Radicals flanked by the–(alkynyl) Co2 (CO) 6 unit add intramolecularly to carbon–carbon double bonds with unusual stereo-and regioselectivity. Cationic complex 13a (R= CO2Me) reacts with Zn to produce exclusively the trans-5-exo product 14a. Labile propargyl bromide complexes 16a–d, prepared from the alcohols 7a–d, undergo cyclization with Et3B/O2/Ph2SiH2 or upon irradiation. Under the latter conditions atom transfer products ( ...
