Waste-Free Synthesis of Condensed Heterocycles

Significance

Reported is a so-called waste-free synthesis of substituted 8-isocoumarin derivatives or 4-ethenylcarbazoles from the same starting materials - acetylenes and 2-amino- (and 2-hydroxy-) benzoic acids - depending on the reaction conditions. The isocoumarins are synthesized in good yields whereas the carbazole synthesis suffers from lower yields and contamination with the corresponding simultaneously formed isocoumarin product. Mostly symmetrical acetylenes were studied with the exception of one example (R⁵ = Me, R⁶ = Ph) leading to a clean isocoumarin product A, but the corresponding carbazole B was contaminated with other isomers and the yield was low. The substituent effect on the benzoic acid fragment could have been more widely studied.