Biradicals from thermolysis of N-[2-(1-alkynyl)phenyl]-N '-phenylcarbodiimides and their subsequent transformations to 6H-indolo[2,3-b] quinolines

Thermolysis of the carbodiimide 9a in gamma-terpinene at 138 degrees C prod uced 2-(phenylamino)quinoline (11a, 49%) and the parent 6H-indolo[2,3-b]qui noline (14a, 16%). Apparently. 11a was produced via the biradical 10a follo wed by hydrogen-atom abstraction from gamma-terpinene. A two-step biradical pathway through 12a or a one-step intramolecular Diels-Alder reaction coul d furnish 13a, which then underwent tautomerization to give 14a. With the c arbodiimide 9b having a trimethylsilyl substituent at the acetylenic termin us, thermolysis in refluxing p-xylene at 138 degrees C produced the 6H-indo lo[2,3-b]quinoline 14b (86%) exclusively. Treatment of 14b with 6 N NaOH in refluxing ethanol then furnished 14a in 92% yield. Similarly, the 6H-indol o[2,3-b]quinolines 14c-f were obtained from thermolysis of the carbodiimide s 9c-f. The use of the aza-Wittig reaction between 4-methoxyphenyl isocyana te and the iminophosphoranes 2d and 2f to produce the corresponding carbodi imides followed by thermolysis furnished the 6H-indolo[2,3-b]quinolines led and 16f having a methoxy substituent at the C-2 position. Thermolysis of t he carbodiimides 25a and 25b produced 26a and 26b having two indoloquinolin e units connected at the 11 and 11' positions with either a three-carbon or a five-carbon tether. Using 1,4-phenylene diisocyanate for the aza-Wittig reaction with 2 equiv of the iminophosphorane 2g followed by thermolysis fu rnished 31 (66%) having two indoloquinoline units incorporated in the seven fused rings.