Synthesen mit Alkendiazoniumsalzen, V. Synthese und Struktur von 1,3,4‐Oxadiazolen, 6H‐1,3,4‐Oxadiazinen und 5,6‐Dihydro‐4H‐1,3,4‐oxadiazinen

Abstract

Die Umsetzung von Alkendiazoniumsalzen 1 rnit Carbonsaurehydraziden 2 fuhrt in Abhangigkeit von den Substituenten R' und R2 zu 1,3,4-0xadiazolen 6,6H-1,3,4-Oxadiazinen 7 bzw. zu 5,6-Dihydro-4H-1,3,4-oxadiazinen 8. Zur Sicherung der Konstitution von 6b, 7 Be und 8b wurden Rontgenstrukturanalysen durchgefuhrt. Syntheses with Alkenediazonium Salts, V ' )Synthesis and Structure of 1,3,4-Oxadiazoles, 6H-1,3,4-0xadiazines, and 5,6-Dihydro-4H-l,3,4-oxadiazines Depending on the substituents R' and RZ the reaction of alkcncdiazonium salts 1 with carboxylic hydrazides 2 leads to 1,3,4-0xadiazoles 6,6H-1,3,4-oxadiazines 7, and 5,6-dihydro-4H-1,3,4-oxadiazines 8, respectively. The structures of 6b, 7Be, and 8b were established by X-ray analysis.Ein eingehendes Studium der Umsetzung der von Bott eingefuhrten Vinyl-diazoniumsalze2) rnit primaren Aminen ergab, daI3 diese Reaktion eine neue, besonders einfache Variante zur Herstellung von l-Alkyl-1H-l,2,3-triazolen'~3~ darstellt, die eine nahezu freie Wahl der Aminkomponente erlaubt. Ausschlaggebend fur die Bildung der 1 H-l,2,3-Triazole ist wahrscheinlich der Primarangriff der Amine auf die Vinyldiazoniumsalze, wobei unter 0-C-Kupplung intermediar zunachst 2-Amino-diazoalkane entstehen1a3). Die dabei freiwerdende Saure wird durch uberschussiges Amin abgefangen.Hydrazine und Hydroxylaminether liefern bei der Umsetzung mit geeignet substituierten Alkendiazoniumsalzen auI3erdem Diazoimine').In einigen Fallen konkurrieren die aus Alkendiazoniumsalz und Aminkomponente (aromatische Amine, Hydroxylaminether) entstehenden Diazoverbindungen als Base mit dem Amin um die freigesetzte Saure, und man erhalt Alkyldiazonium-Zwischenstufen, deren Zersetzung unter anderem zu Imidoestern fiihrt').

A computational study (DFT, MP2, and GIAO‐DFT) of substituent effects on protonation regioselectivity in β,β‐disubstituted vinyldiazonium cations: formation of highly delocalized carbenium/diazonium dications

“…Stability of alkenediazonium ions toward dediazoniation varies greatly depending on their structure, ranging from those that can be isolated as salts and stored indefinitely at room temperature,10–17 to those that require in situ generation and trapping,18–20 to those that can be generated at low temperature under stable ion conditions for direct NMR studies 21, 22. In this way, generation of alkenediazonium salts has been accomplished, either as reactive intermediates or as isolable compounds, by diverse synthetic routes 10–17. Stable ethenediazonium salts were generally synthesized by O ‐alkylation of alkyl diazoacetates or α ‐diazoacetamides with Meerwein salts, diazotization of vinyl isocyanates, or ionization of tosyl hydrazones 10–17.…”

“…In this way, generation of alkenediazonium salts has been accomplished, either as reactive intermediates or as isolable compounds, by diverse synthetic routes 10–17. Stable ethenediazonium salts were generally synthesized by O ‐alkylation of alkyl diazoacetates or α ‐diazoacetamides with Meerwein salts, diazotization of vinyl isocyanates, or ionization of tosyl hydrazones 10–17. For example, O ‐ethylation of ethyldiazoacetate generated stable 2,2‐diethoxyethenyldiazonium salts 16.…”

“…Early progress on solvolytic generation of vinyl cations by deamination of suitable substituted vinyl amines, via the in situ generated vinyldiazonium ions, has been reviewed 23. Introduction of electron‐releasing substituents in the β ‐position or incorporation of vinylic bond into an appropriate ring system tends to suppress this fragmentation reaction 10–17…”