Organic cyclic carbonate synthesis

The above studies [8-10] strongly indicate the participation of silanol groups as acid sites in the amine-catalyzed reactions. The synergistic catalysis of immobilized organic bases and silanol groups has been highlighted by the cyclic carbonate synthesis from carbon dioxide and epoxide. Acid-base dual activation mechanism of the cyclic carbonate synthesis is widely accepted. Sakakura and coworkers [11] reported silica-supported phosphonium salts as highly active catalysts for the cyclic carbonate synthesis. The results for propylene carbonate synthesis are summarized... 

Silica gel-based catalytic systems have been described as efficient promoters for a number of organic reactions.28 Illustrative examples include the oxidative cleavage of double bonds catalyzed by silica-supported KM11O4,29 reaction of epoxides with lithium halides to give /i-halohydrins performed on silica gel,30 selective deprotection of terf-butyldimethylsilyl ethers catalyzed by silica gel-supported phosphomolybdic acid (PMA),31 and synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts.32... 

The synthesis of enantiomerically pure compounds is the challenging problem for organic chemists. The synthesis becomes obsolete if the intermediates produce racemic mixtures. The problem is particularly acute when the asymmetric centers do not reside in a rigid cyclic or polycyclic framework. To be able to carry out efficient syntheses of complex molecules, chemists have to control the sense of chirality at each chiral center as it is introduced in the course of synthesis. Monoalkyl- or dialkyl-boranes exhibit a remarkable chemo-, stereo-, and regioselectivity for the hydroboration of unsaturated compounds. This property, coupled with the capability for asymmetric creation of chiral centers with chiral hydroboration agents, makes the reaction most valuable for asymmetric organic synthesis. In some of the cases, however, this has been achieved by diborane itself as shown in the synthesis of monensin by Kishi et al. A stereospecific synthesis of its seven carbon. component has been accomplished by two hydroboration reactions (Eq. 129) 209. ... 

An interesting feature that made the commercialization of the synthesis of linear carbonates possible is that both linear and cyclic carbonates easily undergo transesterification with alcohols (Scheme 6.9). This process is used industrially for the synthesis of diphenylcarbonate from DMC.72 The coproduct methanol is recycled to DMC. Nevertheless, once a highly efficient direct C02 process for an organic carbonate is found, transesterification makes possible the production of any other carbonates. 

Webster, D. C., and Crain, A. L. Synthesis and Applications of Cyclic Carbonate Functional Polymers in Thermosetting Coatings, Progress in Organic Coatings (2000) 275-282. 

Oxalyl Chloride as a Cl Synthon. Although oxalyl chloride is mainly employed as a C2 equivalent in organic synthesis, there are successful examples of using this reagent for the introduction of a single carbon functionality. Thus, in addition to the expected formation of l,4-dioxane-2,3-diones when reacted with 1,2-diols, the reaction can also lead to the preparation of cyclic carbonates.Also, oxalyl chloride can react with ambident dianions as a Cl synthon (eq 27). ... 

A-Heterocyclic carbenes (NHCs), used as organocatalysts, have received great interest due to their unique reactivity and selectivity observed in many different types of organic reactions (for selected recent reviews see [250-261]. More recently, NHC-mediated reactions have also been employed for polymer synthesis ([262-264] for selected reviews see [20, 265-267]), especially in the ROP of heterocyclic monomers, such as lactides [268-272], lactones [273-276], epoxides [277-279], cyclic carbonates [280], cyclic siloxanes [281, 282], and A-carboxyl-anhydrides [283, 284]. NHC-mediated step-growth polymerization has also been reported [285-287]. 

A siUca-SIL [BMIM]BF4 material was synthesized [80]. The catalyst proved to be an efHdent heterogeneous catalyst for solventless synthesis of cyclic carbonates from epoxides and CO2 under supercritical conditions, which required no additional organic solvents either for the reaction or for the separation of product. High yields with excellent selectivity were obtained. Moreover, the catalyst could be easily... 

Metal-salen complexes immobilized on amorphous or mesostructured SiO were also investigated as acid-base catalysts for the cycHc carbonates synthesis imder continuous operation in gas phase. Despite the high selectivity to the cyclic carbonates the major drawback of these organic-inorganic hybrid catalysts were the catalyst deactivation, likely due to the cleavage of bonds which link the salen ligand and SiO imder the reaction conditions [78,82,106-108,111-113]. 

Sakai T, Tsutsumi Y, Ema T (2008) Highly active and robust organic-inorganic hybrid catalyst for the synthesis of cyclic carbonates from carbon dioxide and epoxides. 

Electrochemical synthesis of cyclic carbonates from CO2 with epoxides, anilines, alcohols, and glycols was reported [53-60]. For example, Dunach et al. [54] conducted the reaction of epoxides with CO2 to the corresponding cyclic carbonates by an electrochemical method in the presence of nickel(II) complexes. In these methods, harmful organic solvents, supporting... 

The above mentioned direct synthesis of DMC requires organic or inorganic dehydration reagents to get high DMC yields because of the reaction equilibrium. On the other hand, the transesterification of cyclic carbonate with methanol relatively easily gives high DMC yields. ILs can also be used as the catalysts for this reaction. Scheme 26 illustrates the generally accepted reaction mechanism for the base catalyzed transesterification of... 

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