AUyl acetates reduction

In several cases the nucleophilic attack on a Tr-allylpalladium complex 97 has been observed to occur on the central carbon atom of the allylic moiety. The resulting paUadacy-clobutane derivative 98, instead of j8-hydride elimination, underwent reductive elimination furnishing a cyclopropane derivative 99. " In spite of theoretical predictions which, appear to rule out such reactions, they have been observed experimentally (Scheme 23). Thus, in the Pd-catalyzed reactions of cyclopropyUdeneethyl acetate 100 with ketene alkyl silyl acetals 101, the spiropentylacetates 103, albeit in low yield, along with the normal products 102 were observed. " With Tj -aUylpaUadium-pyridinylpyrazole complexes 108 as catalysts this reaction mode of aUyl acetates 104 with ketene acetals 105 became predominant so that cyclopropylacetates 106 were obtained as the main products (Scheme 23). An enantioselective version of this cyclopropane formation has also been reported. ... 

Cyclic aUyl carbonates have decreased propensity to equilibrate when compared with acetates. Their reactions are stereochemically cleaner and better defined. Thus, they have been used as stereochemical probes to check the overall stereochemical outcome of the reactions. The formation of the Tf-allylpalladium(II) intermediate occurs with inversion of configuration at the allyl framework. The nucleophilic attack can occur directly on the allylic termini involving a second inversion of configuration (overall retention) or indirectly by previous attachment of the nucleophile to the Pd atom followed by reductive elimination with retention (overall inversion). The reported examples involving cyclic allylic carbonates are in Scheme 10 and Table 1. 

---