1: tetrahydrofuran; diethyl ether / 14 h / -78 - 20 °C / Inert atmosphere 2: trifluoroacetic acid / water / 3 h / 0 - 20 °C 3: 200 °C / Inert atmosphere View Scheme

1: trifluoroacetic acid / water / 3 h / 0 - 20 °C 2: 200 °C / Inert atmosphere View Scheme

1: toluene-4-sulfonic acid / toluene / 8 h / Reflux 2: tetrahydrofuran; diethyl ether / 14 h / -78 - 20 °C / Inert atmosphere 3: trifluoroacetic acid / water / 3 h / 0 - 20 °C 4: 200 °C / Inert atmosphere View Scheme

T=200°C; Inert atmosphere;