Ethers, carbonates, lactone

Methoxyphenyl tellurium compounds with cyclic ether or lactone functionalities in the imposition to the carbon atom linked to tellurium were detellurated by tributyltin hydride in oxygen-free toluene with elimination of the aryltelluro group2. 

Cleavage of lactones and carbonates. Lactones and carbonates react with bromotrimethylsilane to afford bromocarboxylic acid derivatives (equation I) and bromohydrin trimethylsilyl ethers (equation II), respectively acyclic, aliphatic esters do not react with bromotrimethylsilane. lodotrimethylsilane reacts in an analogous fashion with lactones, but in reaction with ethylene carbonate the main product is 1,2-diiodoethane (equation III). The >-bromocarboxylate derivatives are converted into acid chlorides by reaction with SOCL (equation I). 

Activated carbon, in keeping with the enhanced complexity of carbon-based chemistry, possesses an extensive array of surface moieties, including hydroxyl groups, carboxylic acid groups, aldehyde groups, keto groups, cyclic ethers, and lactone groups. 

In addition to step and chain polymerizations, another mode of polymerization is of importance. This is the ring-opening polymerization of cyclic monomers such as cyclic ethers, esters (lactones), amides (lactams), and siloxanes. Examples of commercially important types are given in Table 10.1. Of those listed, only the polyalkenes are composed solely of carbon chains. Those that have enjoyed the longest history of commercial exploitation are polyethers prepared from three-membered ring cyclic ethers (epoxides), polyamides from cyclic amides (lactams), and polysiloxanes from cyclic siloxanes. 

Among a host of other phosphine-catalysed reactions in which the initial step is the formation of a reactive phosphoniobetaine intermediate by addition to a carbon-carbon double or triple bond are intramolecular cyclisations leading to benzobicyclo[4,3,0]-compounds, " cyclic ethers " and lactones,and a great many intermolecular reactions, e.g., a [3 -b 3]-annulation of modified t-butyl allylic carbonates and alkylidenemalonitriles to give cyclohexenes,phosphine- (and fluoride)- catalysed routes to 1,4-benzothiazepines from cyclic sulfenamides and alkynes, a [4- -3]-annu-lation of allylic carbonates with methyl coumalate to give functionalised bicyclo[3.2.2]nonadienes, the a-carbon addition of cyanide ion, generated in situ from cyanohydrins, to activated alkynes, and a stereoselective... 

Photolytic. Thin films of endosulfan on glass and irradiated by UV light (A, >300 nm) produced endosulfandiol with minor amounts of endosulfan ether, a lactone, an a-hydrox-yether and other unidentified compounds (Archer et al., 1972). When an aqueous solution containing endosulfan was photooxidized by UV light at 90-95°C, 25, 50 and 75% degraded to carbon dioxide after 5.0, 9.5 and 31.0 hours, respectively (Knoevenagel and Himmelreich, 1976). 

The fluorination of cyclic ethers, esters, lactones, and cyclic and acyclic carbonates can be achieved by anodic oxidation of a large amount of the liquid substrates and a small amormt of Et4NF-4HF (only 1.5—1.7 equiv. of F to the ether) at a high current density (150 mA cm ) (Schemes 17 and 18) [27]. 

Lactones loss of a-suhstituents (attached to ether carbon), decatbonylation, for aromatic lactones also double decarbonylation... 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

Telomerization Reactions. Butadiene can react readily with a number of chain-transfer agents to undergo telomerization reactions. The more often studied reagents are carbon dioxide (167—178), water (179—181), ammonia (182), alcohols (183—185), amines (186), acetic acid (187), water and CO2 (188), ammonia and CO2 (189), epoxide and CO2 (190), mercaptans (191), and other systems (171). These reactions have been widely studied and used in making unsaturated lactones, alcohols, amines, ethers, esters, and many other compounds. 

For substituted lactones this method gave a low yield of the spiroketal 189 (<5%). For 5,6-dimethylvalerolactone a second scheme has been suggested involving treatment of ketoalcohol 190 with potassium carbonate in methanol to form enole ether acetal 191 in quantitative yield (90JOC5894). 

As inert as the C-25 lactone carbonyl has been during the course of this synthesis, it can serve the role of electrophile in a reaction with a nucleophile. For example, addition of benzyloxymethyl-lithium29 to a cold (-78 °C) solution of 41 in THF, followed by treatment of the intermediate hemiketal with methyl orthoformate under acidic conditions, provides intermediate 42 in 80% overall yield. Reduction of the carbon-bromine bond in 42 with concomitant -elimination of the C-9 ether oxygen is achieved with Zn-Cu couple and sodium iodide at 60 °C in DMF. Under these reaction conditions, it is conceivable that the bromine substituent in 42 is replaced by iodine, after which event reductive elimination occurs. Silylation of the newly formed tertiary hydroxyl group at C-12 with triethylsilyl perchlorate, followed by oxidative cleavage of the olefin with ozone, results in the formation of key intermediate 3 in 85 % yield from 42. 

Silyl enol ethers and ketene acetals derived from ketones, aldehydes, esters and lactones are converted into the corresponding o/i-unsaturated derivatives on treatment with allyl carbonates in high yields in the catalytic presence of the palladium-bis(diphenylphosphino)ethane complex (32). A phosphinc-free catalyst gives higher selectivity in certain cases, such as those involving ketene acetals. Nitrile solvents, such as acetonitrile, are essential for success. 

The reaction of a, to-diols or cyclic ethers with a stoichiometric amount of BTMA Br3 in carbon tetrachloride, or in acetic acid in the presence of aqueous Na2HP04 or CH3COONa, at 60-70°C gave lactones. The results are shown in Figure 22. 

The final ring coupling reaction is usually an O-alkylation of the sodium enolate with a methyl sulfonate-, bromo-, or chloro-butenolide in acetonitrile or an ether solvent (8.22-24). Use of the methyl sulfonate derivative is least preferred because of its poor stability (9,24). The isolated hydroxymethylene lactone can be allowed to react with the bromobutenolide using potassium carbonate in hexamethylphosphoric triamide (caution a potential carcinogen). 

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