From Esters and Lactones

The photoelimination of carbon dioxide from esters and lactones is a process that has been the subject of detailed investigations. Discussion here is limited to nitrogen containing systems. 3,4-Diphenylsydnone (464), on irradiation in benzene, is converted via the nitrile imine 465 into 2,4,5-triphenyl-1,2,3-triazole (466)388 initial bond formation between N-2 and C-4 followed by loss of carbon dioxide to give the diazirine 467 is proposed to account for the formation of the nitrile imine. Nitrile imines generated in this way have been trapped with alkenes and alkynes to give pyrazoles389... 

Difluoroenol ethers are also available from esters and lactones by a Wittig-like reaction with CF2Br2/P(NMe2)3 in the presence of a reducing agent [38, 39] (Scheme 2.202). 

Scheme 2.202 Synthesis of difluoroenol ethers from esters and lactones [38, 39].

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]... 

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 most widely used reagent for partial reduction of esters and lactones at the present time is diisobutylaluminum hydride (DiBAlH).83 By use of a controlled amount of the reagent at low temperature, partial reduction can be reliably achieved. The selectivity results from the relative stability of the hemiacetal intermediate that is formed. The aldehyde is not liberated until the hydrolytic workup and is therefore not... 

E. Tertiary alcohols from ketones, esters, and lactones... 

In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly different infrared absorptions. The spectra of acid fluorides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bonding induced shifts in the spectra. Preliminary results from the use of these reactions to characterize y-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. 

Dihexylxylaramide (2). To a 250 mL round-bottom flask equipped with a magnetic stirrer was added methanol (150 mL), and the flask then cooled to 5 C. Acetyl chloride (5 mL) was added to the cold methanol and then xylaric acid (18 g, 0.18 mol, reference 18) was added to the methanolic HCl solution. The reaction mixture was refluxed for 16 h, concentrated to a syrup, and residual water removed from the syrup by azeotropic distillation with benzene. Esterification was complete but the product (1) contained more than one ester component as both ester and 5-membered lactone functions were observed in its IR spectrum (neat, 1745 and 1795 cm, ester and lactone C=0 respectively). 

Zinc enolates obviously give a better induction than the corresponding lithium enolates. This condensation also occurs with good yields with various enolates generated from ketones, esters and lactones, however, the enantiomeric excesses are poor27. 

Natural products are obtained directly from plant or animal sources by physical procedures. Nature-identical compounds are produced synthetically, but are chemically identical to their natural counterparts. Artificial flavor substances are compounds that have not yet been identified in plant or animal products for human consumption. Alcohols, aldehydes, ketones, esters, and lactones are classes of compounds that are represented most frequently in natural and artificial fragrances. 

The biotechnological production of flavour compounds is particularly focused on esters and lactones. Lipase from Mucor miehei is the most widely studied fungal lipase [30-35]. Esters of acids from acetic acid to hexanoic acid and alcohols from methanol to hexanol, geraniol and citronellol have been synthesised using lipases from Mucor miehei, Aspergillus sp., Candida rugosa, Rhizopus arrhizus and Trichosporum fermentans [32-37]. 

The at complex from DIB AH and butyllithium is a selective reducing agent.16 It is used tor the 1,2-reduction of acyclic and cyclic enones. Esters and lactones are reduced at room temperature to alcohols, and at -78 C to alcohols and aldehydes. Acid chlorides are rapidly reduced with excess reagent at -78 C to alcohols, but a mixture of alcohols, aldehydes, and acid chlorides results from use of an equimolar amount of reagent at -78 C. Acid anhydrides are reduced at -78 C to alcohols and carboxylic acids. Carboxylic acids and both primary and secondary amides are inert at room temperature, whereas tertiary amides (as in the present case) are reduced between 0 C and room temperature to aldehydes. The at complex rapidly reduces primary alkyl, benzylic, and allylic bromides, while tertiary alkyl and aryl halides are inert. Epoxides are reduced exclusively to the more highly substituted alcohols. Disulfides lead to thiols, but both sulfoxides and sulfones are inert. Moreover, this at complex from DIBAH and butyllithium is able to reduce ketones selectively in the presence of esters. 

Table 2 also shows surface concentration of quinones and esters or lactones, often referred to as "neutral oxygen compounds" in the rubber literature actually these are basic oxygens, but not basic in an aqueous environment. The quinone content is estimated from the amount of carbon monoxide evolved in pyrolysis minus the weak acid content (presumed to be phenolic acids,not neutralized at pH 8.2), and the ester and lactone content is estimated from the carbon dioxide evolved in pyrolysis minus the strong acid content (presumed to be carboxylic acids neutralized at pH 8.2). 

A new and efficient method for the synthesis of optically active esters and lactones having a tertiary or a quaternary stereogenic centre at the y -position has been developed.28 Treatment of optically active 1-chlorovinyl p-tolyl sulfoxides having two different substituents at the 2-position with the lithium enolate of t -butyl acetate gave optically active adducts in 99% chiral induction from the sulfur stereogenic centre. 

The flavor constituents of plain and roasted cashew nuts have not been previously reported in the literature. In the present study, aroma compounds have been isolated from plain, oven-roasted and oil-roasted cashew nuts by simultaneous distillation extraction and by steam distillation followed by selective extraction, after pH adjustment. Compound identification was carried out by GC and GC-MS analyses. Esters and lactones are present in plain cashews whereas roasted samples also contain pyrazines. 

To sum up, the flavor constituents of plain and roasted cashew nuts are reported here for the first time. The mild flavor of cashew nuts can be attributed to the carbonyls, esters and lactones, especially to 5-heptene-2-one and 1,3-propanediol diacetate. Upon roasting, 2,6-dimethyl pyrazine, 2,6-diethyl pyrazine and the furanone are formed in larger amounts and from flavor profile also these compounds are likely to play a significant role in the characteristic aroma of roasted cashew nuts. 

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