Keto-carbonyl groups

The keto carbonyl group can be hydrogenated fairly readily and many of the characteristics of aldehyde hydrogenations also apply here. Initially, the alcohol is produced, but overhydrogenation may result in hydrogenolysis of the C-O bond to form the alkane (Fig. 2.23). Acidic media facilitate hydrogenolysis whereas basic media or basic substituents inhibit hydrogenolysis. 

During the degradation the keto-carbonyl groups increased in amount as obtained by attenuated total reflectance (ATR)-FTIR. In the basic environment a growing peak corresponding to carboxylate anion is observed (13). 

The biosynthesis of terpenes clearly follows a somewhat different course from fatty acids in that branched-chain compounds are formed. One way that this can come about is for 2-oxobutanoyl coenzyme A to undergo an aldol addition at the keto carbonyl group with the ethanoyl coenzyme A to give the 3-methyl-3-hydroxypentanedioic acid derivative, 8 ... 

But it is interesting to note that the 50/50 EVA/LDPE blend processed under the same conditions shows a single well-resolved >C=0 stretching band at 1740 cm1 (Figure 5.4) which indicates that there is no trace of keto carbonyl groups. 

In this section it will be shown, how special molecular constitution and conformation may force the formation of macrocycles. Furthermore, examples will be discussed in which the photoinduced electron transfer (PET) from electron rich functional groups to the excited keto carbonyl group initiates a macrocyclization. The exceptionally successful PET assisted macrocyclizations of phthalimides will be treated separately in Sec. 3.4.6. 

An ester carbonyl group is known to be generally less reactive than an aldehyde or a ketone carbonyl group. As a result, cycloaddition reactions of esters under thermal conditions are very rare. In a unique case, Chatani et al. [23] found that an ester functionality also participates in the carbonylative cycloaddition reaction of a-ketolactones (Eq. 11). The presence of a bulky group next to the keto carbonyl group is required for this selective reaction. 

There is another reason for the poor ee in the hydrogenation of 8. The steric difference between the two groups on both sides of the keto carbonyl group is minor. Hence, efficient enantioselection by the Pt-CD system requires considerable steric differences between the two alkyl (and aryl) groups on both sides of the carbonyl group. This is illustrated by some examples in Scheme 2. 

Treatment of particular fully conjugated heterocyclic enaminediones with NaBH4 resulted in a chemoselective reduction of the keto carbonyl group, followed by a stereoselective reduction of the carbon-carbon double bond135 (Scheme 100). Catalytic hydrogenation allowed a complete reduction of the second carbonyl group. 

The difference spectra of the different charge separated states are dominated by the absorption changes of the chromophores and the quinones (Buchanan et al., 1992). Band shifts from 1743 cm to 1755 cm and from 1672 cm to 1712 cm are characteristic of the oxidation of bacteriochlorophyll b in an aprotic environment. They correspond to the absorbance changes of the 10-c-ester- and 9-keto-carbonyl groups of the primary... 

The high-resolution molecular mass of the compound gives the molecular formula which corresponds to eight double bond equivalents. The H broadband decoupled NMR spectrum shows a keto carbonyl group (185.2), two carboxy functions (176.4 and 170.4) and four further signals in the sp chemical shift range (146.8,... 

A nitrene (derived from a nitro group and triethyl phosphite) reacts with an adjacent ethoxycarbonylvinyl group to form a quinoline in moderate yield. Replacing the ester by a keto carbonyl group results in much lower yields. 

Whenever two or more readily interconvertible isomers of a substance are in (dynamic) equilibrium, there will generally be migration of double bonds. The most often encountered tautomerism is between the keto and tire enol forms of an oxygen-containing compound. Ethyl acetoacetate is probably one of the earliest known cases of keto-enol tautomerism. While the keto-form, XXH, shows a low intensity (e 20) band around 275 mp characteristic of an isolated keto-carbonyl group, the enol form, XXIII, shows a high intensity band (< 18,000) around 245 mp due to the conjugated double... 

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