Resolution allyl anion

Resolution (enantiomers), 307-309 Resonance, 43-47 acetate ion and, 43 acetone anion and. 45 acyl cations and, 558 allylic carbocations and, 488-489 allylic radical and, 341 arylamines and, 924 benzene and, 44. 521 benzylic carbocation and, 377 benzylic radical and, 578 carbonate ion and. 47 carboxylate ions and, 756-757 enolate ions and, 850 naphthalene and, 532 pentadienyl radical and. 48 phenoxide ions and, 605-606 Resonance effect, 562 Resonance forms, 43... 

The use of a metal catalyst, such as palladium, also provides for some asymmetric induction when an allylic system is treated with a stabilized anion (Scheme 22.13)82-103 or with other nucleophiles.82,87,104-111 This approach also allows for the kinetic resolution of allyl acetates.104,112... 

Hua has used the products of Pauson-Khand cycloadditions for syntheses of optically active pental-enene and racemic pentalenolactone E methyl ester. The racemic ketone in the first case was converted to the necessary optically active intermediate by kinetic resolution via 1,4-addition of an optically active allyl sulfoxide anion. These represented the first synthesis of natural products containing the angularly fused triquinane skeleton from bicyclic Pauson-Khand products (equation 53 and Scheme 20). ... 

The lipase-catalysed enantioselective acylation of allylic alcohols in an ionic liquid solvent was demonstrated by Itoh et al. [16] (Fig. 7.7). They found that the acylation rate was strongly dependent on the counter anion of the imidazolium salt, while the lipase-catalysed acylation proceeded with high enantioseleclivity in all ionic liquid tested. Good results were obtained when the reaction was carried out in [bmimT [PFg ] or [bmun" ][BF ]. Other examples of kinetic resolution of allylic alcohols catalysed by lipases in ionic liquids were also reported by these authors [71, 72]. The transesterification of 5-phenyl-l-penten-3-ol under reduced pressure at 27 hPa and 40°C was carried out using methyl phenylthioacetate as acyl donor in [bmim+] [PF ] and [bdmim ][BF ], for obtaining the corresponding acylated compound in optically pure form [71], The acetylation of methyl mandelate catalysed by immobilised P5L in [bdmim ][BF ] is another example reported by these authors about the successful application of ionic liquids as reaction media in racemic resolutions... 

Optically active barbiturates important in pharmacy, are obtained by classical synthesis and resolution procedures [14]. A new approach to the synthesis of optically active barbiturates is enantioselective catalysis with Pd complexes. An example is shown in Scheme 10 on the right side. The synthesis of the enantiomers of a N-methyl barbiturate containing a quaternary asymmetric carbon atom is achieved by allylation of the corresponding precursor with allyl acetate. Pd/triphenylphosphine complexes are efficient catalysts for this reaction which give a racemic mixture of the product. The reaction proceeds via a jt-allyl complex of Pd as an intermediate (Scheme 10, left side). This 7t-allyl complex is attacked by the nucleophile, the anion of N-... 

A remarkable kinetic resolution was observed recently by Feringa and coworkers when 2-silyloxyfuran was reacted with the racemic unsymmetrical allylic substrate 86, catalyzed by the palladium complex of Trost s ligand (/ ,/ )-14, as illustrated in Scheme 5.28. The acetate anion liberated upon oxidative addition of palladium(O) is assumed to cleave the silyl protecting group, so that the enolate anion forms aside from TMSOAc. After allylic alkylation of that enolate, double bond migration leads to butenolide (R)-87 isolated in 47%, if the reaction was run with 52% conversion. Not only the product 87 but also the recovered acetate... 

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