Knoevenagel Reactions of 6,7-Dihydropyrrolo[2,3-c]azepine-4,8(1H,5H)-dione: An Approach to the Synthesis of Pyrrolic Marine Natural Products

The title compound undergoes reaction with diethyl malonate or ethyl hydrogen malonate in the presence of TiCl4 to give a mixture of endocyclic and exocyclic products, (5) and (6) or (13) and (14). The latter compounds have been decarboxylated and brominated to give the allylic bromide (18). Model experiments to substitute the bromine with amines suggest this compound would prove to be only a mediocre intermediate for the synthesis of the pyrrolic guanidine (2) found in Phakellia flabellata .