On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines

Abstract

2,3-Diaminophenol 4, 3,4-diaminophenol 5, 4-methoxy-1,2-diaminobenzene 6, 3,4-diaminobenzenethiol 7, 2,3-diaminobenzoic acid 8, and 3,4-diaminobenzoic acid 9 were reacted with 2,4-pentanedione to yield the corresponding benzo[b][1,4]diazepinium salts, respectively. The hydroxy-benzo[b][1,4]diazepinium salts 17 and 18 do not form mesomeric betaines (MB) on deprotonation. Instead, they are converted into the diimines 24 and 25. By contrast, the 7-mercaptobenzo[b][1,4]diazepinium salt 20 yields the corresponding thiolate on increasing the pH of the solution. This MB, which possesses 4n pi-electrons, does not fit into the classification system of heterocyclic mesomeric betaines accepted today. Deprotonation of the betaine results in the formation of an instable anionic thiolate 31 which oxidizes immediately to the disulfide 32. The carboxy derivatives 21 and 22 readily form cross-conjugated mesomeric betaines. Whereas the diimine 34 proved to be instable, the sodium salt of the diimine 36 was unambiguously characterized. An X-ray single crystal analysis of 22 as its picrate is presented in order to gain additional insights into these 4n pi-electron systems.

Direct Photochemical C–H Carboxylation of Aromatic Diamines with CO2 under Electron-Donor- and Base-free Conditions

“…3b and Supplementary Fig. 5 , Supplementary Tables 2 and 3 ) 57 , 58 . Interestingly, one ortho C–H bond relative to an amino group was carboxylated.…”

Pyrimidine‐Annulated Pyrrolobenzodiazepines. A New Ring System Related to Aspergillus Alkaloids

“…This configuration has been identified as important to the pharmacophore of these compounds. The biological activity of anthramycin, tomaymycin, chicamycin, neothramycin, and other PBDs from Streptomyces species is due inter alia to their ability to form aminal bonds In continuation of our interest in alkaloids, [24,25,26,27] nucleobase betaines, [28,29] and ionic heteroaromatics, [30,31,32] we became interested in this class of compounds because some alkaloids, circumdatin A-G, had been isolated from the fungus Aspergillus ochraceus and proposed as suitable chemotaxonomic markers for this species. [33] Total syntheses of circumdatin C and F, [34] and a building block approach to a diverse multi-arrayed library of the circumdatin family by means of aza-Wittig reactions [35] were published recently, demonstrating the interest in derivatives of this ring system.…”

Metathesis‐Based De Novo Synthesis of Noviose

“…In continuation of previous studies from our group on the metathesis-based synthesis of deoxy sugars and their derivatives, [28][29][30][31][32][33][34] in this paper, we report a synthesis of l-(+)-noviose using S-ethyl lactate as a conveniently available enantiomerically pure starting material. To the best of our knowledge, lactic acid or its derivatives have not been used as enantiopure starting materials for the synthesis of noviose or its derivatives before.…”

“…We have previously made similar observations for other metathesis reactions. [52] A successful methylation of the C-4 hydroxy group was eventually accomplished by replacing the strongly basic reagent NaH by silver oxide. This method has previously been used for the alkylation of base-sensitive substrates [29,53,54] or sterically encumbered alcohols.…”