3.3- Dimethyl-cyclohexanone

Johnson and Whitehead have further shown that the reductive elimination of the pyrrolidine group from the pyrrolidine enamine of 2,4-dimethyl-cyclohexanone (16), which involved treating it with a mixture of lithium aluminum hydride and aluminum chloride (9), gave the trans isomer of 3,5-dimethyl-/l -cyclohexene (17) which on subsequent hydrogenation on a platinum catalyst led to the // onr-3,5-dimethylcyclohexane (18). 

Analog liefert Cyclohexanon in 70°/oiger Ausbcute 2,6-Dimethyl-cyclohexanon Aliphatische und aromati-sche Aldehyde alkylieren auch den Indol-Ring in 3-Stellung unter ahnlichen Bedingungen4. 

Before the emergence in the mid-1980s of the asymmetric deprotonation of cA-dimethyl cyclohexanone using enantiomerically pure lithium amide bases, few reports pertaining to the chemistry of these chiral reagents appeared. Although it is not the focus of this chapter, the optically active metal amide bases are still considered to be useful tools in organic synthesis. Readers are advised to consult the appropriate literature on the application of enantiomerically pure lithium amides in asymmetric synthesis.6... 

DIMETHYL CYCLOHEXANONE-2,6-DICARBOXYLATE (Cyclohexanone-2,6-dicarboxylic acid, dimethyl ester)... 

Figure 1. Natural Products Synthesized from (S)-3-Hydroxy-2,2-dimethyl cyclohexanone... 

The fact that the initial cleavage is reversible has been long suspected from the fact that the quantum yield for Norrish Type I products never approaches one, even for very reactive ketones. Positive evidence for the back reaction was provided by Barltrop, who showed that Type I cleavage of cis-2,3-dimethyl-cyclohexanone is accompanied by its isomerization to hmy-2,3-dimethylcyclo-hexanone.87... 

Excellent enantioselectivity was achieved for the transfer hydrogenation of pinacolone by using (S)-25a as a catalyst with 2-propanol in the presence of (CH3)2CHONa to give the S alcohol in >99% ee (Scheme 28) [90], 2,2-Dimethyl-cyclohexanone was reduced with the same catalyst with 98% optical yield. Reduction of cyclohexyl methyl ketone with (S)-25b gave the S alcohol in 66% ee. 

House and Fischer (38) have found that lithium dimethyl cuprate reacts with enone 108 and yields a mixture of trans and cis 3,5-dimethyl-cyclohexanones 109 and 110 in a 98 2 ratio. Similar results were observed by Allinger and Riew (39) using methylmagnesium iodide in the presence of copper(I) chloride. In another case, Heathcock and co-workers (AO) observed the exclusive formation of the trans isomer V[2 from enone 111 no cis isomer was detected. Thus, the preferred mode of approach by cuprate reagent is also 76 + 78 which leads to a chair-like enolate ion. 

A pressure increase, brought about by an increase in the concentration of the ketone or by the addition of an inert gas, enhances the formation of the unsaturated aldehyde as compared to that of CO. The value of awehyde increases at the expense of 0co> thus, the ketone consumption yield is independent of pressure. This seems to be generally valid in the photolysis of the cyclic ketones it was confirmed, for instance, for cyclopentanone °, cyclohexanone 2-methyl cyclohexanone and 2,6-dimethyl cyclohexanone . An increase in wavelength also favours the formation of the aldehyde as compared to decarbonylation in the photolysis of cyclobutanone , cyclopentanone and cyclohexanone . At 3130 A, the decrease in temperature has a similar effect on the product distribution in the photolysis of cyclopentanone , cyclohexanone , 2-methyl cyclohexanone , and 2,6-dimethyl cyclohexanone to that caused by the increase in wavelength or pressure. However, at shorter wavelengths, the quantum yields seem to be independent of temperature . ... 

Wittig reactions in the solid slate of the inclusion compound of 4-methyl- or 3,5-dimethyl-cyclohexanone and an optically active host with carbethoxymethylenetriphenylphosphorane gave optically active alkenes (50) and (51) with optical purities in the range 5-60%.3 8... 

Problem 2. 12 What product would you expect from a mixed Claisen-like reaction of 2,2-dimethyl cyclohexanone with diethyl oxalate (Practice Problem 23.4) ... 

An illustration of this behavior is provided in equation (1). A 67 33 mixture of the less- and more-substituted potassium enolates was produced upon treatment of 2-methylcyclohexanone with tritylpotassium in DME. However, the major product of alkylation of this mixture with methyl iodide was 2,2-dimethyl-cyclohexanone and significant amounts of tri- and tetra-methylcyclohexanone were also obtained. ... 

Scheme V. Raphael s first route to strigol. Conversion of 2,2-dimethyl cyclohexanone to hydroxy lactone 17.

The enolate salts of simple ketones react with aryllead reagents, but the reaction is of little practical value. Indeed, only trisubstituted a-carbon atoms are reactive. The case of the potassium enolate of cyclohexanone derivatives is significant no reaction with cyclohexanone enolate (78), 36% with the mixture of enolates of 2-methylcyclohexanone (79), and 75% in the case of 2,6-dimethyl cyclohexanone enolate (80). ... 

Interligand asymmetric induction. Group-selective reactions are ones in which heterotopic ligands (as opposed to heterotopic faces) are distinguished. Recall from the discussion at the beginning of this chapter that secondary amines form complexes with lithium enolates (pp 76-77) and that lithium amides form complexes with carbonyl compounds (Section 3.1.1). So if the ligands on a carbonyl are enantiotopic, they become diastereotopic on complexation with chiral lithium amides. Thus, deprotonation of certain ketones can be rendered enantioselective by using a chiral lithium amide base [122], as shown in Scheme 3.23 for the deprotonation of cyclohexanones [123-128]. 2,6-Dimethyl cyclohexanone (Scheme 3.23a) is meso, whereas 4-tertbutylcyclohexanone (Scheme 3.23b) has no stereocenters. Nevertheless, the enolates of these ketones are chiral. Alkylation of the enolates affords nonracemic products and O-silylation affords a chiral enol ether which can... 

S)-(+)-3-Hydroxy-2,2-dimethyl cyclohexanone Cyclohexanone, 3-hydroxy-2,2-dimethyl-, (S)- (11) (87655-21-8)... 

Kenji Mori and Hideto Mori 56 YEAST REDUCTION OF 2,2-DIMETHYL-CYCLOHEXANE-1,3-DIONE (S)-(+)-3-HYDROXY-2,2-DIMETHYL-CYCLOHEXANONE... 

Cyclohexanone added to magnesium methyl carbonate prepared from Mg, methanol, and COg in dimethylformamide (cf. Synth. Meth. 14, 709), refluxed 2 hrs. under Ng, treated at ca. 0° with satd. methanolic HCl, and allowed to stand overnight at room temp. dimethyl cyclohexanone-2,6-dicarboxylate. Y 44-45%. S. N. and M. Balasubrahmanyan, Org. Synth. 49, 56 (1969). 

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