1: (E)-4-ethoxy-4-oxobut-2-enoic acid With pivaloyl chloride; triethylamine in tetrahydrofuran T=-10°C; 1 h; 2: oxazolidin-2-one With lithium chloride in tetrahydrofuran T=20°C; 5 h; Further stages.;

methylmagnesium bromide; hydroquinone in tetrahydrofuran T=0 - 20°C;