Tautomerism, regioisomerism, and cyclization reactions of acridinyl thiosemicarbazides

✍ Scribed by Karel D. Klika; Eva Balentová; Kalevi Pihlaja; Juraj Bernát; Ján Imrich; Martina Vavrušová; Erich Kleinpeter; Andreas Koch

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2006
• Tongue: English
• Weight: 954 KB
• Volume: 43
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570430317

✦ Synopsis

Abstract

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The regioselectivities of methyl‐ and phenylhydrazine with acridin‐9‐yl isothiocyanate (thus yielding thiosemicarbazides with acridine substituted on the urea‐type side) were examined. Methylhydrazine regioselectivity was high with the α‐nitrogen atom overwhelmingly more nucleophilic than the β‐nitrogen atom; phenylhydrazine regioselectivity was poor but varied with the solvent and only in the case of ethanol was nucleophilic predominance of the α‐nitrogen atom pronounced. Of note, whilst both phenyl thiosemicarbazides were present in solution only as spiro forms, the methyl product was present as an equilibrium mixture of open‐chain and spiro thiosemicarbazides. Reactions on the NH~2~ blocked analogue of methyl acridin‐9‐ylthiosemicarbazide (1‐isopropylidene‐2‐methylthiosemicarbazide) were also examined. Interestingly, present in the starting material itself was a structural motif of novelty wherein a triazolethione represented the major species of an equilibrium between cyclic and open‐chain forms.