1.3- Oxazole-2,4-diones

H,3H- Pyrrolo[l, 2-c]oxazole-l, 3-dione, 5,6,7,8-tetrahydro-IR spectra, 6, 978 [2.2](2,5)Pyrrolophane, N-aryl-rearrangements, 4, 209 Pyrrolophanes natural products, 7, 764 synthesis, 7, 771 Pyrrolophanes, N-aryl-synthesis, 7, 774 (2,4)Pyrrolophanes synthesis, 7, 771 Pyrrolo[3,4-c]pyran-4-ones synthesis, 4, 288 Pyrrolopyrans synthesis, 4, 525, 526 Pyrrolopyrazines synthesis, 4, 526 Pyrrolo[l, 2-a]pyrazines synthesis, 4, 516 Pyrrolo[2,3-6]pyrazines Mannich reaction, 4, 504 Vilsmeier reaction, 4, 505 Pyrrolo[3,4-c]pyrazole, 1,3a,6,6a-tetrahydro-structure, 6, 976 synthesis, 6, 1019 Pyrrolopyrazoles synthesis, 5, 164 Pyrrolo[l,2-6]pyrazoles synthesis, 6, 1002, 1006 Pyrrolo[3,4-c]pyrazoles reactions, 6, 1034 synthesis, 6, 989, 1043 Pyrrolo[3,4-c]pyrazolones synthesis, 6, 989 Pyrfolopyridazines synthesis, 4, 517 Pyrrolo[l, 2-6]pyridazines synthesis, 4, 297 6/7-Pyrrolo[2,3-d]pyridazines synthesis, 4, 291 2/f-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291 6/7-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291... 

Chemical Name 21 -(Acetyloxv)-9-fluoro-11 -hvdroxv-2 -methyl-5 H-pregna-1,4-dieno-[17,16-d] oxazole-3 0-dione... 

CN (lip,16(i)-21-(acetyloxy)-9-fluoro-ll-hydroxy-2 -methyl-5 H-pregna-l,4-dieno[17,16-d]oxazole-3,20-dione... 

C22H2XO3 14135-32-1) see Betamethasone 17a-hydroxy-16P-methyl-5p-pregn-9(ll)-ene-3,20-dione (C22H32O3 13656-78-5) see Betamethasone 21-hydroxy-2 -methyl-5p//-5a-pregn-9(ll)-eno[17,16-d]-oxazole-3,20-dione acetate (ester)... 

Methyl-2-phenyl-oxazol-4-yl)ethoxy]benzo[2]thiophen-7-yl]methyl]-thiazolidine-2,4-dione. 

Frequently, five-membered heterocyclic systems have provided the C(3)N(4)C(5)C(6) fragment in 1,2,4-triazine syntheses. For instance, the oxazol-5-one (586) reacts with hydrazines to give, via open-chain intermediates (587), the l,2,4-triazine-3,6-diones (588)... 

Furoic acids — see Furancarboxylic acids Furo[3,4-d]isothiazole-4,6-dione, dihydrosynthesis, 6, 999 Furo[2,3-d]isoxazoles synthesis, 5, 148 Furo[3,2-d]isoxazoles synthesis, 6, 997 Furo[3,4-d ]is oxazoles... 

Intramolecular cyclization of 4,5-dihydro-3-(2-thienyl)-oxazol-2-ones 39 gave 1 -hydroxyethylthieno[2,3-d]pyrimidine-2,4(3// )-diones 40... 

Azole approach. 2-Aminooxazoles react with arylisocyanates on heating to form 2H-oxazolo[3,2-a][l,3,5]triazine-2,4(3//)-diones (220). The bicyclic system can also be formed by treatment of the oxazole acetamide or the oxazole urea with two moles of an isocyanate under the same reaction conditions (71JMC1075). 

Numerous applications of IR spectral data have been reported for derivatives of (5,5)-fused ring systems, especially in connection with the problem of tautomeric equilibria. For example, the IR spectra of 5,6,7,8-tetrahydro-l//,3H-pyrrolo[l,2-c][l,3]oxazole-1,3-diones (24 X=0) and corresponding thiazole-l,3-diones (24 X = S) show no carbonyl absorption, but broad bands at 3300 cm-1 due to the associated OH group, indicating that the fused structures (24) exist in the enolic forms rather than their diketonic tautomers (81BJC1844). 

Various other [3 + 2] cycloadditions, affording chiral, anellated C6o derivatives with stereogenic centers in the addends are reported in literature. The products were generally obtained as racemates and resulted from reaction of buckminsterfullerene with species like 2,3-disubstituted 2//-azirincs (via nitrile ylides [under direct irradiation] or via 2-azaallenyl radical cations [sensitization by photoinduced electron transfer]),365 1-substituted 5-diazopentane-1,4-diones (via cyclic carbonyl ylides),366 7-alkylidene-2,3-diazabicyclo[2.2.1] hept-2-ene (via a diradicaloid trimethylenemethane derivative),367 1-benzylpy-razolidine-3-ones in the presence of aldehydes (via pyrazolidinium ylides),368 2-trifluoromethyl-2,5-dihydro-l,3-oxazol-5-ones (via nitrile ylides),369 nitro-alkanes in the presence of triethylamine and trimethylsilyl chloride (via N-silyloxynitrones),370 or dv-HOCH2 CH=C H C H 2 OCO 2 H( in the presence of... 

S)-Tetrahydro-l -methyl-3,3-diphenyl-1 H,3H-pyrrolo[l, 2-e][1,3,2]oxazaborole-boran complex Boron, trihydro(tetrahydro-1 -methyl-3,3-diphenyl-1H,3H-pyrrolo[1,2-c][1,3,2]oxazaborole-N7)-, [l-4-(3aS-cis)]- (12) (112022-90-9) (S)-Proline-N-carboxyanhydride lH,3H-Pyrrolo[1,2-c]oxazole-1,3-dione, tetrahydro-, (S)- (9) (45736-33-2)... 

Allenes may take the place of alkenes in this process, leading to ero-methylenesuccinimides as products. With unsymmetrically substituted allenes, the less-substituted double bond is chemoselectively in-coiporated into the heterocyclic ring. The alkene may also be replaced by an aldehyde in this cycloaddition, leading to l,3-oxazole-2,4-diones (Scheme 20). ... 

Scheme 10 Potential Cyclization Reactions in the N-to-C Peptide Synthesis in Solution and on Solid Supports Oxazol-5(4/()-one (Path a) and Piperazine-2,5-dione Formation (Path b)...

Only a few oxazoloquinones are known. 2-Methylnaphtho[2,3-d]oxazole-4,9-dione (207) was obtained from 2-acylamino-3-alkylamino-l,4-naphtho-quinone in the presence of concentrated sulfuric acid (69T2427). Similarly, derivatives of 208 were obtained from 2,5-bis(acetylamino)-3,6-dihydroxy-1,4-benzoquinones and acyl halide or anhydride (64ZOB3037). The five-membered ring is easily cleaved in warm dilute acid or base (64ZOB3037). 

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