Access to Fluorescent Azines from N‐Heterocyclic Carbene Precursors and N‐Tosylhydrazones

Abstract

An efficient synthesis of azines from the reaction of N‐heterocyclic carbene precursors with N‐tosylhydrazones has been developed. This method avoids the direct use of diazo compounds and allows the synthesis of structurally diverse azines. An azine was further found to exhibit strong yellow fluorescence and shows promise as a reagent for biological imaging.magnified image

A Facile Preparation of N‐Heterocyclic Olefins: Ring‐Opening Polymerization of β‐Butyrolactone and Frustrated Lewis Pair Reactivity**

“…Clean reactions were obtained by reacting 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (Enders’ carbene) with N ‐aziridinylimines 1 a – c in PhH at elevated temperatures (60‐80 °C). Interestingly, these reactions did not result in the formation of NHOs, but instead in the quantitative formation of azines (Scheme S2) [51] . Enders’ carbene thus failed to engage with N ‐aziridinylimines prior to their thermolysis into diazo compounds, which were subsequently trapped by the carbene.…”

“…Interestingly, these reactions did not result in the formation of NHOs, but instead in the quantitative formation of azines (Scheme S2). [51] Enders' carbene thus failed to engage with N-aziridinylimines prior to their thermolysis into diazo compounds, which were subsequently trapped by the carbene.…”

An Update of N-Tosylhydrazones: Versatile Reagents for Metal-Catalyzed and Metal-Free Coupling Reactions

“…The direct functionalization of N-tosylhydrazones is also an efficient strategy for the synthesis of new hydrazones. 124,168,169 In 2017, Wei and co-workers developed a new strategy using aldehyde-derived N-tosylhydrazones and triazolium salts to afford azine products [Scheme 85 (a)]. 168 In this reaction, the triazolium salt acts as a precursor of an N-heterocyclic carbene, which attacks the diazo compound derived from a N-tosylhydrazone via T92 in Scheme 85 (a).…”

“…124,168,169 In 2017, Wei and co-workers developed a new strategy using aldehyde-derived N-tosylhydrazones and triazolium salts to afford azine products [Scheme 85 (a)]. 168 In this reaction, the triazolium salt acts as a precursor of an N-heterocyclic carbene, which attacks the diazo compound derived from a N-tosylhydrazone via T92 in Scheme 85 (a). When the diazo species was attacked by the deprotonated N-tosylhydrazone species T1, followed by loss of nitrogen and elimination via T93, the transformation gave symmetrical azines [Scheme 85 (b)].…”

A facile preparation of N-heterocyclic olefins: ring-opening polymerization of β-butyrolactone and frustrated Lewis pair reactivity

“…Interestingly, these reactions did not result in the formation of NHOs, but instead in the quantitative formation of azines (Scheme S2). 43 Enders' carbene thus failed to engage with Naziridinylimines prior to their thermolysis into diazo compounds, which were subsequently trapped by the carbene. Initial investigations of the ROP of β-butyrolactone (BL) were performed using 2a, 2c, 4a and 4c.…”