SCHEME 4.

Synthesis of key starting material 8 (route 2). aReagents and Conditions. a. Amberlyst 15/Lewatit S100, 15–30 °C; b. Electrochemical oxidation, MTBS, 1 atm

Synthesis of key starting material 8 (route 2). aReagents and Conditions. a. Amberlyst 15/Lewatit S100, 15–30 °C; b. Electrochemical oxidation, MTBS, 1 atm