Lactones ketones

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

CH2N2 did not react with esters, y-lactones, ketones or alcohols. 

Carbonyl oxides are extremely photolabile even under matrix conditions and irradiation with red light (600 nm) rapidly produces dioxrranes (82). The dioxi-ranes are stable under these conditions but at 400-nm irradiation are converted into esters (83) or lactones. Ketones have been observed as byproducts in the carbene-O2 reactions in frozen matrices. Since the reaction of triplet carbene with O2 is very... 

Cellobiose Octaacetate and Glucose Pentaacetate. The results on both compounds were similar. Samples irradiated at 253.7 and 313 mfi, both in the presence of oxygen and in vacuum, were saponified. Infrared analysis of the saponified residues showed that all samples had carbonyl absorption at 5.76 to 5.78 microns, owing to lactones, ketones,... 

The most widely used method for quantifying FFAs is gas chromatography (GC), which has attained widespread favor due to its versatility, high sensitivity and relatively low cost. GC complexed with a flame ionization detector is used routinely to quantify FFAs, either directly or derivatized as fatty acid methyl esters (FAME). GC with mass spectroscopic detection has become the favored technique for quantification of volatile compounds derived from lipids (esters, lactones, ketones, alcohols and acids). 

Micro-organisms also have a potential to form fruity components like alcohols, esters, lactones, ketones and terpenes. These substances are, however, also obtainable by chemical syntheses as well as by relatively simple extraction from the natural fruit. Additionally, fermented fruit flavours in many cases are not very typical for a certain fruit species and therefore may be used only as raw materials for compounded flavours. Presumably this is the reason why the corresponding processes have not yet been transferred onto an industrial scale. This is not true for the fermentative generation of well defined single substances which may serve as natural flavour raw materials for compounded flavours (cf. chapter 3.2.1.1.2). 

Esters, lactones, ketones, and nitriles with secondary a-carbons can all be a-hydrox-ylated using the peroxide Mo05/Pyridine/HMPA [44-46]. This method does not in olve hydroperoxide intermediates so that elimination to the ketone does not occur. 

Cyclopropane rings. Synthesis of (diene)Fe(CO)3 complexes, and of cyclohexenones, lactones, ketones, or sulfones, can follow from the opening of vinylcyclopropanes with Fe(CO)s under either thermal or photochemical conditions. Reactions of the vinylcyclopropane (15) with Fe(CO>5 under thermal conditions resulted in ring opening with concomitant hydrogen shift to form the diene complex (16) (eq 7) 2.63,64... 

Recently, nickel-catalyzed cross-couplings of organosUicon reagents with unactivated secondary alkyl bromides have been disclosed. Functional groups such as fluoride, chloride, ether, lactones, ketones, acetals, and cyanides are stable under the reaction conditions. Bathophenanthroline appears to be the best ligand for these transformations [96]. 

When the compound for identification fails to respond to test 4 (aldehyde or ketone), the next class reactions to apply are the hydroxatnic acid teat and saponification, i.e., hydrolysis in alkaline solution. These are the class reactions for esters and anhydrides the rarely-encountered lactones react similarly. 

Baeyer-Villiger Oxidation- oxidation of ketones to esters and lactones via oxygen insertion... 

Analysis Another lactone FGl reveals the true TM (A). Our normal discormection a of an a,p-unsaturated carbonyl compound gives us the 1,5-dicarbonyl compound (B) and the ketone (C) clearly derived from phenol. Alternatively we could disconnect bond b to the keto-ester (D) with the further discormection shown ... 

The reductive coupling of aldehydes or ketones with 01, -unsaturated carboxylic esters by > 2 mol samarium(II) iodide (J.A. Soderquist, 1991) provides a convenient route to y-lactones (K. Otsubo, 1986). Intramolecular coupling of this type may produce trans-2-hy-droxycycloalkaneacetic esters with high stereoselectivity, if the educt is an ( )-isomer (E.J. Enholm, 1989 A, B). 

The 1,6-difunctional hydroxyketone given below contains an octyl chain at the keto group and two chiral centers at C-2 and C-3 (G. Magnusson, 1977). In the first step of the antithesis of this molecule it is best to disconnect the octyl chain and to transform the chiral residue into a cyclic synthon simultaneously. Since we know that ketones can be produced from add derivatives by alkylation (see p. 45ff,), an obvious precursor would be a seven-membered lactone ring, which is opened in synthesis by octyl anion at low temperature. The lactone in turn can be transformed into cis-2,3-dimethyicyclohexanone, which is available by FGI from (2,3-cis)-2,3-dimethylcyclohexanol. The latter can be separated from the commercial ds-trans mixture, e.g. by distillation or chromatography. 

The furo- and pyranobenzopyranones 114 and 115 are prepared by the reaction of 0-enolate of i(-keto lactone 113[132], The isoxazolc 117 is obtained by the oxidation of the oxime 116 of a, /3- or, d, 7-unsaturated ketones with PdCh and Na2C03 in dichloromethane[l 33], but the pyridine 118 is formed with PdCl2(Ph3P)2 and sodium phenoxide[134]. 

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]... 

The slow oxidation of primary alcohols, particularly MeOH, is utilized for the oxidation of allylic or secondary alcohols with allyl methyl carbonate without forming carbonates of the alcohols to be oxidized. Allyl methyl carbonate (564) forms 7r-allylpalladium methoxide, then exchange of the methoxide with a secondary or allylic alcohol 563 present in the reaction medium takes place to form the 7r-allylpalladium alkoxide 565, which undergoes elimination of j3-hydrogen to give the ketone or aldehyde 566. The lactol 567 was oxidized selectively with diallyl carbonate to the lactone 568 without attacking the secondary alcohol in the synthesis of echinosporin[360]. 

---