Enolates palladium-catalyzed regioselective

The method involves a regioselective, trans-diastereoselective, and enantioselective three-component coupling, as shown in Scheme 7.26. In this case, the zinc enolate resulting from the 1,4-addition is trapped in a palladium-catalyzed allyla-tion [64] to afford trans-2,3-disubstituted cyclohexanone 96. Subsequent palladium-catalyzed Wacker oxidation [82] yields the methylketone 97, which in the presence of t-BuOK undergoes an aldol cyclization. This catalytic sequence provides the 5,6-(98) and 5,7- (99) annulated structures with ees of 96%. 

An alternative method for the preparation of a kinetic zinc ketone enolate (123) from an arene thiol ester 121 and bis(iodozincio)methane (122) in the presence of a palladium(O) catalyst was developed by Matsubara and coworkers (equation 36) . The modest reactivity of the zinc reagent 122 makes this transformation highly chemo- and regioselective neither isomerization of the kinetic enolate 123 nor a palladium-catalyzed coupling with the thiol ester 121 could be observed. Thus, treatment of zinc enolate 123 with various aldehydes or ketones led regioselectively to one aldol product 124. The method provides access to reactive functionalized zinc enolates which are otherwise hard to obtain. 

For Heck reactions catalysed by Pd(OAc)2 associated with dppp, see Ref. [Ig] and (a) Cabri, W., Candiani, I. and Bedeshi, A. (1990) Ligand-controlled a-regioselectivity in palladium-catalyzed arylation of butyl vinyl ether. J. Org. Chem., 55, 3654-5 (b) Cabri, W., Candiani, L, De-Bernardinis, S. et al. (1991) Heck reaction on anthraquinone derivatives ligand, solvent, and salts effects. J. Org. Chem., 56, 5796-800 (c) Cabri, W., Candiani, L, Bedeshi, A. and Santi, R. (1991) Palladium-catalyzed a-arylation of vinyl butyl ether with aryl halides. Tetrahedron Lett., 32, 1753-6 (d) Cabri, W., Candiani, L, Bedeshi, A. et al. (1992) a-Regioselectivity in palladium-catalyzed arylation of acyclic enol ethers. J. Org. Chem., 57, 1481-6 (e) Cabri, W.,... 

Cabri, W., Candiani, L, Bedeschi, A. et al. (1992) Alpha-regioselectivity in palladium-catalyzed arylation of acyclic enol ethers. J. Org. Chem., 57,1481-6. 

Regioselective photocycloaddition of enol carbonate 59 with allene results in the formation of adduct 60 in 83% yield. The protecting group is removed under palladium-catalyzed conditions, and the resulting alcohol undergoes retro-aldol reaction and olefin isomerization to give the 1,5-diketone 62 in excellent yield. This compound contains the AB ring system of the taxane skeleton. 

Scheme 5.11 Regioselective, diastereoselective, and enantioselective palladium-catalyzed allylic alkylation of acylsilanes through thar lithium enolates.

In 1980 Trost and Keinan reported on allylic alkylations of tin enolates such as 33 catalyzed by tetrakis(triphenylphosphine)palladium (equation 12). The stannyl ethers led to a rapid and clean monoaUcylation with high regioselectivity. Thereby, alkylation generally occurred at the less substituted end of the allyl moiety with formation... 

Palladium(0)-catalyzed a-allylations of TMS enol ethers can be carried out cleanly with allylic carbonates. These reactions are highly regioselective, e.g. the mtne- and less-substituted TMS enol derivative of 2-methylcyclohexanone cf. Scheme 37) gave 2-allyl-2-methylcyclohexanone and 2-methyl-6-allylcyclohexanone, respectively. Allylations of aldehyde silyl enol ers occur similarly. Allylations of enol acetates occur with allyl carbonates in the presence of catalytic amounts of palla-dium(0) complexes and tri-n-butyltin methoxide. ... 

Regio- and stereoselective rhodium-catalyzed allylic alkylations of chelated amino add ester enolates have been elaborated. Rhodium complexes in comparison with palladium complexes show a different regioselectivity and have less tendency to isomerize (Scheme 19). ... 

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