Cyclohexanones reagents

Acetone in conjunction with benzene as a solvent is widely employed. With cyclohexanone as the hydrogen acceptor, coupled with toluene or xylene as solvent, the use of higher reaction temperatures is possible and consequently the reaction time is considerably reduced furthermore, the excess of cyclohexanone can be easily separated from the reaction product by steam distillation. At least 0 25 mol of alkoxide per mol of alcohol is used however, since an excess of alkoxide has no detrimental effect 1 to 3 mols of aluminium alkoxide is recommended, particularly as water, either present in the reagents or formed during secondary reactions, will remove an equivalent quantity of the reagent. In the oxidation of steroids 50-200 mols of acetone or 10-20 mols of cyclohexanone are generally employed. 

When planning the synthesis of a compound using an organometallic reagent or indeed any synthesis the best approach is to reason backward from the product This method is called retrosynthetic analysis Retro synthetic analysis of 1 methylcyclohexanol suggests it can be prepared by the reaction of methylmagnesmm bromide and cyclohexanone... 

Cyclohexanone shows most of the typical reactions of aUphatic ketones. It reacts with hydroxjiamine, phenyUiydrazine, semicarbazide, Grignard reagents, hydrogen cyanide, sodium bisulfite, etc, to form the usual addition products, and it undergoes the various condensation reactions that are typical of ketones having cx-methylene groups. Reduction converts cyclohexanone to cyclohexanol or cyclohexane, and oxidation with nitric acid converts cyclohexanone almost quantitatively to adipic acid. 

The reduction of an asymmetric cyclohexanone (e.g. a steroidal ketone) can lead to two epimeric alcohols. Usually one of these products predominates. The experimental results for the reduction of steroidal ketones with metal hydrides have been well summarized by Barton and are discussed in some detail in a later section (page 76) unhindered ketones are reduced by hydrides to give mainly equatorial alcohols hindered ketones (more accurately ketones for which axial approach of the reagent is hindered " ) are reduced to give mainly axial alcohols. 

The reactions of dichlorocarbene with morpholine and piperidine enamines derived from cyclopentanone and cyclohexanone have been reported to lead to ring expanded and a-chloromethylene ketone products (355,356). Similarly a-chloro-a, -unsaturated aldehydes were obtained from aldehyde derived enamines (357). Synthesis of aminocyclopropanes (353,359) could be realized by the addition of diphenyldiazomethane (360) and the methylene iodide-zinc reagent to enamines (367). 

Common reagents such as lithium diisopropylamide (LDA see Chapter 11, Problem 5) react with carbonyl compounds to yield lithium enolate salts and diisopropylamine, e.g., for reaction with cyclohexanone. 

A second example exploits the fact that the mixed hydride reagent is capable of hydrogenolysis of certain carbon-oxygen bonds. Thus, treatment of cyclohexanone ketal (Chapter 7, Section IX) with lithium aluminum hydride-aluminum chloride results in the rupture of a C-O bond to give the oxyethanol derivative. 

Grignard reagents undergo a general and very useful reaction with ketones. Melhylmagnesium bromide, for example, reacts with cyclohexanone to yield a product with the formula C7HuO. What is the structure of this product if it has an IR absorption at 3400 cm-1 ... 

Triethyl phosphonoacetate, reaction of sodium derivative with cyclohexanone to yield ethyl cvclo hexy lideneacetate, 46, 45 1 nfluoroacetic anhydride, 46, 98 p,0 0 Trifluorostyrene, 47, 52 Trusopropvl phosphite as reagent in dechlorination of decachlorobi 2,4 cyclopentadienyl, 46, 93 1,3,5-Tnketones, from aroylationof 1,3-diketones, 46, 59 from 4-pyrones, 46, 59 Tnmethylamine oxide, reaction with x-octyl iodide to yield octanal, 47, 96... 

As observed with cyclohexanones, the diastereoselectivity of the addition reaction of trimeth-ylaluminum to 2-methylcyclopentanone depends on the stoichiometry of the reactants. Thus, addition of one equivalent of trimcthylaluminum proceeds via preferential tram attack whereas, due to the "compression effect , addition of an excess of the reagent leads to the formation of the equatorial alcohol via predominant attack from the cis side (Table 3)6. In contrast to the addition reactions with trimethylaluniinum, no reversal of the diastereoselectivity upon change of reagent stoichiometry was observed in the addition of triphenylaluminum to 2-methylcyclopentanone6. Even with an excess of the aluminum reagent trans attack predominates. However, the diastereoselectivity is lower than with the use of an equimolar amount of the reactants. 

The conjugate addition of Grignard reagents to 2-cyclohexenone was promoted by catalytic amounts (2-4 mol %) of alkylcopper(I) complexes of the lithium amide prepared from N- (R)-1 -phenylethyl]-2-[(/ )-l-phenylethyliminojcycloheptatrienamine, Li[CuR(CHIRAMT)]52,11. However, 3-substituted cyclohexanones were obtained in very low ee (4-14%). 

Cyclohexanone (5.7 mmol) was added to a solution of the reagent (6.2 mmol) at -78 to -50°C. After 0.5 h at this temperature, it was allowed to warm to ambient temperature over 3 h. The mixture was poured into dilute HC1 (25ml, 0.5m), extracted with dichloromethane (3 x 30ml), and the organic extracts dried and concentrated, to give the epoxysilane (4.7mmol, 83%). 

Primary aliphatic nitro compounds can be reduced to nitriles with sodium dihydro(trithio)borate " or with f-BuN=C/BuN=C=0. Secondary compounds give mostly ketones (e.g., nitrocyclohexane gave 45% cyclohexanone, 30% cyclohexanone oxime, and 19% A-cyclohexylhydroxylamine). Tertiary aliphatic nitro compounds do not react with this reagent. See also 19-41. 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

Littler has studied the oxidation of cyclohexanone with lead(IV), thallium(III), and mercury(II) salts (84), and found that, with all three reagents the rates of oxidation are independent of the concentration of oxidant. Oxidation by thallium(III) and mercury(II) in 35% aqueous perchloric acid showed first-order dependence on [H" ], and Littler suggested that the results were best interpreted in terms of the reaction sequence shown in Scheme 27. The major product of thallium(III) oxidation of... 

Bicyclic keto ester (22) was needed for conformational studies. The common atoms are marked ( ) and the obvious disconnections of this symmetrical molecule require double alkylation of cyclohexanone with a reagent such as (23), Double 1,5-diCO disconnection of (22) is impossible as you will discover if you attempt it. 

Trimethylsilylmethyl Grignard or lithium reagents 1606 add to ketones such as cyclohexanone to give, via the intermediates 1607, the olefins 1608, often in high yields (Scheme 10.5). 

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