Aryl lead derivatives, reaction with 8-ketoesters

The reaction of 4-indolyllead triacetate 12 was explored with a number of /3-ketoesters in a study directed toward the total synthesis of welwistatin D (Scheme 3).26 However, while the model ketone derivatives 13 and 15 could be arylated in high yields with lead reagent 12 to give 14 and 16 respectively, the reaction with the more highly substituted welwistatin precursor 17 failed, probably because of the steric hindrance imposed by the methyl and vinyl substituents. 

The reactions of arylation of heterocyclic /3-ketoesters were employed in the synthesis of a number of isoflavanones and isoflavones.27,28 cr-Methylene cr-arylketones can be easily and selectively obtained by arylation of allyl /3-ketoesters which are eventually deprotected by the Tsuji s procedures. a Deallyloxycarbonylation was performed by treatment of the allyl cr-aryl-/3-ketoesters with catalytic amounts of palladium(n) acetate, triethylammo-nium formate and triphenylphosphane in THF at room temperature and afforded the a-arylketones in 75-97% yield.27 Deallyloxycarbonylation-dehydrogenation can be realized with the same allyl esters by treatment with catalytic amounts of palladium(n) acetate and l,2-bis(diphenylphosphino)ethane (DPPE) in acetonitrile under reflux and affords the ct-aryl cr,/3-unsaturated ketones in 60-90% yield (Scheme 4).28 In particular, this reaction was used in a direct convergent synthesis of 2 -hydroxyisoflavones involving arylation of an appropriate allyl /3-ketoester with the MOM-protected (2-methoxymethoxyphenyl)lead triacetate derivative (Scheme 4). The reaction of the isomeric... 

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