Ketone reaction with lithium

The reactions of A -steroids with nitrosyl fluoride parallel those of their A -isomers. Thus, 17 -acetoxyandrost-4-ene (37) is converted to the nitrimine (38), in 67 % yield and thence to the 4-ketone (39), which can be dehydrofluorinated to the A -4-ketone (40) with lithium bromide in di-methylformamide. In the corresponding 19-nor series the nitroso dimer is also formed. 

Ai -A-homo-4-ketones by reaction with lithium and biphenyl at The resulting dienone is transformed into the corresponding tropone by treatment with bromine. The Swiss chemists also found that base treatment of 19-mesyloxy-A " -3-oximes gives directly 4-oximino-A-homo-estra-l(10),2,4a-trienes in moderate yield. ... 

A ketone vvith a substituent group in its /3 position might be prepared by a conjugate addition of that group to an a,/3-unsaturated ketone. In the present instance, the target molecule has a propyl substituent on the /3 carbon and might therefore be prepared from 2-methyl-2-cyclopentenoneby reaction with lithium dipropylcopper. 

Keller (1998) describes the semi-continuous reaction process of a vinyl ketone K with lithium acetylide LA to yield lithium ethinolate LE an intermediate in the vitamin production. In an undesired side reaction an oligomer byproduct BP is produced. During the process, reactant K is fed to the semi-batch reactor at a rate to maximize the selectivity for LE. 

Treatment of the acetylenic ketones 186 with lithium dialkylcuprates and trapping the resultant enolates with acetic anhydride produced the enyne-allene 187 (Scheme 20.39) [72], Regeneration of the oxyanion-substituted enyne-allene system using methyllithium at -20 °C led to the formation of either the indanones 188 or the ben-zofluorenones 189 through a Schmittel cyclization reaction. 

Stereoselectivity in reductions of acyclic oximes depends on the configuration of C=N bond. ( )-Isomer of oxime 89 produced syn-hydroxylamine 90 in excellent stereoselectivity in reaction with phenyldimethylsilane-trifluroacetic acid while giving anti-product in the reaction with lithium aluminium hydride. Stereoselectivity in reductions of (Z)-isomers of 89 was substantially lower in both cases (equation 62) . It can be assumed that the rules of stereoselectivity established in diastereoselective reduction of ketones can be applied to reduction of oximes as well. 

Esters or ketones. (S)-2-Pyridylthioates can be converted by reaction with lithium dialkylcuprates in ether at —78° into either esters or ketones. The former products are obtained without contamination by ketones if the reaction is conducted under oxygen ketones arc formed when the reaction is conducted under nitrogen. Yields of bolli products are generally in the range 70-95%.<>... 

Mukaiyama found that Lewis acids can induce silyl enol ethers to attack carbonyl compounds, producing aldol-like products.22 The reaction proceeds usually at -78 °C without selfcondensation and other Lewis acids such as TiCl4 or SnCI4 are commonly used. The requisite silyl enol ether 27 was prepared by treatment of ketone 13 with lithium hexamethyl disilazide (LiHMDS) and trapping the kinetic enolate with chlorotrimethylsilane. When the silyl enol ether 27 was mixed with aldehyde 14 in the presence of BF3-OEt2 a condensation occurred via transition state 28 to produce the product 29 with loss of chlorotrimethylsilane. The induced stereochemistry in Mukaiyama reactions using methylketones and a, -chiral aldehydes as substrates... 

Cycloadditiom. This reaction provides an enantioselective synthesis of a cyclooctane-containing terpenoid (5). The optically active precursor (3) was obtained by reduction of the r-alkyl alkynyl ketone 1 with lithium aluminum hydride... 

Similar to the case for its reaction with lithium aluminum hydride, an ester reacts with a Grignard or organolithium reagent to produce a ketone as the initial product. But because the ketone also reacts with the organometallic reagent, an alcohol is the final product. The mechanism for this reaction is shown in Figure 19.10. Note the similarities between this mechanism and that shown in Figure 19.7 for the reduction of an ester with lithium aluminum hydride. 

The reaction is rapid even at low temperature and is generally carried out at — 78 °C. The kinetic enolates are produced from unsymmetrical ketones under these conditions and the phenylseleno group is introduced at the less substituted position usually with high regio- and diastereoselectivity. Thus, the reaction of tricyclic ketone 11 with lithium diisopropylamide followed by reaction with phenylselenenyl chloride gives a mixture of a-selenenylated enones 12 in 3 1 ratio9 . 

Synthesis of giycidic esters. The Darzcas reaction fails with compounds such as acetaldehyde which give only self-condensation products. Borch has described a new procedure which is generally applicable. The a-bromo ester anion (2) is smoothly generated by reaction with lithium bis(trimethylsilyl)amide in THF at —78". Addition of the aldehyde or ketone at — 78° followed by workup aflbrds the corresponding... 

Synthesis of ketones. Stork and Maldonado have disclosed a new synthesis of ketones from aldehydes RCHO- RCOR. The aldehyde is first converted into the cyanohydrin and then the hydroxyl group is protected by reaction with ethyl vinyl ether to give (1). This is then converted into the anion by reaction with lithium diiso-propylamide under carefully controlled conditions. The base is generated from butyl-lithium and diisopropylamine in THF and then (1) in hexamethylphosphorie triamide... 

An interesting synthesis of silyl enol ethers involves chain extension of an aldehyde. Aldehydes are converted to the silyl enol ether of a ketone upon reaction with lithium (trimethylsilyl)diazomethane and then a drrhodium catalyst. Initial reaction of lithium(trimethylsilyl)diazomethane [LTMSD, prepared in situ by reaction of butyllithium with (trimethylsilyl)diazomethane] to the aldehyde (e.g., 37) gave the alkoxide addition product. Protonation, and then capture by a transition-metal catalyst, and a 1,2-hydride migration gave the silyl enol ether, 38. 

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