Allyl ketone

The enamine 315 as a carbon nucleophile reacts with 7r-allylpalladium complexes to give allyl ketones after hydrolysis[265],... 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

The reductive coupling of the 7r-allylpalladium enolates 679 gives the allylated ketones. This reaction is also possible thermally, as the Carroll reaction, which... 

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

Some examples of conjugate addition reactions of allylic silanes are given in Scheme 9.5. Entries 1 to 3 illustrate the synthesis of several (3-allyl ketones. Note that Entry 2 involves the creation of a quaternary carbon. Entry 4 was used in the synthesis of a terpenoid ketone, (+)-nootkatone. Entry 5 illustrates fluoride-mediated addition using tetrabutylammonium fluoride. These conditions were found to be especially effective for unsaturated esters. In Entry 6, the addition is from the convex face of the ring system. Entry 7 illustrates a ring closure by intramolecular conjugate addition. 

Allyl Ketones from Imidazolides and Allyl Titanium(IV) Compounds... 

Imidazolides are useful for the conversion of allyl titanium compounds into allyl ketones 963... 

Because in the case of a sterically crowded imidazolide the formation of a carbinol is more difficult, reaction with the titanium reagent or the corresponding Grignard compound produces the allyl ketone in about the same yield [96]... 

Reactions of a,(3-unsaturated acylzirconocene chlorides with stable carbon nucleophiles (sodium salts of dimethyl malonate and malononitrile) at 0°C in THF afford the Michael addition products in good yields (Scheme 5.38). Direct treatment of the reaction mixture with allyl bromide in the presence of a catalytic amount of Cul -2LiCl (10 mol%) in THF at 0 °C gives the allylic ketone in a one-pot reaction. This sequential transformation implies the electronic nature of a,P-unsaturated acylzirconocene chloride to be of type E as shown in Scheme 5.37. 

Acyclic and cyclic allylic ethers and acetals react normally with dihalocarbenes at the C=C bond [e.g. 77, 85, 108,114,121,122], Carbene insertion into the C=C bond of allylic ketones, which can be complicated by competitive reaction by the carbonyl group, can also be effected via the initial formation of the acetal and has been used in the synthesis of cyclonona-3,4- and -4,5-dienones from cyclooctenones [125],... 

The same catalytic system (SeOi/TBHP) has also been used by Chabaud and Sharpless in the allylic oxidation of alkynes. The oxidation products resulting from the Se02-catalyzed allylic oxidation with TBHP are the allylic alcohol, the allylic diol, the allylic ketone, the ketol and the enynone (Scheme 127). The main product of the reaction is either the alcohol or the diol, depending on the substrate employed (together 76-100% of the whole yield). The yields of allylic oxidation products together range from 15 to 88%. From the observed results with unsymmetrical alkynes it could be concluded that the reactivity sequence for the carbon attached to the triple bond of alkynes is CH2 CH > CH3. 

Sheldon and coworkers have developed chromium-substituted molecular sieves (CrAPO-5) as recyclable solid catalysts for several selective oxidations, among them also the allylic" and benzylic ° " ° " ° oxidations using TBHP or O2 as the terminal oxidants (equation 63), which yielded the corresponding benzylic ketones in moderate yield (conv. 13-70%) and moderate to good selectivity (41%, 65-97%). The benzylic alcohols were formed as side products. Allylic oxidation also proceeded with good conversions, while selectivities were lower and both possible products, the allylic ketone (31-77% selectivity) and the allylic alcohol (0-47% selectivity), were formed. Chromium sUicalite showed activity for selective benzylic oxidation in the presence of TBHP as well as giving mainly the allylic ketone (2-cyclohexen-l-one with 74% selectivity) and the allylic alcohol as minor product (2-cyclohexen-l-ol with 26% selectivity) -. ... 

The enantioselective a-allylation of a ketone has become increasingly important. Martin Hiersmann of the Technische Universitat Dresden reports (Tetrahedron Lett. 2004,45, 3647) that a-ketoesters readily form enol ethers, such as 6. On exposure to an enantiomerically-purc Cu catalyst, the enol ethers undergo facile Claisen rearrangement, leading to the allylated ketone (e.g. 7) with high enantiomeric... 

