An anomalous reaction of a 4-chlorocoumarin dimer with amines: the formation of benzopyranocoumarin derivatives from the dimer

Reaction of an anti head-to-tail 4-chlorocoumarin dimer with amines afforde d benzopyranocoumarin derivatives in high yields; the reaction is quite dif ferent from the expected reaction of coumarin dimer derivatives with amines . On the basis of spectral information, a possible reaction mechanism is pr oposed through a tandem lactone ring-opening reaction, elimination, cyclore version of cyclobutene, addition-elimination, and Michael addition. (C) 199 9 Elsevier Science Ltd, All rights reserved.