1: 1-chloro-1,2,2-trimethylcyclobutane With bromine; magnesium in diethyl ether 2 h; Heating; 2: carbon dioxide in tetrahydrofuran T=0°C; 2 h;

1.1: NaH / xylene / 90 °C / 3.5 Torr 1.2: 88 percent / xylene / 3 h / 60 °C 2.1: 44 percent / HCl gas / pentane / 3 h / -78 °C 3.1: Mg; Br2 / diethyl ether / 2 h / Heating 3.2: tetrahydrofuran / 2 h / 0 °C View Scheme

1.1: 44 percent / HCl gas / pentane / 3 h / -78 °C 2.1: Mg; Br2 / diethyl ether / 2 h / Heating 2.2: tetrahydrofuran / 2 h / 0 °C View Scheme

lithium diisopropyl amide 1.) THF/pentane, RT, 30 min, 2.) methyl iodide, RT, 3 h; Yield given. Multistep reaction;