Water-More Than Just a Green Solvent: A Stereoselective One-Pot Access to All-Chiral Tetrahydronaphthalenes in Aqueous Media

Cu(OAc)2-catalyzed three-component cycloaddition of malonates, nitrosoarenes and alkenes: access to isoxazolidines

The Cu(OAc)₂-catalyzed one-pot three-component cycloaddition of malonates, nitrosoarenes and alkenes is described. A wide range of isoxazolidines could be obtained in moderate to excellent yields via this method. Mechanistic investigations indicated that the key step in this catalytic system is the straightforward formation of nitrone intermediates through the Cu(OAc)₂-catalyzed reaction of malonates with nitrosoarenes.

Hydrazones as Substrates in the Synthesis of Isoxazolidines via a KOH-Promoted One-Pot Three-Component Cycloaddition with Nitroso Compounds and Olefins

Hydrazones have been employed as the starting materials in a KOH-mediated one-pot three-component cycloaddition with readily accessible nitroso compounds and olefins to construct various isoxazolidines. Compared with diazo compounds as starting materials, this methodology could afford a wider range of products in good to excellent yields and diastereoselectivities for most substrates, and hydrazones are cheaper, more accessible, and safer substrates. The experimental study shows that the choice of suitable hydrazones is crucial.

NBS/DBU-Promoted One-Pot Three-Component Cycloaddition of Malonic Acid Derivatives, Nitrosoarenes, and Alkenes: Synthesis of Isoxazolidines

A general DBU-mediated one-pot three-component cycloaddition reaction of easily accessible malonic acid derivatives, nitrosoarenes, and alkenes has been successfully established with the aid of NBS to provide direct access to highly functionalized isoxazolidine derivatives with generally good to excellent yields, broad functional group tolerance, and excellent regio- and diastereo-selectivities under mild conditions. The mechanism study shows that the NBS-mediated formation of bromomalonic acid derivatives from malonic acid derivatives and DBU-promoted synthesis of nitrone intermediates via the reaction of bromomalonic acid derivatives with nitrosoarenes are key steps.

N-Alkyl nitrones as substrates for access to N-aryl isoxazolidines via a catalyst-free one-pot three-component reaction with nitroso compounds and olefins

N-Alkyl nitrones are used as starting materials to construct N-aryl isoxazolidines, instead of N-alkyl isoxazolidines or N–H 1,3-oxazinanes via a catalyst-free one-pot three-component reaction with nitrosoarenes and olefins.

Synthesis of isoxazolidines via catalyst-free one-pot three-component cycloaddition of sulfoxonium ylides, nitrosoarenes and alkenes

A general and practical strategy for the construction of various keto-substituted isoxazolidines via one-pot three-component reaction of easily accessible, safer and more stable sulfoxonium ylides, nitrosoarenes and olefins is described.

Green Asymmetric Organocatalysis

Asymmetric organocatalysis is becoming one of the main tools for the synthesis of chiral compounds that are needed as medicines, crop protection agents, and other bioactive molecules. It can be effectively combined with various green chemistry methodologies. Intensification techniques, such as ball milling, flow, high pressure, or light, bring not only higher yields, faster reactions, and easier product isolation, but also new reactivities. More sustainable reaction media, such as ionic liquids, deep eutectic solvents, green solvent alternatives, and water, also considerably enhance the sustainability profile of many organocatalytic reactions.

Greener Synthesis of Nitrogen-Containing Heterocycles in Water, PEG, and Bio-Based Solvents

The solvents used in chemistry are a fundamental element of the environmental performance of processes in corporate and academic laboratories. Their influence on costs, health safety, and nature cannot be neglected. Quantitatively, solvents are the most abundant constituents of chemical transformations; therefore, acting on solvents and replacing standard solvents with safer products can have a great ecological impact. However, not all green solvents are suitable for the wide scope of organic chemistry reactions. A second point to consider is that 50% of pharmaceutical drugs are nitrogen heterocycles compounds. It therefore appeared important to provide an overview of the more ecological methodologies for synthesizing this class of compounds. In this review, all publications since 2000 that describe green reactions leading to the formation of nitrogen heterocycles using safe solvents were considered. We chose water, PEG, and bio-based solvents for their negligible toxicity. The synthesis of five-, six-, and seven-membered aromatic nitrogen heterocycles using green reactions reported in the literature to date is described.

The smallest organocatalyst in highly enantioselective direct aldol reaction in wet solvent-free conditions

The catalytic efficacy of the smallest organocatalyst, l-proline hydrazide, prepared from a cheaply available natural amino acid, such as l-proline, was studied for the direct asymmetric aldol reaction of various ketones with aromatic aldehydes at room temperature in the presence of several acid additives.

Green chemistry oriented organic synthesis in water

The use of water as solvent features many benefits such as improving reactivities and selectivities, simplifying the workup procedures, enabling the recycling of the catalyst and allowing mild reaction conditions and protecting-group free synthesis in addition to being benign itself. In addition, exploring organic chemistry in water can lead to uncommon reactivities and selectivities complementing the organic chemists' synthetic toolbox in organic solvents. Studying chemistry in water also allows insight to be gained into Nature's way of chemical synthesis. However, using water as solvent is not always green. This tutorial review briefly discusses organic synthesis in water with a Green Chemistry perspective.

Diastereo- and enantioselective synthesis of oxazine and oxazolidine derivatives with a chiral quaternary carbon center under multifunctional catalysis

An easy one-pot, multistep cascade reaction which could afford a series of substituted benzo[d]pyrido[2,1-b]oxazolidine and [1,3]oxazine derivatives in a highly enantio- (up to 98% ee) and diastereoselective (4:1 to >20:1 dr) manner with generally good to excellent yields (up to 99%) has been developed. This well designed strategy could be applied to a wide scope of substrates under mild conditions with simple operations.

Highly chemoselective Baylis-Hillman and aldol reactions of 2H-thiopyran-4(3H)-one using tertiary amine catalysts in aqueous media

For the first time, the Baylis-Hillman (BH) reaction of 2H-thiopyran-4(3H)-one is investigated, and surprisingly, the reaction of 2H-thiopyran-4(3H)-one with aldehydes in the presence of different tertiary amines shows excellent chemo- and regioselectivity in water. At room temperature, DBU affords BH adducts, but with DABCO, aldol products were obtained. In the case of DABCO, Et(3)N, or DMAP, domino aldol-rearrangement reactions occurred at 45-50 °C.