Cyclohexanone elimination reaction

For instance, 2-methylpropene reacted with acetic acid at 18°C in the presence of Al-bentonite to form the ester product (75). Ion-exchanged bentonites are also efficient catalysts for formation of ketals from aldehydes or ketones. Cyclohexanone reacted with methanol in the presence of Al-bentonite at room temperature to give 33% yield of dimethyl ketal after 30 min of reaction time. On addition of the same clay to the mixture of cyclohexanone and trimethyl orthoformate at room-temperature, the exothermic reaction caused the liquid to boil and resulted in an almost quantitative yield of the dimethyl ketal in 5 min. When Na- instead of Al-bentonite is used, the same reaction did not take place (75). Solomon and Hawthorne (37) suggest that elimination reactions may have been involved in the geochemical transformation of lipid and other organic sediments into petroleum deposits. 

Most photodecarbonylation reactions of cyclic ketones, especially in the vapor phase, have been postulated to proceed from various vibrational levels of excited singlet states.321 However, the elimination reaction leading to unsaturated aldehydes has now been shown to occur largely via excited triplet states. In solution, where the lowest vibrational levels of the excited states are rapidly reached, to-alkenals are the major products observed in both photolysis and radiolysis of cyclopentanone and cyclohexanone. The reaction is quenched by oxygen and dienes,322-324 as well as by the alkenal produced in the reaction.325 The reaction is also sensitized by benzene triplets.322,323 With cyclopentanone, quenching by 1M piperylene occurs some 20 times as fast... 

The Wittig reaction is very useful. How else could we convert cyclohexanone into pure methylenecyclohexane We can use the reactions of this chapter to devise a different synthesis. Some thought might lead to a sequence in which cyclohexanone reacts with methyllithium to give, after hydrolysis, a tertiary alcohol. An acid-catalyzed elimination reaction would give some of the desired product, but there is no easy way to avoid the predominant formation of the imdesired isomer, 1-methylcy-... 

Another method for the hydrogenoiysis of aryl bromides and iodides is to use MeONa[696], The removal of chlorine and bromine from benzene rings is possible with MeOH under basic conditions by use of dippp as a ligand[697]. The reduction is explained by the formation of the phenylpalladium methoxide 812, which undergoes elimination of /i-hydrogen to form benzene, and MeOH is oxidized to formaldehyde. Based on this mechanistic consideration, reaction of alcohols with aryl halides has another application. For example, cyclohex-anol (813) is oxidized smoothly to cyclohexanone with bromobenzene under basic conditions[698]. 

The lithium enolates of cyclopentanone and cyclohexanone undergo addition-elimination to the 2,2-dimethylpropanoic acid ester of ( )-2-nitro-2-hepten-l-ol to give 2-(l-butyl-2-nitro-2-propenyl)cycloalkanones with modest diastereoselection. An analogous reaction of the enolate ion of cyclohexanone with the 2,2-dimethylpropanoic acid ester of (Z)-2-nitro-3-phenyl-2-propenol to give 2-(2-nitro-l-phenyl-2-propenyl)cyclohexanones was also reported. The relative configuration of these products was not however determined6. 

Ono and coworkers have extended the radical elimination of v/c-dinitro compounds to P-nitro sulfones151 and P-nitro sulfides.138,152 As P-nitro sulfides are readily prepared by the Michael addition of thiols to nitroalkenes, radical elimination of P-nitrosulfides provides a useful method for olefin synthesis. For example, cyclohexanone is converted into allyl alcohol by the reaction shown in Eq. 7.110. Treatment of cyclohexanone with a mixture of nitromethane, PhSH, 35%-HCHO, TMG (0.1 equiv) in acetonitrile gives ahydroxymethylated-P-nitro sulfide in 68% yield, which is converted into the corresponding allyl alcohol in 86% yield by the reaction with Bu3SnH.138 Nitro-aldol and the Michael addition reactions take place sequentially to give the required P-nitro sulfides in one pot. 

