Ketones selective

Reduction of carbon-carbon double bond Microalgae easily reduce carbon-carbon double bonds in enone. Usually, the reduction of carbonyl group and carbon-carbon double bond proceeds concomitantly to afford the mixture of corresponding saturated ketone, saturated alcohol, and unsaturated alcohol because a whole cell of microalgae has two types of reductases to reduce carbonyl and olefinic groups. The use of isolated reductase, which reduces carbon-carbon double bond chemoselectively, can produce saturated ketones selectively. 

Results of the cyclohexane oxidation tests are shown in Table 41.4. Mono-oxygenated products are cyclohexanone, cyclohexanol and cyclohexyl hydroperoxide. Cu and Cr were very active, but subsequent tests showed considerable leaching for both metals, whereas Co-Si-TUD-1 did not show ai r leaching. Tests with different Co loadings indicate that the lowest Co concentration has the best conversion and ketone selectivity. Isolated cobalt species are most efficient for the conversion of cyclohexane, as agglomeration of Co reduces... 

The reactants can be prepared by chelation-controlled addition of organometallic reagents to a-(l-ethoxyethoxy)methyl ketones. Selective sulfonylation occurs at the... 

When second generation candidates differing from finasteride only at the C17 position were considered for development, a second team was tasked with defining the synthesis while the first delivery of finasteride was being completed. Three ketones were considered as potential back-up compounds, the s-Bu, i-Pr, and i-Bu ketones (2,19, 3 in Scheme 3.4). Ideally, the new route would allow divergence at a late stage of the synthesis to make both finasteride and the ketone selected for... 

A dienol is also formed via hydrogen abstraction by the excited carbonyl group from a second enone molecule in (4.14). This dienol tautomerizes in C6F6 to give the (3,y-unsaturated ketone selectively, the overall reaction thus being deconjugation of the a,(3-unsaturated ketone415K... 

PICA) show excellent activity and enantioselectivity for reaction of such bulky ketones.Selection of alcoholic solvent is important to achieve high catalytic performance. Thus, hydrogenation of pinacolone with the (5)-TolBINAP/PICA-Ru catalyst (S/C = 100,000) in C2H5OH quantitatively gives (5)-3,3-dimethyl-2-buta-nol in 98% ee (Figure 1.21). The reaction in conventional 2-propanol with the same catalyst results in the S alcohol in only 36% ee. 

Selective reduction of ketones. Selective reduction of a ketone in the presence of an aldehyde is possible by selective reaction of the aldehyde with -bulylamine (4 A molecular sieves), reduction of the ketone with lithium tri-(-butoxyaluminum hydride, and, finally, cleavage ol the aidimine to the aldehyde with aqueous HCI. The three-step sequence can be conducted in one pot. The selectivity is high. The method is not applicable to conjugated ketones because of conjugate reduction. 

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. 

The multi-functionalized ketone A in Scheme 82 is reduced with an excellent ketone-selectivity with (R,R)-39 and a formic acid-(C2H5)3N mixture, affording (R)-B with 92% ee [321], The olefin, halogen atom, quinoline ring, and ester group are left intact. This product is a key intermediate in the synthesis of L-699,392 (LTD4 antagonist) [323],... 

Potassium tetracarbonylhydridoferrate is a hydride transfer agent that may be used to reduce ketones selectively in high yields (equation 54)205. With diketones a hydroxy ketone is produced. 

Crotyltitanium ate complexes can also be chemoselective 5 is aldehyde selective (98 2), whereas 6 is ketone selective (> 98%). 

Although allyl-arenes are prone to olefin isomerization, several successful reactions have been performed, for example in the chemoselective oxygenation of 22 to aryl-acetone 23 (Table 2) [38]. Allyl alcohols sometimes react sluggishly, but examples with high ketone selectivity are known, for example the oxidation of tertiary alcohol 24 to a-hydroxyketone 25 [39]. 

Unhindered aliphatic ketones selectively yield E-enolates if they are deprotonated by a lithium amide via a transition state structure of type A of Figure 13.15. This occurs, for example, when the B-type transition state is destabilized because of the use of a base that is even more sterically demanding than LDA such as, for example, LTMP (for structure, see Figure 4.18). For example, diethyl ketone and LTMP form the if-enolate with ds = 87 13. 

Bohne, C. (1995) Norrish type I processes of ketones selected examples and synthetic applications, in CRC Handbook of Organic Photochemistry and Photobiology (eds W.M. Horspool and P-.S. Song), CRC Press, Boca Raton, pp. 423-429. 

Upon testing the effect of other ligands at titanium, we came across some unexpected results 90). The amino derivative 102, prepared from 96 and IS, reacts in situ preferentially with ketones. In case of 26 and 82 the 100 101 ratio is 22 78 (Table 3). The in situ reaction of the related compound 104 leads to a 13 87 ratio. By using the ate complexes 106, 108 and 110, the ketone-selectivity turned out to be 4 96, 2 98 and 14 86, respectively ... 

Although a few observations relevant to the mechanism have been made, it is difficult to offer a clear explanation at this time. Initial control experiments indicate that the reactions are kinetically controlled, i.e., they are irreversible under the conditions used. Furthermore, a salt effect is involved, because the distilled amino-titanium compound 102 is essentially non-selective (Table 3). Upon adding MgX2 salts, ketone selectivity increases to 70%. 

Since substituted allyl titanium derivatives (e.g., crotyl) with amino ligands are sterically more demanding than the parent compound, they should display lower degrees of ketone-selectivity. However, this turned out not to be the case. The... 

It is interesting to compare the above results with the reactions of other allyl metal reagents. Whereas allyllithium and allylmagnesium are slightly ketone-selective (Tables 3-5), allylboranes911 as well as certain allylchromium derivatives92)... 

Ate complex with n-BuLi (2). This complex (2) reduces ketones, esters, acid chlorides, and acid anhydrides readily, even at -78°. Consequently, it is useful for selective reduction of these groups in the presence of halide, amide, and nitrile groups, which are inert at low temperatures. It is even possible to reduce a ketone selectively in the presence of an ester group by use of 1 equiv. of reagent at -78°. 

Alkoxy ketones.8 In the presence of ISi(CH3)3 or (CH3)3SiOTf, silyl enol ethers react with a-chloro ethers to give (3-alkoxy ketones selectively. Evidently ISi(CH3)3 activates only the C—Cl bond. Similarly, the reaction of silyl enol ethers with a-chloro sulfides gives rise only to P-alkylthio ketones. 

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