Scheme 8.
Synthesis of macrocycle via formation of Se−C bond between Sec and indole ring (approach (A)) and synthesis of macrocycle containing the selenylated indole via amide bond (approach (B)), conditions: (a) RB (Rose Bengal) (0.1 equiv.), LED460, MeCN; (b) HOBt (1 equiv.), EDC (1.5 equiv.), DMF.