Stereocontrol in nickel mediated syntheses of cyclobutabenzenes. The selective preparation of cis and trans derivatives of 7,8-dibromocyclobutabenzene

Article abstract of DOI:10.1016/S0040-4020(97)10219-8

Most α,α,α',α'-tetrabromo-o-xylenes that are substituted at the ortho and meta positions yield, upon applying nickel mediated cyclization conditions, the respective trans-7,8-dibromocyclobutabenzenes derivatives as major products. However, when the ortho substituent is an ester or an amide, a good stereochemical control can be achieved by running the reactions with or without the presence of phosphines. The bromine atom at the 7 position can be substituted specifically with inversion by methoxy, yielding the 7-Br-8-OMe respective cyclobutabenzene, that can be reacted in a stereospecific Diels-Alder reaction to form the cis-bromo-methoxy-tetrahydronaphthalene derivative.