An analysis of the n.m.r. spectra (1H, 13C, and, in part 15N and 17O) of pyrrolizin-3-one, and of its aza-derivatives pyrrolo[1,2-c]imidazol-5-one, pyrrolo[1,2-a]imidazol-5-one and pyrrolo[1,2-b]pyrazol-6-one

Abstract

The ¹H and ¹³C n.m.r. parameters (chemical shifts and coupling constants) of the title compounds (1)–(4) are assigned unambiguously, and are compared with those of monocyclic model compounds. The picture of the conjugation which emerges—and which is in general supported by ¹⁵N and ¹⁷O n.m.r. studies of (1)–is indicative of some amide- like interaction between the ring-junction nitrogen atom and the carbonyl group, but there is no evidence for cyclic delocalisation of the resulting 8π-electron system.