Azeto[1,2‐a]quinoxaline‐1,3‐diones, a new class of bridgehead nitrogen β‐lactams

Abstract

Two synthetic procedures have been developed for the preparation of azeto[1,2‐a]quinoxaline‐ 1,3‐diones, a novel class of fused heterocyclic β‐lactams possessing a bridgehead nitrogen atom. Both processes are general and afford the title compounds in good yield. The infrared, proton magnetic resonance, and mass spectroscopic properties of the title compounds are discussed.

Carbon and Nitrogen Basicity of Aminothiophenes and Anilines

“…The S−C-1, C-1−C-2, and C-2−C-3 bonds in 3-aminothiophene are longer than in thiophene (Δ r = 0.003−0.005 Å), whereas the C-3−C-4 bond is shorter (Δ r = −0.003 Å) and the C-4−S bond is unchanged. Further information is also provided by 13 C chemical shifts, which are known to be sensitive to the electron density, − and thus provide complementary information to atomic charges. Calculated and experimental shift differences between thiophene and 3-aminothiophene are in very good agreement and point out a large shielding of C-2 (Δδ = −32.4 ppm) as well as a deshielding of C-3 (Δδ = +21.0 ppm), while C-4 and C-5 undergo much smaller changes.…”

“…However, functionally similar species such as aminothiophenes, despite a superficial resemblance, reportedly behave differently from anilines in many respects. In particular, much evidence has been accumulated that 3-aminothiophenes are remarkably more prone to undergo electrophilic substitution at a ring carbon position than at the amino nitrogen. − The basicity and nucleophilicity of 3-aminothiophene, 3,4-diaminothiophene and their N-methylated derivatives were recently investigated by Terrier et al, in comparison with the behavior of the corresponding anilines. , Data obtained through 1 H NMR and potentiometric studies have provided clear evidence that these compounds behave as nitrogen bases in H 2 O-DMSO mixtures, as well as in pure DMSO. The p K values for this acid−base process have been measured and found to compare well with those for structurally related anilines.…”