Melamine and Melamine-Formaldehyde Polymers as Ligands for Palladium and Application to Suzuki–Miyaura Cross-Coupling Reactions in Sustainable Solvents

Abstract

The Suzuki-Miyaura cross-coupling reaction is a foundation stone of modern organic synthesis, as evidenced by its widespread use in the preparation of pharmaceuticals, agrochemicals, polymers, and other functional materials. With the prevalence of this venerable reaction in industrial synthesis, it is prudent to ensure its application adheres to the tenets of green chemistry. The introduction of cross-coupling catalysts that are active in sustainable solvents is therefore an important endeavor. In this report, a melamine-palladium complex is introduced as a versatile catalyst for the Suzuki-Miyaura cross-coupling reaction. This catalyst is soluble and active in both water and the renewable organic solvent ethyl lactate. The melamine-palladium catalyst can also be cross-linked by reaction with formaldehyde to generate an insoluble polymeric catalyst that can be recovered after the cross-coupling. The melamine-palladium system is inexpensive, easy to handle, bench-stable, and effective in catalysis in the presence of a variety of impurities (high cross-coupling yields were obtained in reactions run in unfiltered river water to illustrate this final point). Additionally, investigations reported herein revealed an intriguing relationship between catalytic efficiency and the base employed in the cross-coupling reaction. Implications for the mechanism of transmetalation in aqueous Suzuki-Miyaura cross-coupling reaction are discussed.

Catalyst Free Synthesis of Bis(Indolyl)Methanes and 3,3‐Bis(Indolyl)oxindoles in Aqueous Ethyl Lactate

“…In recent years, ethyl lactate (EL) has been introduced as a possible environmentally safe solvent in organic synthesis due its intrinsic characteristics such as low price, less toxicity, good biodegradability, high stability as well as solubility to both water and organic compounds . Literature survey shows that EL has been used in some organic transformations such as coupling reactions, cycloaddtion reaction, multi‐component reactions, light induced synthesis, and stereoselective synthesis . Therefore, it is worth emphasizing that the development of an efficient and rapid synthetic route for the preparation of biologically and drug active molecules by combining the synthetic efficiency of ultrasonic‐assisted organic reactions and advantages of EL as reaction medium under catalyst free conditions is highly desirable and deserves significant attention.…”

Acetamidoarenediazonium Salts: Opportunities for Multiple Arene Functionali­zation

“…4‐Phenylacetanilide ( p ‐27a): 89 Compounds p ‐ 2a (100 mg, 0.40 mmol) and 26a (110 mg, 0.60 mmol) were converted into p ‐ 27a (74 mg, 0.35 mmol, 89 %) by the General Procedure: colourless solid, m.p. 163 °C.…”

The Suzuki–Miyaura Cross-Coupling as a Versatile Tool for Peptide Diversification and Cyclization

“…Recent reviews on sustainable Suzuki-Miyaura reactions in aqueous media discuss the use of recoverable catalysts, yet these are limited to non-peptidic substrates [11,138,182]. In this respect, several recyclable catalysts [183][184][185][186][187][188][189][190], including silica-or polymer-supported catalysts and magnetically recoverable catalysts, are reported for biaryl formation and could potentially be implemented for transformations of peptide substrates.…”