Alkenes into ketones

The Wacker process is an example of a homogeneously catalyzed reaction that occurs in water. The overall reaction involves the conversion of ethylene into acetaldehyde, or terminal alkenes into ketones (Eq. 28). The... 

The overall sequence thus amounts to the conversion of alkenes into ketones and esters. For example ... 

New methods for the conversion of terminal alkenes into ketones RC(0)CH2SePh use the reagent systems PhSeBr-EtOH followed by NaI04, " PhSeBr followed by AgPFe-DMSO, and a one-step process using (PhSe)2-Br2-(Bu3Sn)20. The products are intermediates in further alkylation-deselenation steps which lead to ketones and enones. ... 

Allylic carbonates are most reactive. Their carbonylation proceeds under mild conditions, namely at 50 C under 1-20 atm of CO. Facile exchange of CO2 with CO takes place[239]. The carbonylation of 2,7-octadienyl methyl carbonate (379) in MeOH affords the 3,8-nonadienoate 380 as expected, but carbonylation in AcOH produces the cyclized acid 381 and the bicyclic ketones 382 and 383 by the insertion of the internal alkene into Tr-allylpalladium before CO insertion[240] (see Section 2.11). The alkylidenesuccinate 385 is prepared in good yields by the carbonylation of the allylic carbonate 384 obtained by DABCO-mediated addition of aldehydes to acrylate. The E Z ratios are different depending on the substrates[241]. 

The telomer obtained from the nitromethane 65 is a good building block for civetonedicarboxylic acid. The nitro group was converted into a ketone, and the terminal alkenes into carboxylic acids. The acyloin condensation of protected dimethyl dvetonedicarboxylate (141) afforded the 17-membered acyloin 142, which was modified to introduce a triple bond 143. Finally, the triple bond was reduced to give civetone (144)[120). 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

The use of sofid supports in conjunction with permanganate reactions leads to modification of the reactivity and selectivity of the oxidant. The use of an inert support, such as bentonite (see Clays), copper sulfate pentahydrate, molecular sieves (qv) (151), or sifica, results in an oxidant that does not react with alkenes, but can be used, for example, to convert alcohols to ketones (152). A sofid supported permanganate reagent, composed of copper sulfate pentahydrate and potassium permanganate (153), has been shown to readily convert secondary alcohols into ketones under mild conditions, and in contrast to traditional permanganate reactivity, the reagent does not react with double bonds (154). 

Casey has suggested that the hydrogenation of alkenes by Shvo s catalyst may proceed by a mechanism involving loss of CO from the Ru-hydride complex, and coordination of the alkene. Insertion of the alkene into the Ru-H bond would give a ruthenium alkyl complex that can be cleaved by H2 to produce the alkane [75], If this is correct, it adds further to the remarkable chemistry of this series of Shvo complexes, if the same complex hydrogenates ketones by an ionic mechanism but hydrogenates alkenes by a conventional insertion pathway. 

Burk et al. showed the enantioselective hydrogenation of a broad range of N-acylhydrazones 146 to occur readily with [Et-DuPhos Rh(COD)]OTf [14]. The reaction was found to be extremely chemoselective, with little or no reduction of alkenes, alkynes, ketones, aldehydes, esters, nitriles, imines, carbon-halogen, or nitro groups occurring. Excellent enantioselectivities were achieved (88-97% ee) at reasonable rates (TOF up to 500 h ) under very mild conditions (4 bar H2, 20°C). The products from these reactions could be easily converted into chiral amines or a-amino acids by cleavage of the N-N bond with samarium diiodide. 

Isonitrile insertion into zirconacycles to afford iminoacyl complexes 28 is fast, but rearrangement to q2-imine complexes 30 is slow. In the case of tBuNC, the rearrangement does not occur. Amines 32 are formed on protonolysis of the q2-imine complex. The q2-imine complexes 30 readily undergo insertion of Ti-components (alkenes, alkynes, ketones, aldehydes, imines, isocyanates) to provide a wide variety of products 37 via zirconacycles 36. The overall sequence gives a nice demonstration of how a number of compo-... 

A Co(II) Schiff-base complex converts 1- and 2-alkenes into methyl ketones and the corresponding secondary alcohols in the presence of oxygen or H2O2 in primary alcohol solvent.543 A radical oxidation with cobalt hydroperoxide through the formation and subsequent decomposition of alkyl hydroperoxide was suggested.543 An efficient conversion of alkenylarenes to ketones was achieved by the use of molecular oxygen and EtjSiH in the presence of a catalytic amount of Co(II) porphyrin in 2-propanol.544... 

Alkenes can be transformed into ketones by Wacker oxidation (Entry 2, Table 12.3), but this reaction does not seem to proceed cleanly on polymeric supports. Janda and co-workers were able to oxidize styrenes bound to macroporous polystyrene to the corresponding acetophenones, but reported that the reaction did not proceed on PEG... 

Styrene derivatives can be selectively converted to the corresponding benzyl alcohols by molecular oxygen in the presence of bis(dimethylglyoximato)chloro(pyridine)cobalt(III) and sodium tetrahydroborate (equation 242).559 A likely mechanism for this reaction involves insertion of the alkene into the cobalt-hydride bond, followed by 02 insertion into the cobalt-carbon bond, as in equation (11), and decomposition of the peroxide adduct (168) to the ketone, which is reduced to alcohol by NaBH4 (equation 243). 

