Allyl carbonates, reduction

Diphenylketene (253) reacts with allyl carbonate or acetate to give the a-allylated ester 255 at 0 °C in DMF, The reaction proceeds via the intermediate 254 formed by the insertion of the C = C bond of the ketene into 7r-allylpalla-dium, followed by reductive elimination. Depending on the reaction conditions, the decarbonylation and elimination of h-hydrogen take place in benzene at 25 °C to afford the conjugated diene 256(155]. 

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]... 

Nitrocycloalkanones can be successfully C-allylated by Pd(0)-catalyzed reaction with various allyl carbonates and 1,3-dienemonoepoxides under neutral conditions, as shown in Eqs. 5.56 and 5.57, respectively.801 The product of Eq. 5.56 is converted into cyclic nitrone via the reduction of nitro group with H2-Pd/C followed by hydrolysis and cyclization.80b... 

Methylmagnesium N-cyclohexyliso-propylamide, 189 By oxidation at an allylic carbon Selenium dioxide, 272 By reduction of a,0-unsaturated carbonyl compounds Sodium borohydride, 278 Sodium dithionite, 281 Other methods r-Butyllithium, 58 Butyllithium-Potassium f-butoxide,... 

A good route to 2-C-allyl (and hence by reduction, C-alkyl) derivatives of ascorbic acid involves the interaction of L-ascorbic acid with allyl acetates or allyl carbonates in the presence of Pd(0) catalyst.355... 

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... 

Our first approach to 1 is based on a retrosynthetic analysis depicted in Fig (8). The crucial step to construct the cw-fused bicyclic ring skeleton of 1 is the intramolecular allylic amination of a cw-allylic carbonate 25. The paUadium-catalyzed allylation takes place with retention of the configuration [76] and requires the c/s-isomer 25 for the ring closure. Compound 25 may be derived from keto acid 24 through a sequence of reactions including esterification, O-methoxycarbonylation, removal of the Boc and benzylidene groups, dehydrative cyclization, reductive alkylation and ureido formation. The last five transformations are to be conducted in a successive manner, i.e., without isolation of the intermediates. The 4-carboxybutyl chain of 1 may be installed by the reaction of O-trimethylsilyl (TMS) cyanohydrin 23 with a di-Grignard... 

A six-membered cyclic allylic carbonate 102 undergoes a palladium-catalyzed decarboxylative C-C bond cleavage to afford dienic carbonyl compound 104 [122]. Decarboxylation of the allylic carbonate moiety provides the driving force for production of the intermediate five-membered hetero-palladacycle 103, from which formal reductive cleavage takes place. 

In a first example of cyclopropane formation from allylpalladium complexes the reaction of dimeric 7t-allylpalladium chloride (1, R = H) with the enolate of methyl cyclohexanecarboxylate (2) was found to give the normal allylic alkylation product 3 only in low yields ( 20%) if the reaction was carried out in tetrahydrofuran in the presence of triphenylphosphane at room temperature, whereas with triethylamine in hexamethylphosphoramide the cyclopropane product 4 is formed in 70% yield. Deuterium labelling of the allyl moiety indicates that the reaction proceeds via nucleophilic attack of the enolate at the central allylic carbon followed by reductive elimination of the cyclopropane product. 

The 1,4-conjugate addition of triorganoindium to enones is promoted by a catalytic amount of Ni(COD)2 (Scheme 8.71) [100], Allylindium reagents can be used in Pd-catalyzed cross-coupling reaction with aryl halides (Scheme 8.72). The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 8.73) [101]. The indium-mediated palladium-catalyzed Ullmann-type reductive coupling of aryl halides proceeds in aqueous media under air (Scheme 8.74) [102]. 

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