1: in tetrahydrofuran T=-5°C; 0.5 h; 2: With 2,3-dicyano-5,6-dichloro-p-benzoquinone in tetrahydrofuran T=20°C; 2 h;

1: 85 percent / TBAF; isopropyl acetate / tetrahydrofuran / 20 °C 2: 87 percent / isopropyl acetate / tetrahydrofuran / 1 h / 20 °C 3: 4.55 g / DBU; isopropyl acetate / 1 h / 70 °C 4: 94 percent / PPh3; CO / Pd(OAc)2 / acetonitrile / 12 h / 70 °C / 4560 Torr View Scheme