Ketones from £-keto acids

Typical examples are listed in Table 2.1. A few oxidations are effected by RuO but in general it is too powerful an oxidant for this purpose. The system RuCyaq. NaCl-CCy Pt anode oxidised benzyl alcohol to benzaldehyde and benzoic acid and p-anisaldehyde to p-anisic acid [24], and a wide range of primary alcohols and aldehydes were converted to carboxylic acids, secondary alcohols to ketones, l, -diols to lactones and keto acids from RuOj/aq. NaCl pH 4/Na(H3PO )/Pt electrodes (Tables 2.1-2.4). The system [RuO ] "/aq. K3(S303)/Adogen /CH3Cl3 oxidised benzyhc alcohols to aldehydes [30]. The oxidation catalyst TPAP (( Pr N)[RuO ]) (cf. 1.3.4) is extremely useful as an oxidant of primary alcohols to aldehydes and secondary alcohols to ketones without... 

Some noncyclic thioacetals are sometimes used for the preparation of keto acids from aryl halides or keto esters by 1,4-addition on a,p-unsaturated ketones (Scheme 3). 

Reaction with ketones (1, 369-370). Mock and Hartman3 have improved the original procedure for synthesis of /3-keto esters from ketones by using triethyl-oxonium fluoroborate as the Lewis acid catalyst rather than boron trifluoride. Thus cyclohexanone (1) is converted into 2-carboethoxycycloheptanone (2) in 90% yield under the new conditions the yield using BF3 was 38%. The reaction is... 

Diethyl trimethylsilyloxycarbonylmethanephosphonate" and diethyl car-boxymethanephosphonate " are the preferred reagents for the two-carbon homologation of aldehydes and ketones to give a,/8-unsaturated carboxylic acids, while 2,2-difluoro-l-tosylvinyl-lithium is a novel effective reagent for the preparation of a-keto-acids from carbonyl compounds (Scheme 21). a-Methoxy-aliphatic acids have been prepared from aliphatic aldehydes and chloroform using... 

Products detected or isolated from these oxidations include the corresponding a-hydroxy ketone and a-diketone and also adipic acid (from cyclohexanone) in up to 95 % yield. However, IrCI gives a-chloroketone in quantitative yield . Evidently when the rate of oxidation exceeds enolisation attack is on the keto form, probably via a complex, although this is definite only for Ce(IV) perchlorate, to give a radical, e.g. 

Nitroalkenes react with lithium dianions of carboxylic acids or with hthium enolates at -100 °C, and subsequent treatment of the Michael adducts with aqueous acid gives y-keto acids or esters in a one-pot operation, respectively (Eq. 4.52).66 The sequence of Michael addition to nitroalkenes and Nef reaction (Section 6.1) provides a useful tool for organic synthesis. For example, the addition of carbanions derived from sulfones to nitroalkenes followed by the Nef reaction and elimination of the sulfonyl group gives a,P-unsaturated ketones (Eq. 4.53).67... 

In general, esters of /3-keto-acids are formed from two molecules of ester, and /3-diketones from ester and ketone. The use of formic esters leads, in both cases, to hydro xymethylene compounds ... 

Hydrolysis of the new imine then allows formation of a ketone as part of an a-keto acid, and an amine which is the previously mentioned pyridoxamine 5 -phosphate. Since this imine is the product from an amine and a ketone, it is termed a ketimine. These reactions are reversible in nature, allowing amino acids to be converted into keto acids, and keto acids to be converted into amino acids (see Section 15.6). 

Nakata showed that stoich. RuOyCCl oxidised steroidal diols to the corresponding ketones [237] electrogenerated RuO from RuO /aq. NaCl/Na(H3PO ) pH 4/ Pt electrodes converted diols to lactones and keto acids (Tables 2.1-2.4) [267] and RuCyaq. 10(0H)3/CC1 -CH3CN oxidised 3-(benzyloxy)-l,2-octanediol to the acid (Tables 3.4, 3.5) [107]. A diol was converted to a lactone by stoicheio-metric oxidation with RuOyCCl as part of the total synthesis of the quassinoid ( )-amarolide [82],... 

Reaction between a long-chain ketone and a diol will lead to a surfactant that contains a ketal bond. The synthesis is analogous with those given in Figs. 13 and 14 for the preparation of acetal surfactants [52]. Ketal-based surfactants have also been prepared in good yields from esters of keto acids by either of two routes, as shown in Fig. 15 [53-55]. 

The asymmetric transamination from chiral a-amino acids 1021 and amino acid derivatives (57) (esters 86,103), amino alcohols 104 ) to carbonyl functions in prochiral substrates (58) (a-keto acids 102), a-keto esters 86,103), ketones 103b d) was described... 

Acylation of the keto acid (637) leads to the isobenzopyrylium salt (638) (77CHE1183). However, the isobenzopyrylium salt (639), a potential intermediate for the synthesis of analogues of berberine alkaloids, results from the formylation of the substituted ketone or the isochromanone (640) using dichloromethyl butyl ether (Scheme 251) (81CHE221). A second product, the 5-oxoniachrysene (641), is formed and this compound may also be obtained by reaction of the isobenzopyrylium salt with phosphorus pentachloride and then with triethylamine. The intermediacy of a cyclic vinyl ether is proposed. 

This reaction is quite special in that it is an aldol-type addition in which a thioester is the donor (nucleophile) and a keto acid is the acceptor (electrophile). From the discussion in Section 18-8E, you will see that reactions of this kind involving an ester as the donor and an aldehyde or ketone as the acceptor can be achieved in the laboratory only under rather special conditions. For the thioester to function as a nucleophile at the a carbon under the restraints imposed by having the reaction occur at the physiological pH, the catalyzing enzyme almost certainly must promote formation of the enol form of the thioester. The enol then could add to the ketone carbonyl with the assistance of a basic group on the enzyme. This kind of catalysis by enzymes is discussed in Section 25-9C. 

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