Cyclic carbonate elimination

Figure 9. Structure of the cyclic carbonate elimination product (9) isolated from the BTFE cationic polymerization of SOCM. Symmetrical bis(chloromethyl) spiro model monomer (10) used in comparative cationic polymerizations.

Hydroxy-( , )-a,y-dienylsulfones are prepared by an analogous one-pot dehydration procedure via an elimination reaction of the corresponding cyclic carbonate [21]... 

Takata and Endo, 1988]. A cyclic carbonate and cyclic ether are eliminated as by-products in reaction pathways a and b, respectively. Polymer LXXIV contains both ether and carbonate functional groups in the polymer chain. 

All-carbon ene reactions can go in reverse when ring-strain is released 6.24. This reaction is curious, because it could also be considered as a homologue of a [1,53-sigmatropic rearrangement—it is quite common to think of the chemistry of cyclopropanes as similar to that of alkenes. With heteroatoms in the chain it is possible to drive such reactions in reverse without having to release strain. Thus esters such as acetates and benzoates undergo a cyclic (3-elimination on pyrolysis. This type of elimination is known to be syn... 

Metathesis of alkenes has been reviewed in terms of cross-metathesis, ring opening and closing, disproportionation, transmutation, and self-metathesis.34 A review on catalytic processes involving ft -carbon elimination has summarized recent progress on palladium-catalysed C-C bond cleavage in various cyclic and acyclic systems.35... 

It has been found that decarboxylation may be completely eliminated if cationic polymerization of cyclic carbonates is initiated with alkyl iodide or bromide. It is believed that polymerization proceeds with the participation of covalent active species favoring propagation over side reactions leading to C02 elimination [204]. It is interesting to note, that BF3-initiated polymerization of some cyclic carbonates leads to high molecular weight polymers (M > 10s) [205]. 

The aromatization of streptamine by pyrolysis supported the evidence for the cyclic carbon skeleton, although it is to be noted that structural conclusions drawn from pyrolytic data are ordinarily open to question. Since the aromatization was achieved without elimination of nitrogen, the degradation also yielded information regarding the orientation of the nitrogen atoms. It was found that when hexaacetylstreptamine was heated in a sealed tube at 350 for one hour, 3.5 moles of acetic acid were produced and two crystalline products were obtained. One of the products was shown to be identical with 2,4-diacetamidophenol (X). ... 

Macro ides - Clinical trials are underway for erythromycin A, 11,12-cyclic carbonate,72 which is said to be more active than erythromycin A. Josa-mycin was tolerated better than erythromycin in fasting patients, while plasma concentrations, half lives, and elimination constants were equivalent.73 Josamycin was less active than rosamicin or erythromycin A against aerobic cocci while clindamycin was more active than all three against anaerobes.714,75... 

For examples of P-carbon elimination in late transition metal systems, Bergman et al. identified P-methyl transfer with four-membered ruthenacycles, which is driven by the formation of Ji-allyl and Ji-oxallyl complexes. Warming the solution of oxaruthenacycle 58 to 45°C led to formation of methane and cyclic enolate complex 60 [76]. ji-Oxallyl complex 59 initially arises from P-methyl... 

Organic dihalides, aliphatic or aromatic, with >4 carbon atoms between the two halogens do not present any difficulties other than those encountered with their monohalo analogues. To prevent coupling, which in this case may be favored by intramolecular ring closure, the addition of the dihalide should be slow Et20 is used but THE is preferable . With several cyclic dihalides, elimination or fragmentation occurs, e.g. ° ... 

Abstract Palladium-catalyzed C-C bond cleavage via p-carbon elimination occurs in various cyclic and acyclic systems. Thus, the reaction can be utilized as one of fundamental and effective tools in organic synthesis. The recent progress in this field is summarized herein. 

The ring-opening polymerization of the cyclic carbonate methyl 4,6-0-benzylidene-2,3-6>-carbonyl-a-D-glucopyranoside has recently been described. This polymerizes at relatively low temperatures (60°C), without any elimination of carbon dioxide, to give polycarbonates in good yields and medium molecular weights [137]. 

Haba O., Tomizuka H., Endo T, Anionic ring-opening polymerization of methyl 4,6-0-benzylidene-2,3-0-carbonyl-a-D-glucopyranoside A first example of anionic ring-opening polymerisation of five-membered cyclic carbonate without elimination of CO2, Macromolecules, 38, 2005, 3562-3563. 

They demonstrated the reversible CO capture-release ability of MCM-41-NHC and speculated the mechanism shown in Figure 8.24. First a MCM-4I-NHC-CO2 adduct is formed by reaction with CO that subsequently is attacked by the epoxide to generate a new zwitterion. Then a nucleophilic attacks of the formed oxy anions toward the carbon atom of carbonyl group produced cyclic carbonates by intramolecular cyclic elimination. Moreover,... 

Ariga, T., Takata, T., Endo, T., 1997. Cationic ring-opening polymerization of cyclic carbonates with alkyl halides to yield polycarbonate without the ether unit by suppression of elimination of carbon dioxide 1. Macromolecules 30, 737—744. 

Kang and co-workers have reported reactions of open-chain vinyl-substituted cyclic carbonates with many stabilized and nonstabilized carbon nucleophiles,heteroatom nucleophiles, hydride equivalent,and vinyl and aryltin reagents. Retention of configuration has been observed for malonate, for thiophenolate, and for the conjugate base of phthalimide. In the absence of nucleophile a proton elimination ensues (Scheme 44). The reaction with iodobenzene produces a reductive ring opening by a variant of the Heck reaction. ... 

Conversion of cyclic carbonates into unsaturated aldehydes (Scheme 45) requires acetic acid as solvent to protonate the intermediate alkoxide. The more acidic protons for elimination from the intermediate are now those in the —CH2OH group. ... 

Polycarbonates have attracted attention in recent years because of their potential use in biomedical applications based on their biodegradability, biocompatibility, low toxicity and good mechanical properties [67]. These polymers can be prepared by the ROP of cyclic carbonate monomers by anionic, cationic, and coordination catalysts. However, lipase-catalyzed polymerization seems to be a feasible alternative to prepare polycarbonates as chemical methods often suffer from partial elimination of carbon dioxide (resulting in ether linkages), require extremely pure monomers and anhydrous conditions. 

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