1: With n-butyllithium; diisopropylamine in tetrahydrofuran; hexane T=-78°C; 0.5 h; 2: 3,5-difluoropyridine in tetrahydrofuran; hexane T=-78°C; 1.5 h; 3: tributyltin chloride in tetrahydrofuran; hexane T=-78 - 20°C; 2 h;