No abstract

No abstract

No abstract

a b s t r a c tThe first successful Pd(OAc) 2 , N-donor ligand and base mediated Heck coupling reaction of aryl halides and alkenes in water is described. The corresponding Heck products were obtained in good to excellent yields.The palladium-catalyzed Heck reaction 1 between aryl halides and alkenes is a versatile method for carbon-carbon bond formation in organic synthesis. 2 To minimize the adverse impact of organic solvents on the environment, recent efforts have been directed towards using aqueous solvents for chemical reactions. 3 Organic reactions in water or aqueous media have attracted great interest. 4 With tightened regulatory pressure focusing on organic solvents, the search for alternatives is of increasing importance. In this respect, the development of water-tolerant catalysts has rapidly become an area of intense research. There have been several reports concerning the Heck reaction in water; however, in most cases, high temperatures were required. 5,6 These findings prompted us to investigate the Heck reaction in aqueous media, in continuation of our interest in developing novel synthetic methodologies, particularly carbon-carbon bond forming reactions.Palladium-catalyzed Heck reactions between aryl halides and alkenes continue to attract attention within the chemistry community because of the versatility of the reaction and the potential of the products formed. 7 The area that has perhaps received most research effort is the development of new catalysts and ligands for Heck coupling reactions and the use of these catalyst systems in, for example, natural product synthesis. Recently, novel phosphine-free ligands 8 and hydrazone 9 were used as catalysts for the Heck reaction. In addition, Li and Wang reported triethanolamine as a ligand as well as base for Heck reactions. 10 As part of an ongoing project, 11 we herein disclose a novel protocol for the Heck reaction using N-donor ligand (1a) as a ligand and base, which makes use of milder conditions compared to those reported, Scheme 1. The method is simple and affords good to excellent yields. N-donor ligand 1a was synthesized by reaction of the corresponding primary amine (2-(pyridine-3-yl)ethyl amine) with sodium vinylsulfonate in water using a literature procedure. 12 We initially studied the effect of 1a as a base along with other bases in different solvents for Heck reactions, and our results are summarized in Table 1.We employed the coupling reaction of iodobenzene with methyl acrylate as a model reaction to study the effect of base on the reaction. The reactions were carried out using K 2 CO 3 (1 equiv) as base and ligand 1a (0.25 equiv, which is highly water soluble) in the presence of 0.3 mol % Pd(OAc) 2 at room temperature. The reaction in pure DMF afforded 3-phenyl acrylic acid methyl ester in very low yield after 4 h (Table 1, entry 1). If we kept the catalyst, base and ligand 1a constant and used different solvents such as DME, NMP, NMP-water and DMF-water, the desired product was obtained in 40-61% yields (Table 1, entries 2-5). Howe...

No abstract