1.1: lithium diisopropyl amide / tetrahydrofuran / 0.5 h / -78 °C / |Inert atmosphere 1.2: 48 h / 20 °C / |Inert atmosphere 2.1: CpCr(CO)3H / benzene-d6 / 50 °C / |Inert atmosphere View Scheme

2,2'-azo-bisisobutyronitrile; tris-(trimethylsilyl)silane in carbon dioxide T=80°C; carbonylative cyclization; P=174812 Torr; 5 h;