Palladium(0)-catalyzed allylation of 2,2′-dihydroxybiphenyl by 1-ethenyl-cyclopropyl sulfonates:: Preparation of 2,2′-bis(cyclopropylideneethoxy) biphenyls

Dipotassium salts of 2,2'-dihydroxybiphenyl derivatives underwent palladium(0) catalyzed regioselective allylation by sulfonic esters (mesylates, tosylates) of 1-ethenylcyclopropanol to produce, in good yields, 2,2'-bis(cyclopropylideneethoxy)biphenyls, which are of biological interest. Whilst the tetrapotassium salt of 2,2',6,6'-tetrahydroxybiphenyl, formed the triadduct 2,2'-tris(cyclo-propylideneethoxy)hydroxybiphenyl as its main product. An unexpected palladium-induced rearrangement of the monoadducts 2-(2-cyclopropylideneethoxy)-2'-hydroxybiphenyl derivatives into the 2-[2-(1-ethenylcyclopropyloxy)]-2'-hydroxybiphenyl derivatives occurred; while the minor diastereomer of the monoadduct 2[(2-cyclopropylidene-1-trimethylsilyl)ethoxy]-6,6-dimethoxy-2'-hydroxybiphenyl upon standing in CDCl3, underwent Claisen rearrangement into the 2,2'-dihydroxy-6,6'-dimethoxy-3-(2-tri-methylsilylethenyl)cyclopropylbiphenyl.