1: tert-butyl 3-azabicyclo[3.1.0]hexane-3-carboxylate With sec.-butyllithium; (-)-sparteine in diethyl ether; cyclohexane T=-78°C; 38 h; Inert atmosphere; 2: carbon dioxide in diethyl ether; cyclohexane T=-68°C; 0.05 h;