Oxazolo quinoline-4-ones

H,4H-Oxazolo[5,4,3-y]pyrido[3,2-g]quinolin-4-one, 8-hydroxymethyl-6-methyl — see Nybomyein 5H-Oxazolo[2,3-[Pg.731]

The most efficient routes to the cationic oxazolo[3,2- ]pyridine ring system 351 rely on the method of Bradsher and Zinn <1967JHC66> involving the cyclocondensation of iV-phenacyl-2-pyridones 349 obtained by alkylation of readily available 2-pyridones 347 (Scheme 95). This method has been used by Babaev et al. to prepare a series of 6-nitro-oxazolo[3,2- ]pyridines 355 from 5-nitro-2-pyridone 352 in excellent yields <2003MOL460>. Similarly, tricyclic oxazolo[3,2- ]pyridines 359 have been prepared from the corresponding quinolin-2(177)-ones 356 <2003H(60)131>. 

The isoxazole-to-oxazole rearrangement has been also used in the synthesis of benzocondensed derivatives. The irradiation of benzisoxazoles 81 in water (high-pressure Hg lamp) produces almost quantitative yields of the corresponding ben-zoxazoles 82 (Scheme 12.24) [53]. Benzoxazolin-2-ones 83 are similarly obtained [54], Furthermore, oxazolo[5,4-b]pyridines 84 and oxazolo[5,4-b]quinoline 85 are obtained by preparative-scale photolysis in ether with a high-pressure Hg lamp of the corresponding isoxazolo[5,4-b]pyridines or isoxazolo[5,4-b]quinoline, respectively (Scheme 12.24) [55]. 

Oxazolo[4,5-/2]quinolin-2(3//)-ones could be acylated effectively at the N-3 position with reagents such as AcCl, ethyl chloroformate, trans-cinna.moy chloride, and dimethyl carbamoyl chloride... 

The oxazolo[4,5-/z]quinolin-2(3//)-ones (89) and 2,5-disubstituted oxazolo[4,5-/i]quinolines (90) were prepared as new antiallergic agents by oxazole ring annelation conducted by condensing 7-amino-8-hydroxyquinoline intermediates with phosgene, o-ester, or imidate reagents (Scheme 7)... 

The methylene bridge in the fused oxazoline (203), 6-methyl-2//,6//-oxazolo[5,4,3-j/]quinolin-4-one, shows great stability towards acid cleavage, such as heating in 47% hydriodic acid. It is cleaved by oxidation, however, when treated with activated manganese dioxide in acetic acid (73JA5003). 

If the Reissert compound from the reaction with ethyl chloroformate (224) is lithiated at C-2 and subsequently treated with benzaldehyde, the final product is the l//-oxazolo[3,4-a]quinolin-l-one (225) (73JHC99). 

The most efficient route to the cationic oxazolo[3,2- ]pyridine ring system 69 relies on the cyclocondensation of N-phenacyl-2-pyridones 68 obtained by alkylation of 2-pyridones 67 (Scheme 41) <1967JHC66, CHEC-III(11.10.7.8) 479>. The use of this method is exemplified by the preparation of tricyclic oxazolo[3,2- ]pyridines 71 from the corresponding quinolin-2(l//)-ones 70 (Scheme 42) <2003H131>. 

Substituted oxazolo[4,5-Z ]pyridines 138 (and quinolines) were synthesised in high yields from zwitterion or hydroxyamidine derivatives 137, obtained by treatment of non-enolisable amides 136 with the complex base NaNH2-/-BuONa, via hetaryne intermediates. Intramolecular cyclization and NH3 elimination to give 138 were performed in dimethylacetamide by heating or microwave irradiation <03S2033>. Different approaches to oxazolo[4,5-c]quinoline-4(5/f)-ones from ethyl 2-chlorooxazole-4-carboxylate have also been described <03OL2911>. 

An efficient, diverse synthesis of oxazolo[4,5-c]quinoline-4-ones and thiazolo[4,5-c]quinolines-4-ones is carried out in two steps from readily available starting materials <03OL2911>. The Suzuki-Miyaura coupling reaction was employed. 

Oxazolo[3,2-a pyrimidin-4-ium, 807 Oxazolo 5,4-d]pyrimidin-7-one, 714 Oxazolo[4,5-b]quinolin-2-one, 1226... 

Other heterocyclic systems prepared from these oxazolones include oxazolo[ 5,4-61 quinolines,44 pyran-2-ones,45 pseudoxazolones,46 and indole derivatives.47... 

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