1: vinyl-magnesium chloride With zinc(II) chloride in tetrahydrofuran; tert-butyl methyl ether T=-5 - 0°C; 1.25 h; 2: 2,2-Dimethyl-1,3-dioxan-5-one in tetrahydrofuran; tert-butyl methyl ether T=-10 - -5°C; 2.5 h;

in tetrahydrofuran T=0°C; 0.5 h;