Oxirane/cyclic carbonate

Treatment of cyclic carbonates of 1,2-diols with thiocyanate ion at temperatures of 100 °C or higher yields thiiranes (Scheme 145) (66CRV297, 75RCR138). Thiourea cannot replace thiocyanate satisfactorily, and yields decrease as the carbonate becomes more sterically hindered. The reaction mechanism is similar to the reaction of oxiranes with thiocyanate (Scheme 139). As Scheme 145 shows, chiral thiiranes can be derived from chiral 1,2-diols (77T999, 75MI50600). 

Cyclic carbonates have been prepared in the regiospecific ring-opening of oxiranes by butyrolactones catalysed by the quaternary ammonium salt (Scheme 3.6)... 

Yields are variable, but the reaction appears to be promoted by the presence of alkoxymethyl substituents on the oxirane ring. Reactions with p-propiolactones give lower yields (<10%). Cyclic carbonates can also be obtained from the zinc(II) promoted reaction of oxiranes with carbon dioxide [62] the stereochemistry of substituents on the oxirane are retained in the carbonate. 

Naito et al.si have reported that the addition of oxirane derivatives to C02 is catalyzed by potassium carboxylates or carbonates in the presence of a crown ether cyclic carbonates (42) constitute the main product. 

Oxacyclic monomers constitute the most widely investigated class of heterocyclic monomers regarding both academic and industrial interest. In particular, the coordination polymerisation of cyclic ethers such as epoxides (oxiranes) and of cyclic esters such as lactones, lactides and cyclic carbonates has been considered. 

Since oxiranes are representative heterocyclic monomers containing an endo-cyclic heteroatom, and the most commonly polymerised of such monomers, they have been subjected to copolymerisations with heterocyclic monomers containing both an endocyclic and an exocyclic heteroatom. Coordination copolymerisations of heterocyclic monomers with different functions are focused on oxirane copolymerisation with cyclic dicarboxylic acid anhydride and cyclic carbonate. However, the statistical copolymerisation of heterocyclic monomers with an endocyclic heteroatom and monomers with both endocyclic and exocyclic heteroatoms have only a limited importance. Also, the block copolymerisation of oxirane with lactone or cyclic dicarboxylic acid anhydride is of interest both from the synthetic and from the mechanistic point of view. Block copolymerisation deserves special interest in terms of the exceptionally wide potential utility of block copolymers obtained from comonomers with various functions. It should be noted, however, that the variety of comonomers that might be subjected to a random, alternating and block polymerisation involving a nucleophilic attack on the coordinating monomer is rather small. 

It seems that the initiation step of the copolymerisation most likely involves the oxirane reaction [according to scheme (3)]. Zinc alcoholate species formed in this reaction can easily propagate the copolymer chain, coordinating and enchaining both the oxirane [scheme (3)] and the cyclic carbonate [scheme (15)] comonomers. However, in the case of the cyclic carbonate, its enchainment may also proceed according to scheme (14), leading to decarboxylation. Thus, the obtained poly(ether-carbonate)s are characterised by a lower content of carbonate units with respect to the ether units [82,146]. 

Copolymerisation of propylene oxide as well as other oxiranes with carbon dioxide in the presence of zinc-based coordination catalysts is generally accompanied with the formation of a cyclic five-membered carbonate, propylene carbonate or another alkylene carbonate [147,206,207,210,212,230]. The alky-lene carbonate, however, is not the precursor for poly(alkylene carbonate), since it hardly undergoes a polymerisation under the given conditions [142-146],... 

The standard preparation of 2-oxazolidinones is by treatment of /3-amino alcohols with phosgene or its synthetic equivalents ethyl chloroformate, dialkyl carbonates or even urea (equation 174). Isocyanates react with oxiranes in the presence of amines to yield 2-oxazolidinones (equation 175) (79LA200). The action of isocyanates on cyclic carbonates results in 2-oxazolidinones (equation 176) and photolysis of alkyl azidoformates affords oxazolidinones via intermediate nitrenes (equation 177). 

