1) H3C-Br + Mg = H3C-MgBr (X1);
2) H3C-MgBr + H3C-CH2-CHO = H3C-CH2-CH(O-MgBr)-CH3 (X2);
3) H3C-CH2-CH(O-MgBr)-CH3 + HBr = H3C-CH2-CH(OH)-CH3 (X3) + MgBr2;
4) H3C-CH2-CH(OH)-CH3 + CuO (+T) = H3C-CH2-C(O)-CH3 (бутанон) + Cu + H2O;
5) H3C-CH2-C(O)-CH3 + HCN = H3C-CH2-C(OH)(CN)-CH3 (X4).