Ir-Allylpalladium complexes regioselectivity

Regioselectivity in the Addition of Soft Carbon Nucleophiles to ir-Allylpalladium Complexes 627... 

Stereocontrol (vide infra) can be efficiently engineered in the addition of acetate to ir-allylpalladium complexes (equation 49).168-171 The regioselective addition of acetate of allylpalladium complexes to prepare y-acetoxy-( )-a,0-unsaturated esters172 and y-acetoxy-a.P-unsaturated sulfones has also been achieved (equations 50 and 51).173-174... 

The nature of the ligands on the palladium in ir-allyl complexes can influence the regioselectivity exhibited by soft carbon nucleophiles. ir-Allylpalladium complexes generated from methylenecycloalkanes provide an example of the effect of ligands on regiochemistry. The complexes derived from methylene-cyclopentane and methylenecycloheptane both exhibit exclusive exocyclic addition by the anion of methyl(methylsulfonyl) acetate with triphenylphosphine ligands on the Pd (equation 223). In contrast, the complex derived from methylenecyclohexane yields a 62 38 ratio of exocyclic endocyclic addition (equation 226). 

Addition of MeMgl158 or PhLi160 to ir-allylpalladium complexes derived from methylenenoibomane exhibits selective C—C bond formation at die more hindered allyl terminus. Soft carbon nucleophiles with the same allyl species show the opposite regioselectivity (equation 252).158,160... 

All of the various sulfur nucleophiles that have been studied, including PhSCh—, RS— and (Et0)2P(0)S—, have been demonstrated to add to ir-allylpalladium complexes by ligand addition. Interpretation of the regioselectivities of these nucleophiles must be tempered by the realization that the allyl— SChPh, -SR and -SP(0)(0Et)2 products are capable of isomerization by means of reentering the ir-allylpalladium manifold. 

The reaction of CO with ir-allylpalladium complexes shows highly regioselective insertion into the less substituted allyl terminus235 237-239 as illustrated in equations (295M297). One interesting exception is shown in an allyl complex possessing a Cl group on its terminus, where insertion takes place into the more substituted allyl end (equation 298).234... 

Isocyanide insertion into ir-allylpalladium complexes generally occurs regioselectivity into the less substituted allyl terminus (equation 300).240... 

The regioselectivity of the insertion of 1,3-dienes into ir-allylpalladium complexes possesses two components. First, with respect to the allyl unit, the insertion takes place at the more substituted termin-us.248 249,251,252 Second, with regard to the diene it has been shown that 2-substituted-1,3-dienes insert at the more substituted alkene.248 249 These interesting features have been explained by the intermediacy of an n -allyl species which is bound to the palladium at the less substituted terminus and with the Pd com-... 

An elegant example of a stereo relay in a nonrigid system employed a chiral vinyl lactone 430 For the relay to be completely successful (i) the ionization of the vinyl lactone must occur from one conformation, (ii) the intermediate ir-allylpalladium complex must retain its stereochemistry, and (iii) the nucleophile must attack regioselectively at the carbon of the allyl system distal to the incipient carboxylate. This distal transfer of chirality was achieved as shown in equation (346). This same process has been utilized in a synthesis of an optically active vitamin E side chain from D-glucose.431... 

It is well known that ir-allylpalladium complexes (86) are easily formed by the reaction of PdCb with P. y-unsaturated esters or ketones (85). An attempted oxidation of. y-unsaturated esters and ketones with the PdCl2/CuCl/02 catalyst system in aqueous DMF led to ir-allylpalladium complex formation as the main reaction, and the oxidation of the alkenic bond was hardly observed to a significant extent. However, in aqueous dioxane or THF, the oxidation became the main reaction, giving y-keto esters and 1,4-diketones (87), respectively, with high regioselectivity (Scheme 26).Some results are shown in Table 2. In all cases, no P-keto ester or 1,3-diketone was detected. At the end of the reaction, formation of a considerable amount of the ir-allylpalladium complex (86) was observed. y-Keto esters and 1,4-diketones are useful intermediates for Ae preparation of cyclopentanedione and cyclopentenone, respectively, by base-catalyzed cyclization. Tliis regioselective oxidation provides a unique and efficient synthetic method for y-keto ester and 1,4-diketone synthesis. 

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