Asymmetric alkoxycarbonylation

Asymmetric 1,4-addition reactions, boron reagents, 10, 388 Asymmetric Alder-ene reactions, characteristics, 10, 579 Asymmetric alkoxycarbonylation, characteristics, 11, 467 Asymmetric alkylations, with alkylzincs, 2, 403 Asymmetric allylation... 

Palladium complexes bearing chiral monodentate phosphine ligands 592 (R = H, Ph) are effective catalysts for asymmetric alkoxycarbonylation of allyl phosphates <1997TL8227>. 

Diphosphines have a richer heritage in asymmetric catalysis than monophosphines, which is believed to be a result of the more rigid conformations of the complexes that they form. Many attempts have been made to tune the steric and electronic characteristics of this class of ligand to optimize their catalytic performance in asymmetric alkoxycarbonylation. 

Abstract The use of Co building block in presence of water or an alcohol to functionalise alkenes by hydroxycarbonylation or alkoxycarbonylation reactions is reviewed in this chapter. The hydroxyl groups can be present in the substrate itself so cascade reactions can occur. Palladium precursors are largely involved in these reactions and this analysis of the literature focuses on the mechanisms involving Pd(0), Pd(H)(X)L2, PdX2 and an oxidant like CuCl systems. Introduction of chiral L or L2 ligands or even the presence of chiral carbon atoms in the substrate lead to asymmetric carbonylation reactions. 

Under oxidation conditions, a C—C double bond can be functionalized by either two alkoxycarbonyl groups or one alkoxycarbonyl group and one heteroatom. As shown in Scheme 4.14, two ester groups are successfully introduced to styrene in an enantioselective manner, producing a phenylsuccinic ester using a Pd/MeO-BIPHEP complex. mcw-Diols are converted into cyclic ethers in an asymmetric manner when catalyzed by Pd/chiral bisoxazoline. Intramolecular aminopallada-tion followed by carbomethoxylation gives an cyclic amino ester in moderate ee when catalyzed by a Pd/bis(isoxazoline) complex. " ... 

Ukaji and co-workers employed bis(oxazoline) ligands in the asymmetric bis(alkoxycarbonylation) reaction of homoallylic alcohols. One example of this reaction, the conversion of homoallylic alcohol 200 to its carbonylation product 201, is illustrated in Figure 9.58. This reaction proceeded in 78% yield with an ee of 50%. 

Asymmetric hydrogenation-based processes using a highly active and stereoselective catalyst generate relatively little waste. The asymmetric hydrogenation of readily preparable a-hydroxycarbonyl- or tz-alkoxycarbonyl-suInstituted enamrdes has frequently been applied to the preparation of unnatural a-amrno acids with a wide variety of side chains since the successful application of L-Dopa (Scheme 9.4) [13h]. 

The precise origin of the stereoselectivity in these reactions is not known at present. The acyl mechanism has generally been assumed, rather than the alkoxycarbonyl one (see Section 61.2.5.8) and it seems reasonable that asymmetric induction must have taken place prior to or during the CO insertion reaction. A review of asymmetric carbonylation is available.579... 

Optically active 4-alkoxycarbonyl-3-hydroxycyclohexanones (formed in highly enantio- and diastereoselective organocatalytic asymmetric domino Michael aldol reaction of / -keto esters and a,/ -unsaturated ketones) are transformed into corresponding chiral oxepanones under the action of urea-hydrogen peroxide and trifluoroacetic anhydride <2004AGE1272>. 

Oxidative alkoxycarbonylation asymmetric carbonylation, 11, 467 catalyst development, 11, 467 mechanism, 11, 466 Oxidative amination, olefins, 10, 155 Oxidative cleavage, mechanisms, 1, 103 Oxidative promoters, in Pauson-Khand reaction with dicobalt octacarbonyl, 11, 337... 

V-Alkoxycarbonyl- and /V-carboxamido-oxaziridines (35) have been developed as reagents capable of converting aromatic alkenes into epoxide, aziridine, or hydrooxidation products, in ratios depending on the oxaziridine structure. Chiral oxaziridines can effect epoxidation and hydrooxidation with promising levels of asymmetric induction.48... 

The reactivity of 47/-benzopyran-4-ones in Diels-Alder reactions is well documented <1987T3075>, and recently high asymmetric induction has been achieved in the reaction of 3-alkoxycarbonyl-substituted chromones with chiral auxiliaries and Danishefsky s diene <1991JOC2058>. It should be noted that 3-formylchromones can react as heterodienes in the stereoselective inverse electron Diels-Alder reaction with enol ethers <1994T11755> to provide a route to pyrano[4,3-A][l]benzopyrans a heterocyclic nucleus which occurs naturally in the fungal metabolite fulvic acid <1984CC1565>. The thermal Diels-Alder reaction of 477-pyran-4-one 405 in the presence of an excess of Danishefsky s diene 404 provided cycloadduct 406 (Equation 32) <1996H(43)745>. 

Incidentally, cyclopropanation, one of the carbon-carbon bond formation reactions, is a useful reaction by using diazo compounds to give a variety of keto or alkoxycarbonyl cyclopropane derivatives, for example, crythantimates and their analogues as popular insectsides [2]. The cyclopropanation reactions have often been carried out with the use of copper or rhodium catalysts however, this results in stereochemical problems of trans-cis selectivity or asymmetric induction [3]. 

Some optically active 3-alkoxycarbonyl-2-methylisoxazolidines were obtained by asymmetric decomposition in the presence of catalytic amount of Pd-BINAP complex. For instance, the kinetic resolution of racemic 105 by 106 afforded (+)-105 in 48% yield and with... 

Under forcing conditions, alkyl aryl ethers are cleaved by Grignard reagents by displacement of aryloxide [A]. Such reactions are not generally useful in synthesis, but the displacement of methoxide from positions ortho to alkoxycarbonyl [2] and oxazolinyl groups [3] has been applied to the synthesis of orffco-substituted carboxylic acids, and displacement ortho to diphenylphosphino groups has also been reported [4], The following example describes the key step in a synthesis of anthraquinones. Recently, asymmetric induction by a chiral oxazolinyl substituent has been reported [5] ... 

Enders D, Oberborsch S (2002) Asymmetric Mannich reactions with a-silylated trimethylsilyl enol ethers and IV-alkoxycarbonyl Imines. Synlett 2002 471-473... 

Phenylalanine derivatives with various nitrogen substituents R1 and R2 (30) were prepared and their a-methylation was examined (Table 3.2). It turned out that derivatives with an alkoxycarbonyl group on the nitrogen undergo a-methylation with modest asymmetric induction (entries 5-7). The presence of two substituents on the nitrogen seems to be essential for asymmetric induction (entries 1 vs. 7). 

Very few examples of asymmetric 1,4-induction are reported in connection with the addition of acidic Ti complexes to chiral y-alkoxycarbonyl compounds. According to the Cram model, the chelation is expected to afford a flexible seven-membered ring intermediate, resulting in less efficient induction (equation 34). An early example of asymmetric 1,4-induction is provided by the reaction of o-phthalal-dehyde (96 equation 35) with 2 equiv. of MeTi(OPr )3 which affords an 83 17 molar mixture of racemic- 97) and meso-(98), whereas Ae analogous reaction with MeMgl leads to a 1 1 mixture of the above diastereomers. 

---