The trimethylsilyl ethers 212 of four-membered 1-alkenyl-1-cyclobutanols rearrange to the ring-expanded 0-mercuriocyclopentanones 213. These can be converted into the a-methylenecyclopentanones 214 through elimination or further expanded by one-carbon atom into cyclohexanones 215 via the Bu3SnH-mediated free radical chain reactions [116]. A similar radical intermediate is suggested to be involved in the ring expansion of a-bromomethyl-fi-keto esters [117]. (Scheme 84)... 

Scheme 33 illustrates the difference in reactivity between triazolines obtained from cyclohexanone and cyclo-pentanone enamines. Thus, the reactions of azidophosphonates 239 with cyclohexanone enamines produce unstable aminotriazolines 240 that cannot be isolated due to their spontaneous elimination of amines to provide triazoles 241. Contrary to that, triazolines 242, derived from cyclopentanone enamines, are isolated in good yield (76-88%) and cannot be converted to the corresponding triazoles even by thermolysis <1995H(40)543>. Probably, introduction of a double bond between two five-membered rings would involve too much molecular strain. 

All reactions were stirred at speeds in excess of 500 rpm to eliminate any effects due to stirring rate (17). Initially, polymerizations were conducted at 60 C in cyclohexanone solution. When 18-crown-6 was used as the catalyst, little difference was observed in the presence or absence of sodium bisulfite. 

The cyclohexanone phenylhydrazone (512), obtained by reacting cyclohexanone (510) with phenylhydrazine (511), on indolization, furnished tetrahydrocarbazole 513 which, on dehydrogenation, afforded carbazole 514. The success of the reaction is dependent on the reagent used for indolization and the dehydrogenating agent. The mechanism for the formation of the tetrahydrocarbazole involves a tautomeric equilibrium and the formation of a new C-C bond via a [3,3]-sigmatropic rearrangement followed by elimination of ammonia (495,496,498) (Scheme 5.7). 

For example, the reaction of 3-chlorocyclohexanone with DBU in toluene gives a product which is seen to have two vinyl protons by NMR and thus is an elimination product, probably either A or B. Now while one might rationalize by both chemical intuition and by the splitting pattern that conjugated isomer A is the product, examination of the IR spectrum shows a carbonyl group (at 1680 cm-1) and an olefin band (at 1630 cm-1). A typical cyclohexanone comes at 1710 cm-1 and cyclohexene comes at 1643 cm-1. 

Pyridinealdehyde yields pyridine and some dipyridyl, a reaction which proceeds without destruction of the heterocyclic ring 19). Ketones decarbon-ylate equally well. Benzophenone and dibenzoyl form diphenyl in high yields 2°). Several interesting eliminations have been found for cyclic and bi-cyclic ketones. In the case of cyclohexanone the decarbonylation accounts for only a small proportion of the reaction products. Benzoquinone decarbon-ylates to cyclopentadienone in good yields 20K Under the reaction conditions this compound dimerizes and decarbonylates again. 

As the Wittig reaction forms both tt and cx-bonds, the disconnection is right across the middle of the alkene giving a choice of starting materials. So with the exo-cyclic alkene 26, very difficult to make by elimination methods, we could use formaldehyde or cyclohexanone as the carbonyl component with either phosphonium salt 25 or 28. It is a matter of personal choice whether you draw the ylid, the phosphonium salt or the alkyl halide at this stage. 

In the second part of the reaction of Figure 12.24, the a-palladated cyclohexanone E decomposes (since it is an alkylpalladium(II) compound with a syn-H atom in the position /3 to the metal) to an alkene, namely the previously mentioned unsaturated ketone B, and to H-Pd-Cl. In Chapter 16 this type of reaction will be repeatedly encountered in connection with the keyword /3-hydride elimination as A —> B in the Figures 16.13 and 16.14 and as step 7 of Figure 16.35 (part II). H-Pd-Cl decomposes according to the equation H-Pd-C1 —> Pd(0) + HC1, which describes a reductive elimination. Reductive eliminations will be... 

---