1: 1,4-cyclohexanedione monoacetal With lithium hexamethyldisilazane in tetrahydrofuran T=-78°C; 0.566667 h; 2: methyl iodide in tetrahydrofuran T=-78 - 20°C; 2.33333 h;

lithium iodide in N,N-dimethyl-formamide T=130°C; 6 h;

1: ethyl 8-hydroxy-1,4-dioxaspiro[4.5]dec-7-ene-7-carboxylate With N,N,N',N',N'',N''-hexamethylphosphoric triamide; tert.-butyl lithium; sodium hydride in tetrahydrofuran; pentane T=-78°C; 0.166667 h; 2: methyl iodide in tetrahydrofuran; pentane T=-78 - 25°C; 5 h; 3: With potassium hydroxide in ethanol 8 h; Heating;

1: 1.) NaH / 1.) benzene, DMF, RT, 1 h, 2.) benzene, DMF, RT, 2 h 2: 86 percent / LiI / dimethylformamide / 6 h / 130 °C View Scheme

1.1: 33 g / NaH / tetrahydrofuran / 5 h / Heating 2.1: NaH; t-BuLi; HMPA / tetrahydrofuran; pentane / 0.17 h / -78 °C 2.2: tetrahydrofuran; pentane / 5 h / -78 - 25 °C 2.3: 10 percent aq. KOH / ethanol / 8 h / Heating View Scheme

Multistep reaction;

toluene-4-sulfonic acid in acetone