A Green Chemoenzymatic Process for the Synthesis of Azoxybenzenes

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.

Direct photochemical route to azoxybenzenes via nitroarene homocoupling

We report on a direct photochemical method for the one-pot, catalyst- and additive-free synthesis of azoxybenzene and substituted azoxy derivatives from nitrobenzene building blocks. This reaction is conducted at room temperature and under air, and can be applied to substrates with a wide range of substituents. Yields of products derived from para- and meta-substituted nitrobenzenes are typically good, while sterically encumbered ortho-substituted substrates are not as fruitful. Photochemical Wallach rearrangement of generated azoxybenzenes to ortho-hydroxyazoxybenzenes was observed in some cases, most markedly in selected ortho-halogenated nitrobenzenes. Overall, this method provides an efficient, green pathway to highly value-added azoxybenzene products.

A Direct Method for the Efficient Synthesis of Hydroxyalkyl-Containing Azoxybenzenes

Reaction of nitrobenzyl alcohol with glucose (200 mol%) in the presence of NaOH in water-ethanol medium gave 1,2-bis(4-(hydroxymethyl)phenyl)diazene oxide, 1,2-bis(2-(hydroxymethyl)phenyl)diazene oxide and 1,2-bis(4-(1-hydroxyethyl)phenyl)diazene oxide in 76%, 76% and 72% yields, respectively.

Synthesis of substituted 2H-chromenes catalyzed by lipase immobilized on magnetic multiwalled carbon nanotubes

Porcine pancreas lipase (PPL) was immobilized on magnetic multiwalled carbon nanotubes successfully for the synthesis of substituted 2H-chromenes. The catalytic activity of immobilized PPL was much higher than that of free PPL. Effects of reaction medium, temperature, and enzyme dosage were also investigated. Under optimum reaction conditions (acetylacetone (1 mmol), salicylaldehyde (1 equivalent), methanol (10 equivalent), and immobilized PPL (protein content: 30 mg; 65 °C; DMF 5 mL; 5 H), the immobilized PPL showed an excellent catalytic performance on the synthesis of substituted 2H-chromenes. Moreover, the immobilized PPL exhibited satisfactory thermostability, operational simplicity, and reusability in this reaction.

The influence of the isocyanoesters structure on the course of enzymatic Ugi reactions

The impact of isocyanoesters structure on enzymatic three-component Ugi reactions course has been determined. The significant promiscuous ability of enzyme in Ugi-type reaction switching between four (U-4CR) and three (U-3CR) components reactions depending on the size of used isocyanoester. The application of short-chain cyanoesters up to isocyanpropionate leading to product of three component reaction exclusively while longer isocyanobutyrate gives only the product of four component reaction. The limitation of studied enzymatic Ugi reaction is a substrate selectivity of lipases.

Novel chemoenzymatic oxidation of amines into oximes based on hydrolase-catalysed peracid formation

The efficient transformation of benzylamines into the corresponding oximes has been described by means of a chemoenzymatic process.