Hydroesterification asymmetric

So far, very little work has been carried out on asymmetric carbonylation. Existing studies all concern the hydroesterification of alkenes (equation 145). Depending on the structure of the alkene and the regioselectivity of the reaction, one or two asymmetric carbon atoms may be present in the product (equation 145).S74... 

Much higher enantiomeric excesses have been achieved in the hydroesterification of a-methyl-styrene.90-91 In this case, the asymmetric center is generated by hydrogen addition at the tertiary site. Tlie reaction is sensitive to the alcohol, the highest enantiomeric excesses being obtained with isopropanol or r-butanol (equation 60). 

Other approaches that have been suggested include catalytic asymmetric hydroformylation of 2-methoxy-6-vinylnaphthalene (6) using a rhodium catalyst on BINAPHOS ligand followed by oxidation of the resultant aldehyde 7 to yield 5-naproxen (Scheme 6.3).22 However, the tendency of the aldehyde to racemize and the co-generation of the linear aldehyde isomer make the process less attractive. Other modifications related to this process include catalytic asymmetric hydroesterification,23 hydrocarboxylation,24 and hydrocyanation.25... 

Other Asymmetric Reactions. Asymmetric synthesis using the new ligand 1 is still limited. When 1 is used for Pd-clay catalyzed hydroesterification of styrene with carbon monoxide and, ... 

Palladium-catalyzed hydroesterification of styrene gives predominantly the branched ester, in which a new chiral center has b n created at the 2-position (equation 34). Carrying out this reaction at low pressure (1-2 bar) in the presence of the bulky chiral phosphine neomenthyldiphenylphosphine and tri-fluoroacetic acid leads to significant asymmetric induction (50% ee) this work seems to represent the only significant advance towards stereocontrol of catalytic hydroesterification reactions. 

Asymmetric induction in the palladium-catalyzed hydroesterification of z-methylstyrene, styrene and other alkenes in the presence of ligands with rigid 5//-dibenzophospholyl units linked to chiral cyclobutane, dioxolane or cyclohexane skeletons (CBDBP, DIPHOL, CHDBP) is compared with the effect of the analogous diphenylphosphane ligands18 23. 

Asymmetric hydroesterification of styrenes is suggested as an alternative route to optically active 3-arylbutanoic acids, a series of nonsteroidal anti-inflammatory drugs18. Thus, with palladium(0)bis(dibenzylideneacetone) in the presence of NMDPP and trifluoroacetic acid 6-methoxy-2-vinylnaphthalene gives the pharmaceutically interesting methyl (— )-2-(6-methoxy-2-naphthvl)propanoate (naproxen) with 42% ee20. 

Hydroesterification of A-vinylphthalimide with PdC l2(PPh,h or palladium(II) chloride in the presence of (-)-Diop, (-)-DlPHOL, DIOCOL, NMDPP. PAMP. and DIPAMP and other chiral mono- and diphosphanes results in only low asymmetric induction in the branched product2 -31. 

Especially noteworthy is the field of asymmetric catalysis. Asymmetric catalytic reactions with transition metal complexes are used advantageously for hydrogenation, cyclization, codimerization, alkylation, epoxidation, hydroformylation, hydroesterification, hydrosilylation, hydrocyanation, and isomerization. In many cases, even higher regio- and stereoselectivities are required. Fundamental investigations of the mechanism of chirality transfer are also of interest. New chiral ligands that are suitable for catalytic processes are needed. 

Hydroesterification of alkynes proceeds smoothly using PdCl2(PPh3)2 as a standard catalyst, offering a convenient synthetic method of a, jS-unsaturated esters 1. Carbonylation of 1-alkynes and asymmetric alkynes yields a mixture of regioisomers. 

An enantioselective version of this reaction to form carboxylic acids and esters would certainly be valuable. Examples of asymmetric hydrocarboxylation of norbomene have been published with significant selectivities, but asymmetric hydroesterification of vinylarenes have been less successful. No examples of these reactions that occur in high yields and with enantioselectivities over 90% have been reported. ... 

The cationic paUadium(II) complex [Pd(MeCN)2(PPh3)3](BF4)2 is an active catalyst for the hydroesterification of styrene using CO and methanol under very mild conditions. The catalytic system, Pd(Oac)-PPh3-p-toluenesulfonic (p-TsOH) could also produce the branched ester regioselectively in excellent yield at ambient temperature. The catalytic asymmetric hydroesterification of styrene by the use of chiral phosphines, such as (5)-l-[(l )-r,2-bis(diphenylphosphino)ferrocenyl]ethyldimethylamine, and (5)-(i )-BPPFA as ligands (Eq. 19). ... 

Hayashi T, Tanaka M, Ogata I. Palladium-catalyzed asymmetric hydroesterification of alpha-methylstyrene by use of chiral dibenzophospholes as ligands. Tetrahedron Lett. 1978 3925-3926. 

Wang L, Kwok WH, Chan ASC, Tu T, Hou X, Dai L (2003) Asymmetric hydroesterification of styrene using catalysts with planar-chiral ferrocene oxazoline ligands. Tetrahedron Asym 14 2291-2295... 

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