Synthesis and Stereoisomerization of Intra- and Intermolecularly Bridged Indigo

Abstract
The intramolecularly bridged N,N′-azelaoylindigo (3) and N,N′-sebacoylindigo (4) have been synthesized from indigo and the corresponding dichloride. The intermolecularly bridged N′,N″-sebacoylbis(N-acetylindigo) (5) has been synthesized from N-acetylindigo and sebacoyl dichloride. The relative rates of the cis-to-trans thermal isomerization of 3, 4, and 5, compared with that of N,N′-diacetylindigo (1c), were as follows: 3, 0.77; 4, 3.9; 5, 1.4; 1c, 1.0.