Recently, it has been proposed that alkyl hydroperoxides are formed from the Coni-catalyzed Markov-nikov addition of hydrogen peroxide to alkenes.371 The alkyl hydroperoxides thus formed are immediately decomposed into ketones and alcohols under the reaction conditions (equation 237). 

Collins reagent is used for the introduction of carbonyl groups at allylic positions." This transformation of alkenes into enones is much slower than the oxidation of alcohols, requiring a great excess of Cr03 2Py and prolonged reaction times. Consequently, alcohols can be oxidized to aldehydes and ketones by Collins reagent without interference from alkenes. 

Most functional groups resist Collins oxidation, including the oxidation-sensitive sulfides106 and thioacetals.103 Although Collins reagent can transform alkenes into enones" and alkynes into inones,107 these reactions are slower than the oxidation of alcohols into aldehydes or ketones. Therefore, alcohols can be usually oxidized with no interference from alkenes108 or alkynes.109... 

Under oxidation with PCC, migration of alkenes into conjugation with aldehydes or ketones can be avoided by the addition of calcium carbonate (see page 47). 

Migration of alkenes into conjugation with the aldehydes or ketones, produced during the oxidation,... 

A partial migration of an alkene into conjugation with a ketone occurs during a Swern oxidation. The isomerization into conjugation can be purposefully brought about by treat- ... 

Because of the action of Et3N on the activated alcohol, some side reactions—beginning with a deprotonation—can happen in sensitive substrates. For example, a-epimerization of sensitive aldehydes and ketones,260 and migration of alkenes into conjugation with carbonyl groups261 are occasionally found. 

The aluminium alkoxides present in the Oppenauer oxidation can cause some base-induced side reactions. Thus, quite typically during the oxidation of sterols possessing homoallylic alcohols, a migration of the alkene into conjugation with the resulting ketone is observed (see pages 256 and 259).4... 

Full details42 have been published on the conversion of enynes into iminocyclopentenes using a titanium precatalyst in the presence of BuLi and TESCN (equation 9) the resulting iminocyclopentenes can be hydrolysed to cyclopentenones or reduced to allylic silyl-amines. In a related protocol43, the tandem insertion of TMSCN and alkenes, alkynes, ketones or isocyanates into zirconacyclo-pentanes or -pentenes leads to cyclopentylamines carrying an a-alkyl, -alkenyl, -1-hydroxyalkyl or -carboxamide substituent, respectively (equation 9). 

The conversion of an alkene into the corresponding ketone may be effected by means of a convenient sequence which involves hydroboration followed by oxidation with chromic acid of the resulting organoborane (cf. Section 5.4.3,... 

Ketones from halohydrins. Palladium acetate complexed with a triarylphos-phine, particularly tri-o-tolylphosphine, converts halohydrins into ketones in the presence of K2C03. Yields are about 70-85% for substrates in which the halogen is secondary or tertiary, but less than 50% when the halogen is primary because of epoxide formation. The reaction is useful for conversion of alkenes to ketones in those instances in which halohydrins are formed regioselectively. 

Ketone dilithio a,f - and a -dianions have been generated by a tin-lithium exchange reaction of the lithium enolate of /3-tributyltin-substituted ketones.30 A chelation-aided approach, which employs /S-dichlorobutyltin-substituted ketones and n-BuLi, has been used for the generation of ketone a, f) -dianions having the Z-geometry at the alkene. The generated dianions have been transformed into ketones... 

Insertion of alkenes into Os3H2(CO)10 gives compounds of the type Os3H(alkyl)(CO)10 which are usually reactive toward /(-elimination to regenerate alkene (see Section V) or reductive elimination of alkane to allow oxidative addition of the alkene (161,162). Sometimes, however, if the alkene is bi- or polyfunctional, stable insertion products are formed. For example, CH2=CHOMe inserts to give a mixture of diastereomers 71 and 72. Ether coordination reduces the rate of /(-elimination (243). Similar stabilization occurs on inserting a,/(-unsaturated esters (51), although a,/(-unsaturated ketones RCH—CHCOMe (R = H, Me, or Ph) insert, then eliminate the... 

Aqueous chromic acid has been used to oxidize alkylboranes derived from cyclic alkenes to ketones. For example, hydroboration and oxidation of 1-methylcyclohexene converts it into 2-methylcyclohexanone (Equation B2.10). 

Iodylbenzene with catalytic amounts of 2,2-dipyridyl diselenide converted alkenes into allylic ketones directly the actual oxygenating agent was 2-pyridineseleninic anhydride, formed in situ. 

The oxidation of primary and secondary trialkylboranes with pyridinium chlorochromate (PGG) provided aldehydes or ketones.504-507 An oxidative conversion of alkenes into a carbonyl compound was conducted by tandem hydroboration and oxidation with excess A-methylmorpholine-A-oxide (NMO) in the presence of Pr4NRu04 (TPAP) (Equation (105)).508... 

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