reaction and reduces the sensitivity of the reactants over oxidation. This simple, straightforward and atom-economic method respects the principles of Green Chemistry. Furthermore, in each case this transformation shows an exclusive regioselectivity towards the anti-Markovnikov products.

A hydrophosphination reaction that is free of base, acid and catalyst, using only 2-methyltetrahydrofuran as additive has been performed.

Variable coordination of carbazolyl-bis(tetrazole) ligands in lanthanide chemistry

Lanthanide complexes of 1,8-bis(2′-isopropyltetrazo-5′-yl)-3,6-di-tert-butylcarbazolide adopt geometries that include planar, buckled and tetrazolyl-bridged tridentate, as well as bidentate, bonding modes.