1.2.5- Oxadiazolo pyridines

Reaction of 3,5-dinitro-4-hydroxyaminopyridine with picryl chloride in the presence of base affords the oxadiazolo-pyridine 22 and picric acid (Equation 14) <2000CHE1003>. 

Oxadiazolo[3,4-c]pyridine, 3(l)-oxo-synthesis from 4-azido-3-nitropyridines, 6, 730... 

Bfx PPhj Bfz Described for the synthesis of l,2,5-oxadiazolo[3,4-c]pyridine system [3]... 

Acylation of the piperazine nitrogen atoms of 47/,87/-bis[l,2,5]oxadiazolo[3,4- 4 -< ]pyrazine 59 with acetyl bromide proceeds smoothly in the presence of pyridine in acetonitrile to give 60 (Equation 9) <1997CHE618>. 

Hydroxy-7-phenylindeno[l,2-A]-l,2,5-oxadiazolo[3,4- /]pyridine can have four polymorphic forms in the solid state, of which two are yellow and two are red. Two of them are interconvertible (yellow/red) upon exposure to different solvents. X-ray crystal structure analysis of one of the red forms shows the phenyl ring and the indenoox-adiazolopyridine ring to be coplanar <1999H(50)895>. 

DIOXAZOLONES, FURAZAN N-OXIDES HYDROXYLAMINIUM SALTS, ISOXAZOLES, 2H-1,2,4-OXADIAZOLO[2,3-a]PYRIDINE-2-TfflONES OXIMES, OXIME CARBAMATES... 

In l,3,4-oxadiazolo[3,2-a]pyridinium salts (15) an 0/As exchange can be achieved with tris(tri-methylsilyl)arsine in boiling acetonitrile to yield l,2,4-diazaarsolo[l,5-a]pyridines (16) (R = Me, Pr, Bu, Ph) (Equation (4)) <87TLl5li>. In a corresponding way the compound (17) with R = O-TMS is obtained. Methanolysis gives the hydroxy derivative (18) which exists exclusively in this tautomeric form and which can be O-acylated via the sodium salt (Scheme 3) <88TL3387>. 

NMR spectroscopy <2000JP0480>. The X-ray crystallographic data of a series of electron donors containing 1,2,5-thiadiazole and l,l -dihydro-4,4 -bi(pyridylidene) units have been reported <1997CC1851>. The fluoresence spectroscopic characterization of 4,7-bis(2-thienyl)-l,2,5-oxadiazolo[3,4-f]pyridine 2 has also been reported <2002CPL(354)173>. 

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