Conjugate Allylation of Cyclic α,β-Unsaturated Esters

Abstract

The conjugate allylation of a homologous series of a,bunsaturated cyclic esters 8-10 by addition of diallylcuprate (method A), fluoride ion catalyzed addition of trimethylallylsilane (method B), and aluminium tris(2,6-diphenylphenoxide) (ATPH)-mediated addition of allyllithium (method C) was investigated. Method A was not selective in all cases. For methods B and C an influence of ester moiety and ring size on the regioselectivity was observed. Methyl cyclopentenoate 8c gave mainly the 1,2/1,2-product regardless the allylation method while tert-butyl and benzyl ester moieties favored the 1,4-products. For larger rings 9, 10 and the anellated system 19 methods B and C behave complementary depending on the ester function: Method B gave best results of 1,4-addition products for benzyl esters while method C worked better for tert-butyl esters.