Syntheses Of Guanidine, Guanidinium Salts And Their Applications On Michael Addition Reaction

The 1, 4-conjungate addition (Michael addition) reaction is one of the most convenient and efficient methods for the construction of carbon-carbon bond and has been widely applied in organic synthesis. The catalysts traditionally used for Michael addition of active methylene compounds toα,β-unsaturated compounds include strong bases or Lewis acids, which usually result in undesirable side reactions. Recently, extensive work has focused on the investigation of catalysts which would result in mild reaction conditions, high selectivity and tolerating a wide range of nucleophilic substrates. Thus, a number of suitable catalysts such as rubidium salt of L-proline, K2CO3, Al2O3, [bmIm]BF4and [bmIm]OH have been developed over the past few years.During the last decade, air- and water- stable room temperature ionic liquids (ILs) have emerged as a green alternative to volatile and hazardous organic solvents. ILs usually consists of organic cations, such as imidazolium or pyridium species and anions counterparts, such as, AlX4-, BF4-, PF6-, CF3SO3- or (CF3SO3)2N- etc. Moreover, ILs is readily prepared and the properties could be easily adjusted by changing the anion or the alkyl groups attached to the cation. The modification of the structures of the cations or anions of ILs can result in some unique properties, which can alter the outcomes of various reactions. To date, ILs has been recognized as an efficient and recyclable reaction media for a variety of important reactions. Recently, they have been proved to be efficient medium for Michael addition reaction. In the past several years, our group has successfully used tetramethylguanidium ionic liquids as dual solvent-catalyst in oxidation of alcohols, the nucleophilic substitution of alkyl halides, Heck reaction and Knoevenagel condensation reaction. Herein, tetramethylguanidium lactate ionic liquid used as dual solvent-catalyst for Michael additionsis reported and its catalytic activity for Michael addition is also investigated.Tetramethylguanidium lactate ionic liquid is a kind of versatile media used in organic synthesis. This work mainly based on the following three aspects:1. In this paper, we designed and synthesized a series of guanidinium halides and guanidinium ionic liquids (GRTILs) to study their properties and applications.2. A facile and efficient Michael addition reacion of active methylene compounds to chalcones and nitroalkenes catalyzed by guanidinium lactate ionic liquid is developed. The simple procedure, very mild conditions, quantitative yields and especially that the IL can be recovered and reused without any catalytic activity loss make this protocol much attractive for academic research and practical applications.3. A Catalyst-free, facile and efficient Michael addition reaction of active methylene compounds as well as nitromethane to chalcones catalyzed by tetramethyl- guanidium lactate ionic liquid is developed. A range of chalcones with active methylene compounds and nitromethane have been converted smoothly to the corresponding products in high yields. The simple procedure, very mild conditions, high yields and especially that the IL can be recovered and reused without any catalytic activity loss make this protocol much attractive for academic research and practical applications.Based on the experimental results, it can be conjectured that the base acidity of the cation may act as main activie site for the activation of epoxide. At present, we are taking on other application of guanidinium salts and guanidinium ionic liquids.