1: methyllithium; 2-bromo-3-methyl-2-cyclopenten-1-one in tetrahydrofuran T=-78°C; 2 h; 2: With tert.-butyl lithium in tetrahydrofuran T=-78°C; 2 h; 3: formaldehyd; methyl iodide With p-methylbenzenesulfonyl (tosylate); sodium hydride more than 3 stages;

Multistep reaction;