Considerable use has also been made of allyl carbonates as substrates for the allylation of Pd enolates.9 The reaction of Pd° complexes with allyl enol carbonates119,120 proceeds by initial oxidative addition into the allylic C—O bond of the carbonate followed by decarboxylation, yielding an allylpalladium enolate, which subsequently produces Pd° and the allylated ketone (equation 22). In like fashion, except now in an intermolecular sense, allyl carbonates have been found to allylate enol silyl ethers (equation 23),121 enol acetates (with MeOSnBu3 as cocatalyst) (equation 24),122 ketene silyl acetals (equation 25)123 and anions a to nitro, cyano, sulfonyl and keto groups.115,124 In these cases, the alkoxy moiety liberated from the carbonate on decarboxylation serves as the key reagent in generating the Pd enolate. 

Ketoacids126,127 form the same intermediates as the allyl 3-ketoesters by nucleophilic addition of the carboxylate to a n-allylpalladium complex. Decarboxylation generates the allylpalladium enolate, which again yields Pd° and allylated ketone. Enol silyl ethers have also been employed with allyl arsenites93 to provide allylated ketones. 

Substituted 2-(/J-oxoalkyl)tetrahydrofurans have been prepared in acceptable yields by a one-step aldol-type reaction of allyl ketones and 4-methyl-l-phenyl-4-penten-l-one, catalyzed by a rhodium(I) complex-tin(II) chloride mixture (equation 180)652. This type of catalyst mixture has also been used for both linear653 and cyclic654 codimers in a similar fashion. 

Although simple ketones and esters can not be allylated by Pd catalysts, they are allylated with allyl carbonates via their enol ethers of Si and Sn. In the allylation of the silyl enol ether 202 with allyl carbonate 200, transmetallation of 202 with the n-allylpalladium methoxide 201, generated from allyl methyl carbonate (200), takes place to generate the Pd enolates 203 and 204. Depending on the reaction conditions, allyl ketone 205 is formed by the reductive elimination of 203 [100]. When the ratio of Pd Ph3P is small, the a,/i-unsaturated ketone 206 is obtained by -elimination [101]. For example, the silyl enol ether 208 of aldehyde 207 is allylated with allyl carbonate (200) to give a-allylaldehyde 210 via 209. The a-allyl carboxylate 213 is obtained by allylation of ester 211 with allyl carbonate (200), after conversion of ester 211 to the ketene silyl acetal 212 [102], As the silyl group is trapped in these... 

Allyl ketones can be prepared by trapping acylpalladium intermediates with main group metal compounds. The allyl ketone 251 can be prepared from the allyl ester 248 by trapping acylpalladium 249 with the alkylzinc compound 250 at room temperature and 1 atm [115]. Reaction of geranyl chloride (252) with the furylstannane 253 under CO pressure afforded the ketone 254, which was converted to dendrolasin (255) [93]. Aldehydes are prepared by trapping with a metal hydride. The /l,y-unsaturated aldehyde 257 is prepared by the carbonylation of the allyl chloride 256 in the presence of Bu3 SnH [116,117],... 

The reductive coupling of the 7i-allylpalladium enolates 400 gives the allylated ketones 403. This reaction is also possible thermally and is called the Carroll reaction. Whereas the Carroll reaction proceeds by heating up to 200 °C, the Pd-catalysed Carroll-type reaction can be carried out under mild conditions (even at room temperature) by reductive elimination of the 7t-allylpalladium enolate 400 [177,178], The Pd-catalysed reaction is mechanistically different from the thermal reaction and more versatile, which is explained by the [3,3] sigmatropic rearrangement of the enolate form. For example, thermal Carroll rearrangement of the a,a-disubstituted keto ester 410 is not possible, because there is no possibility of the enolization. However, it rearranges to ketone 411 smoothly with the Pd catalyst, via the 7i-allylpalladium enolate. 

The formation of the allyl ketone 421 is explained by the following mechanism. The Ru alkynyl complex 423, formed by oxidative addition, isomerizes to the Ru vinylidene complex 424. Nucleophilic attack of allyl alcohol to the electron-deficient. vp-carbon of 424 generates the allyloxycarbene complex 425, which is converted to... 

After reaction of the excess lithium with isoprene the enolate is alkylated with allyl bromide diastereoselectively from the less hindered face, opposite to the axial methyl group at the bridge head, to provide allyl ketone 3 as the single diastereomer. 

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. 

Propargyl and allyl ketones can be cyclised into furans using AUCI3 (0.1mol%) in acetonitrile 18... 

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