Triphenylantimony difluoride (Ph3SbF2) catalyzes the formation of cyclic carbonates from oxiranes and C02 (Equation (33)).65 The best result is obtained when the reaction is conducted using a high pressure of C02 at 180 °C in HMPA. Under similar reaction conditions, Ph3BiF2 shows only a low catalytic activity. 

The transformation of oxiranes into other oxygen-containing heterocyclic systems (e.g., cyclic ethers, dioxolanes, orthoesters, lactones, and cyclic carbonates), via a variety of heterolytic, homolytic, enzymatic, and single-electron transfer processes, has been reviewed <2004RJ01227>. 

Although the C(17)-oxiran (327) failed to react with most nitrogenous bases (NH3, NH2, phthalimide ion, urea, etc.), guanidine effected substitution at C(20), which was followed by expulsion of ammonia to give the oxazoline (328). This compound could not be hydrolysed, but was deaminated by nitrous acid to give the 17/S,20-cyclic carbonate (329). 

The synthesis of 5-membered cyclic carbonates is carried out by the reaction of oxirane with carbon dioxide in the presence of various quartemary ammonium salts catalyst as shown in Scheme 1 and their results are listed in Table 1. 

Two groups have independently explored dipolar cycloadditions of oxiranes with chlorosulfonyl isocyanate. Treatment of oxiranes with C1S02N=C=0 in benzene <84JHC1721, 84SC687) or in CH2C12 <86SC123> gives rise to either cyclic carbonates or 2-oxazolidones, or both after hydrolytic workup (Equation (27)). 

Vinyl oxiranes form cyclic carbonates in a regio- and stereoselective fashion when treated with C02 in the presence of a Pd(0) complex <85JA6123>, see also <85CL199>. 

Five-membered cyclic carbonates are easily available as a result of the insertion of gaseous carbon dioxide into an oxirane ring (see review [12.]). Recent work in the field of new methods for preparing cyclic carbonates is dedicated primarily to the development of new catalytic systems and the synthesis of monofunctional compounds from epoxides and carbon dioxide (see, for example, reviews [13-16]). Monocyclic carbonates are used in a wide spectrum of applications solvents, components of liquid electrolytes, reactive diluents, chemical intermediates, and so on. It should be noted that this preparation also solves the problem of chemical fixation and utilization of C02. 

Polycarbonates and cyclic carbonates are obtained by the well-known and well-studied reactions of CO2 and oxiranes (Scheme 7). These reactions have also been successfully performed in supercritical mixtures. [28] It turned out, however, that the industrial production of ethylene carbonate (similar to propylene carbonate) in a liquid (product) phase (190-200 °C, total pressure 80 bar) is more economical for capacities of 4000 t per year and installation when it is run nearly stoichio-metrically. [44] In the cases of substituted or polycyclic oxiranes, solvents are usually added and 1 to 40 bar of CO2 are introduced, depending on the catalyst employed. [28] However, the development of a CO2-soluble Zn catalyst formed the polycarbonate from... 

Transformation of carbon dioxide, particularly, in synthesis of oxazolidi-nones and cyclic carbonates or copolymerization with oxiranes 07CRV2365. 

Rokicki, G., Kuran, W., Pogorzelska-Marciniak, B., 1984. Cyclic carbonates from carbon dioxide and oxiranes. Monatshefte fiir Chemie 115, 205—214. 

The interest in the elaboration of oxirans to cyclic carbonates is exemplified by three papers which have appeared this year. The conversion of (106) -> (107) is well known using elevated temperatures and pressures. Various catalysts have been employed and the range has been extended to include pentavalent organo-antimony compounds. " Good yields under much milder conditions have been achieved using a metal halide and a Lewis-base catalyst. The cyclic carbonate... 

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