L,3,4-Oxadiazolium-2-olat

The 170 NMR spectrum of 4,5-diphenyl-l,3,4-oxadiazolium-2-olate was reported earlier <1996CHEC-II(4)268>. Since then, no report on 170 NMR spectra of 1,3,4-oxadiazoles has been published. 

Auf diesem Wege konnten aus l-Amino-2-oxo-l,2-dihydro-pyridin mit Phosgen als erste meso-ionische ancllicrte 1,3,4-Oxadiazole die [Pg.536]

Pyridio[2,l-b]-l,3,4-oxadiazolium)-2-olate konnen auch ohne Einsatz von Phosgen synthetisiert werden (vgl. S. 540, 545, 571, 577). 

Bei dieser Reaktion konnen allerdings auch Kohlensaure-bis-hydrazide entstehen. So cyclisiert l-Amino-2-oxo-4,6-diphenyl-l,2-dihydro-pyridin mit Kohlensaure-bis-imidazolid zu 5,7-Di-phenyl-(pyridio[2,l-b]-l,3,4-oxadiazolium )-2-olat innvA 37%iger AusbeutelS0(vgl. S. 533, 535). AuBerdem wird 1,3-Bis-[4,6-diphenyl-2-oxo-l, 2-dihydro-pyrido -harnstoff (45%) gebildet. 

UV spectra of 1,3,4-oxadiazoles have been described (66AHC(7)183) and the spectra of isosydnones (l,3,4-oxadiazolium-2-olates) have been recorded (69JCS(B)ll85>. 

Meso-ionic 1,3,4-Thiadiazoles.—The synthesis and properties of isomeric pairs of l,3,4-thiadiazolium-2-olates (128) and of l,3,4-oxadiazolium-2-thiolates (127) have been described, thus establishing the existence of isomeric meso-ionic compounds, the interconversion of which [(127) (128)] involves an exchange... 

Chloro(hydroxyimino)methyl]-3-phenyl-l,2,3-oxadiazolium-5-olate-(3-phenylsydnone-4-carbohydroximoyl chloride) reacts in situ (through nitrile oxide) with N-arylmaleimides or 2-methyl-N-phenylmaleimide to give 5-aryl-3-(3-phenylsydnon-4-yl)-3a,6a-dihydropyrrolo[3,4-r/]isoxazole-4,6-diones or dame thyl-5-pheny l-3-(3-phenylsydnon-4-yl)-3a,6a-dihydropyrrolo[3,4-d]isoxazole-4,6-diones, respectively (265). 

Oxadiazoles by cyclodehydration. Reaction of the A-nitrosoglycine derivatives (e.g., 562) with acetic anhydride gives l,2,3-oxadiazolium-5-olates (sydnones) (e.g., 563) (Scheme 254). Additional synthetic approaches to 1,2,3-oxadiazoles are discussed in CHEC-III . 

The solvents with the highest dipole moments found to date are zwitterionic 3-alkyl-1,2,3-oxadiazolium-5-olates (sydnones). For example, 4-ethyl-3-(l-propyl)sydnone, a... 

Die Reaktion von 4-Methyl-3-phenyl-l,2,3-oxadiazolium-5-olat mit verschiedenen Alkinen zeigt folgende Reaktivitatsabstufung (120° Xylol)1020,1021 ... 

Aus 4-Methyl-3-phenyl-1,2,3-oxadiazolium-5-olat cntstehen mit Phenyl-ethin und Propinsaure-methyl-ester, aus 4-Phenyl-l,2,3-oxadiazolium-5-olat mit Propinsaure-methylester1022 aus 4-Methyl-l,2,3-oxadi-azolium-5-olat mit Propinsaure-methylester1022 und aus 4-Methyl-l,2,3-oxadiazolium-5-olat mit 1,3-Di-phenyl-3 -oxo-propin1440 I someren-Gemische. 

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