Efficient regioselective a-ring functionalization of oestrogens

Complete series of 2-halo- and 2-cyano-oestrogens have been prepared in good to high yields: 2-chloro, 2-bromo, 2-iodo, and 2-cyano derivatives via oestrogen-thallium (III) bis(trifluoroacetate) intermediates, and 2- and 4- fluorooestrogens by direct functionalization using N -fluoropyridinium triflate.