Synthesis and properties of 5,6-dihydrodipyrrolo[1,2-d;2′,1′-g][1,4]diazepin-11-one

Abstract

Treatment of 1,2-di(pyrrol-1-yl)ethane 4 with oxalyl chloride gave a low yield of 5,6-dihydrodipyrrolo[1,2-d;2′,1′-g][1,4]diazepin-11-one 2, by an unexpected electrophilic substitution–decarbonylation process. The diazepinone 2 is unreactive to electrophiles, but can be deoxygenated to 5,6-dihydro-11H-dipyrrolo[1,2-d;2′,1′-g][1,4]diazepine 9 with lithium aluminium hydride. Reaction of 1,1-di(pyrrol-1-yl)methane 5 with triphosgene gives the related dipyrrolo[1,2-c;2′,1′-f]pyrimidin-10-one 3. NMR spectroscopic and X-ray crystal structure comparisons of 2 and 3 show that there is unexpectedly greater conjugation in the compound with the core seven-membered ring, 2, even though the molecule as a whole is less planar than 3. The corresponding reactions of 4 or 5 with thiophosgene did not give cyclisation products but the O-methyl thioesters 7 and 8 were obtained (89 and 27%, respectively).