1: tert-butyl 5-[(trimethylsilyl)oxy]-3,4-dihydropyridine-1(2H)-carboxylate; tert-butyl 5-[(trimethylsilyl)oxy]-3,6-dihydropyridine-1(2H)-carboxylate With methyllithium in tetrahydrofuran T=-15°C; 0.666667 h; 2: trifluoroacetic anhydride in tetrahydrofuran T=-78°C; 1.5 h;