Syntheses with organoboranes. XIII. Synthesis of ω-(4-bromophenyl)alkanoic acids and their borylation

Abstract ω-(4-Bromophenyl)alkanoic acids 2c – e were obtained from 1-bromo-4-alkenylbenzenes 5c – e by hydroboration–thermal isomerization–oxidation. Their esters 11c – e were transformed in good yields into the corresponding boronates 12c – e by the cross-coupling reaction with 4,4,5,5,4′,4′,5′,5′-octamethyl[2,2′]bi[[1,3,2]dioxaborolanyl] ( 10 ) in an ionic liquid, [bmim][BF 4 ]. The use of pinacolborane for the coupling reaction in the ionic liquid gave debromination products, and low yields of 12c – e . Ethyl 3-(4-bromophenyl)propanoate ( 7c ) was transformed into ethyl 3-(4-[1,3,2]dioxaborolanyl)propanoate ( 9c ) by the cross-coupling with [2,2′]bi[[1,3,2]dioxaborinanyl].