1: 6,6-dimethyl-4,8-dioxaspiro[2,5]oct-1-ene With N,N,N',N',N'',N''-hexamethylphosphoric triamide; n-butyllithium in tetrahydrofuran; hexane T=-70°C; 0.833333 h; 2: 1,4-diiodobutane in tetrahydrofuran; hexane T=-70 - -50°C; 8 h; Further stages.;

1: 1) NaNH2, 2) NH4Cl / liq. NH3, Et2O 2: 1) BuLi, hexamethylphosphoric triamide (HMPA), 2) HMPA / 1) THF, -70 deg C, 2) THF, -70 to -40 deg C, 6.5 h View Scheme