1: 1,1-dibromo-3-methylprop-1-ene With n-butyllithium in diethyl ether; hexane T=-78°C; 1 h; 2: dimethyl(phenyl)silyl chloride in diethyl ether; hexane T=0°C; 0.25 h; Further stages.;

tetrabutyl ammonium fluoride in N,N-dimethyl-formamide T=80°C; 1 h;