Cycloalkenes to ketones

Oxidation of organohoranes. This oxidant is superior to chromic acid for oxidation of organoboranes derived from cycloalkenes to the corresponding ketones. For example, cyclohexanone is obtained in 81% yield from cyclohexene. 

The oxidation of cycloalkenes to cyclic ketones with PdCl2 is difficult under usual conditions, but allylic oxidation proceeds smoothly. Reaction of cyclohexene with Pd(OAc)2 gives 3-acetoxycyclohexene (81) 1-acetoxycyclohexene (82) is not formed, because no /3-H syn to Pd is available on the acetoxy-bearing carbon, and syn elimination yields the allylic acetate 81 as shown by 80 [39]. 

Unsaturated Ring Ketones.—Acetylene hexacarbonyldicobalt complexes react with ethene, alkenes, and cycloalkenes to provide a general synthetic route to cyclopentenones. Unfortunately most monosubstituted ethenes react non-specifically. 2-Bromoethylallene gives 2-methylcyclopent-2-enone on treatment with Collman s reagent. 

Oxidative reactions frequently represent a convenient preparative route to synthetic intermediates and end products This chapter includes oxidations of alkanes and cycloalkanes, alkenes and cycloalkenes, dienes, aromatic fluorocarbons, alcohols, phenols, ethers, aldehydes and ketones, carboxylic acids, nitrogen compounds, and organophosphorus, -sulfur, -selenium, -iodine, and -boron compounds... 

Strain energies (kcal mol 1) of cyclic ketones and cycloalkenes relative to cycloalkanes from force-field calculations... 

The direct comparison of 1 and 2 in a variety of RCM reactions also indicates a presumably close relationship between these catalysts (Table 1) [6]. Both of them give ready access to cycloalkenes of almost any ring size > 5, including medium sized and macrocyclic products. Only in the case of the 10-membered jasmine ketolactone 16 was the yield obtained with 2a lower than that with lc this result may be due to a somewhat shorter lifetime of the cationic species in solution. However, the examples summarized in Table 1 demonstrate that the allenylidene species 2 exhibit a remarkable compatibility with polar functional groups in the substrates, including ethers, esters, amides, sulfonamides, ketones, acetals, glycosides and even free hydroxyl groups. 

Strained n/d/ -Bredt alkenes as well as -cycloalkenes will undergo [2 + 2] cycloadditions with alkenes. The bridgehead bicyclo[3.3.1]nonenones 16, produced as a transient species by the dehydrobromination of the corresponding bridgehead bromoketone, undergo cycloaddition with 1,1-dimethoxyethenc (15) to give the tricyclic ketones 17 in quantitative yields.7... 

Methyl ketones. Hydrogen peroxide in the presence of Pd(OAc)-. as catalyst converts terminal alkenes to methyl ketones in high yield and with high selectivity (equation I).1 Internal and cycloalkenes are inactive. The actual oxidant is... 

The occurrence of cycloparaffins in nature is limited to petroleums, although unsaturated cycloalkenes and cycloparaffin alcohol ketone derivs are found widely distributed in essential oils. Naphthenes is the term more commonly used than cycloparaffins or cycloalkanes (Ref 3)... 

Isomerization of substituted styrene oxides allows the synthesis of aldehydes in high yields726 [Eq. (5.275)]. Cycloalkene oxides do not react under these conditions, whereas 2,2,3-trimethyloxirane gives isopropyl methyl ketone (85% yield). Isomerization of oxiranes to carbonyl compounds is mechanistically similar to the pinacol rearrangement involving either the formation of an intermediate carbocation or a concerted mechanism may also be operative. Glycidic esters are transformed to a-hydroxy-/3,y-unsaturated esters in the presence of Nafion-H727 [Eq. (5.276)]. 

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