Scheme 4.
Photoisomerization of 4 a–d and 5 to obtain 16 a–d and 17. For 4 a, 16 a: R1=phenylethynyl; 4 b, 16 b: R1=(p‐methoxyphenyl)ethynyl; 4 c, 16 c: R1=(2‐thiophenyl)ethynyl; 4 d, 16 d: R1=(p‐dimethylaminophenyl)ethynyl; 5, 17: R1=phenyl.
Photoisomerization of 4 a–d and 5 to obtain 16 a–d and 17. For 4 a, 16 a: R1=phenylethynyl; 4 b, 16 b: R1=(p‐methoxyphenyl)ethynyl; 4 c, 16 c: R1=(2‐thiophenyl)ethynyl; 4 d, 16 d: R1=(p‐dimethylaminophenyl)ethynyl; 5, 17: R1=phenyl.