Pyrazolo oxazoles

More recently, Jin (92MI2) investigated several mono- and dimethylated cycloheptazol-8-ones. The similarity of the electronic spectra of pyrazolo-tropones 85, 86a, and 87a is explained by the very similar 10-77 systems present. However, the spectra of isoxazoles 90 and 91 and of oxazole 114b are different from those of the pyrazoles. This difference was attributed to the small contribution of the oxygen-atom lone-pair electrons to the conjugation, which minimizes the contribution of the 10-77 system. 

Ahnlich der Reaktion von 3(5)-Amino-lH-pyrazolen mit 3-Oxo-alkansaure-estern verlauft die Umsetzung mit 4-ChLorcarbonyl-3,5-dimethyl-l,2-oxazolen als Dicarbonyl-Aquivalent. Nach Acylierung des 3(5)-Amino-lH-pyrazols und Offnung des 1,2-Oxazol-Rings werden 6-Acetyl-5-hydroxy-7-methyl-[Pg.682]

Brom-6,7-dihydro- -bromid 576 1 H-< Pyrazoliofl, 2-a]py razolium )-3-olat Pyrazolo[5,1-b]-1,3-oxazol... 

Oxazolo[2,3-fe]oxazoles (191 R = CF3, n-C7F,5) have been prepared by acid-catalyzed dehydration of A,A-bis(hydroxyalkyl)amides <82JFC(2l)359>. The imidazo[l,5-6f]imidazole (193) was prepared by reaction of aminoacetonitrile with excess trimethylorthoformate in the presence of catalytic amounts of formic acid <84JOCl2i2>. The reaction is believed to involve the initial formation of the imidate (192) which reacts successively with aminoacetonitrile and the ortho-ester to give the observed product. Pyrazolo[5,l-Z>]oxazoles (198) have been synthesized by reaction of hydrazino alcohols (195) with the Michael adduct (194), prepared from A-isobutylidene-r-butylamine and dimethyl-methoxymethylene malonate <93JHC1529>. The reaction is believed to involve cyclization of the intermediate hydrazones (196) to give pyrazoles (197), which subsequently cyclize to the bicyclic system with loss of dimethyl malonate. 

The oxazolyloxazoline (206) rearranged on heating in toluene to give the imidazo[5,l-Z)]oxazole (207) <75JOC1521>. Treatment of (208) with DMAD at 110°C gave pyrazolo[l,5-Z ]isothiazole derivatives (209) <82ZOR2626>. 

Giori and co-workers prepared pyrazolo[3,4-antitumor agents by photochemical cyclization of the internal zwitterionic diazon-ium salts 581 (Scheme 1.159). 

The fused oxazole derivative 100 was synthesized from 3-azido-3-deoxy-l,2 5,6-di-O-isopropylidene-a-D-allofuranose, the key final step being the reaction of methyl 3-amino-3-deoxy-5,6-0-isopropylidene-p-D-alloside with DMF dimethyl acetal. The annelated pyranoside 101 was obtained by cyclization of a branched chain hexosulose derivative, and the fused triazole-piperidinoses such as 102 were made by a radical cyclization of a 3-pyrazolo-6-iodo-sugar derivative. The spiro-isoxazohne 103 and related isomers have been synthesized by dipolar cycloadditions of mesitonitrile oxide to 2-deoxy-2-C-methyl-ene-pentonic acids, themselves available in five steps from D-mannitol. Intra-... 

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