copper(l) iodide; ammonium iodide; hydrogen iodide; copper in Petroleum ether 3.5 h;

(R)(S)-1-bromo-1,2-butadiene; lithium; ethylene dibromide 1.) ether, -5 deg C, 2 h, 2.) THF, -78 deg C, 1 h; Yield given. Multistep reaction;