Palladium-Catalyzed Benzylation of Unprotected Anthranilic Acids with Benzyl Alcohols in Water

Ubiquitous Role of Phosphine-Based Water-Soluble Ligand in Promoting Catalytic Reactions in Water

Catalysis has been at the forefront of the developments that has revolutionised synthesis and provided the impetus in the discovery of platform technologies for efficient C-C or C-X bond formation. Current environmental situation however, demands a change in strategy with catalysis being promoted more in solvents that are benign (Water) and for that the development of hydrophilic ligands (especially phosphines) is a necessity which could promote catalytic reactions in water, allow recyclability of the catalytic solutions and make it possible to isolate products using column-free techniques that involve lesser usage of hazardous organic solvents. In this review, we therefore critically analyse such catalytic processes providing examples that do follow the above-mentioned parameter.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Direct substitution of benzylic alcohols with electron-deficient benzenethiols via π-benzylpalladium(ii) in water

An efficient and environmentally benign method for the direct nucleophilic substitution of benzylic alcohols with electron-deficient benzenethiols in water is developed. This strategy is an attractive atom-economical process, which affords the desired products along with water as the sole co-product.

Benzoyl methyl phosphate as an efficient reagent for the selective monobenzoylation of N-Bz-FTY720

A novel and efficient method for the selective monobenzoylation of N-Bz-FTY720 with benzoyl methyl phosphate (BMP) promoted by Zn(OAc)₂ and Cs₂CO₃ was developed. Benzoyl methyl phosphate plays an important role as a biomimetic acylating agent for the monobenzoylation of 1,3-diols.

Mercaptobenzoic acid-palladium(0) complexes as active catalysts for S-benzylation with benzylic alcohols via (η3-benzyl)palladium(ii) cations in water

Mercaptobenzoic acid-palladium(0) complexes show high catalytic activity for S-benzylation with benzylic alcohols via the (η³-benzyl)palladium(ii) cation in water. The catalytic system can be performed using only 2.5 mol% Pd₂(dba)₃ without the phosphine ligand or other additives.

[Development of unprotected syntheses in aqueous media]

Introduction of carbon side chain at C(3)-position of indole ring was accomplished by using Pd-catalyzed allylation and vinylation. The selective vinylation at C(3)-position of 4-bromoindole was applied to the synthesis of optically active 4-bromotryptophan derivatives, which was used as a starting material for the synthesis of several optically active ergot alkaloids, which were clavicipitic acids, chanoclavine-I, costacalvine, and 1,1-dimethylallyltryptophan (DMAT). The three-step synthesis of optically active clavicipitic acids were accomplished without using a protecting group starting from 4-bromoindole and dl-serine. Some new synthetic reactions using unprotected amino acids were developed. Those were the biomimetic synthesis of tryptophan, the bromination of free aromatic amino acids, and the Pd-catalyzed N-allylation of free amino acids with allylic alcohol in aqueous media. Unique reactivity of π-allyl palladium complex or η3-(benzyl)palladium complex in aqueous media was found through Pd-catalyzed reaction of anthranilic acid, 2-aminobenzamide, and indole with allylic alcohols or benzyl alcohols, respectively.