Benzo oxazoles

Oxo-2,3-dihydro-(benzo-l,3-oxazole) werden durch Lithiumalanat zu den entsprechenden 2-Methylamino-phenolen aufgespalten. Aus 2-Oxo-2,3-dihydro-(benzo-1,3-oxazol) selbst erhalt man2-Methylamino-phenolzu 57% d.Th.11. 2-Oxo-3-chlorme-... 

Nitro-bcnzaldehyd wird unter RingschluB zu Benzo-[c]-l,2-oxazol reduziert (Bd. X/l, S. 878). 

Nitro-benzophenon wird an Blei (geteilte Zelle, Athanol/Wasser/Natriumacetat) zu 3-Phenyl-(benzo-[c]-l,2-oxazol) (86% d.Th.) cyclisiert4 ... 

Auf ahnliche Weise erhalt man aus 2-Nitro-benzaldehyd in waBrig-alkoholischer Ace-tatpuffer-Losung Benzo-[c]-l,2-oxazol (51% d.Th.)1 ... 

Durch Spaltung der Seitenkette kann 2-Hydroxylamino-benzaldehyd entstehen, der an-schlieBend zum Benzo-[d]-l,2-oxazol cyclisiert (s.S. 691). 

Bis-[ ( benzo-1,3-oxazol) -yl-(2)-thio]- 343 Bis-[1,4- (bzw. 3,4]-dihydro-naphthy[-(2)-oxy]- 588 Bis-[dimethylamino]- 345 Bis-[4-dimethyIamino-phenyl]- 346 Bis-[4-hydroxy-phenyl]-(2-carboxy-phenyl)- 167 Bis-[4-methoxy-phenyl]-dideutero- 346 Bis-[4-methyl-phenyl]-Bis-f 2-methyl-thiiranyl-(2)]- 570 Bis-[naphthyl-(2)-oxy]- 588 Bis-[naphthyl-(2)-thio]-... 

Chiral hydroxy benzimidazole 267 was dialkylated with dibromomethane or benzaldehyde dimethyl acetal to form benzo[4,5]imidazo[l,2-f]oxazoles 268 and 269 (Equation 118) C1997TA1491, 1998TA2245>. After removal of the BOC group and formylation of the liberated amine, formylaminomethylthiazole cyclized in phosphoryl chloride to... 

A new heterocyclic system, 3 ,4-dihydro-3//-benzo[4,5]imidazo[l,2-f]oxazol-l-one 462, was synthesized by reaction of 4,4-dimethyl-5-methylene-l,3-dioxolan-2-one with o-phenylenediamine in the presence of copper bromide as catalyst in carbone dioxide at 60-80 °C under high pressure (Equation 217) <1999CHC216>. 

Sulfur. Thiophene and benzo[ >] thiophene are both aromatic heterocycles, as discussed earlier in this review. Isothiazole is a planar molecule with an aromaticity comparable with those of thiazole and pyrazole, and higher than those of isoxazole and oxazole,122 140 as evaluated on the basis of Bird s aromaticity index A, based upon the statistical degree of uniformity of the bond orders of the ring periphery. Theoretical calculations and experimental data in connection with the aromaticity of isothiazole have been reviewed.141 Thiazole is also viewed as an aromatic molecule, similar to thiophene. It lacks an experimental aromaticity value, but the heat of formation together with bond lengths and angles have been calculated by various computational meth-... 

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

Rather, the intent of the current project is to provide the reader with a discussion and leading examples of significant advances made in the synthesis, reactions, and applications of mononuclear oxazoles, oxazolones, oxazolines, and chiral bis(oxazolines) during this time frame. The material focuses on the more recent literature, although an update of the older synthetic literature is included wherever possible. In an effort to be selective, references to relevant reviews of material, not discussed in a chapter, are provided. Completely reduced oxazoles, that is, oxazolidines as well as benzo-fused derivatives, are outside the scope of this review. 

Fio. 1. Bronsted plot for azoles reacting with methylating agents in quaternization reactions. Pyridine is the reference substrate. 1, 1-methylimidazole 2, 1-methylbenzimidazole 3, thiazole 4, 1-methylpyrazole 5, 2-methylindazole 6, benzo-thiazole 7, oxazole 8, 1-methylindazole 9, benzoxazole 10, 2,1-benzisothiazole 11, isothiazole 12, 2,1-benzisoxazole 13, isoxazole and 14, 1,2-benzisoxazole. 

Introduction Pyrroles Indoles Pyridines Thiophenes and Benzo[b]thiophenes Furans and Benzo[b]furans Thiazoles and Benzothiazoles Oxazoles and Benzoxazoles Imidazoles Pyrazines and Quinoxalines Pyrimidines... 

Heptenoic Acid 2-Benzo> amino-2-trilluoromethyl- EI0b2. 211 f. (4.5-H-,— 1,.3-oxazol-Der. + H20)... 

Treatment of 2- or 4-(p-formylphenyl)-2/f-l,2,3-triazoles with p-tolyl-substituted heterocycles such as benzo[6]furans,58,63 benzol-thiophenes,56,63 benzoxazoles,63,64 benzisoxazoles,54 oxazoles,63 isoxa-zoles,63 oxadiazoles,63,65 benzotriazoles,63 and y-triazolo [ 1,5-a]-pyri-dines19 has led to the formation of a number of new stilbene derivatives some of which are shown in Table XI. 

N1 - BENZO 6,7)-1,4-DIAZEPINO-(5,4-b)-OXAZOL-6-ONE, lO-CHLORO-2,3,5,6,7,11b- HEXAHYDRO-2-NETHYL-llb-PHENYL-... 

Nishio et al. <2002HCA2383> performed a photochemical [2+2] cyclization reaction between jV-a 1 koxycarbony 1 -benzo-l,3-oxazol-2-thione 108 and a noncyclic alkene 109. The reaction led to the formation of spiro-thietanes 110, in most cases in high yields (Table 8). They also reported <2003HCA3255> that when in a similar reaction a cycloalkene was used, the reaction led to the formation of compounds 111 and iminothietanes 112. Cyclopentene and indene were used as model cycloalkenes (Scheme 17). 

Crozet, Vanelle and coworkers94 have also described the first example of an S l reaction involving an oxazole system activated by a non-fused tetrasubstituted p-benzo-quinone 17, with 2-nitropropane anion (equation 26). 

In accord with MO calculations (67BCJ1580), benzo[Z>]furans are attacked by a variety of nucleophiles at the 2-position. Hydroxide under drastic conditions affords (59) and (60), which are presumably formed by Cannizzaro reaction of the aldehyde (58 Scheme 31). Methylsulfinyl anion in DMSO at 70 °C followed by aqueous work up affords 2-ethy-nylphenol (66JOC248). With a -M group at the 3-position, nucleophilic attack at the 2-position is facilitated. 3 -Benzoyl-2-ethylbenzo[Z> ]furan with hydroxide affords products which can be rationalized by / - diketonic fission of the intermediate (61), further transformations of which produce (62) and (63) (Scheme 32). With a nitrile at the 3-position a similar degradation takes place but an ester is not sufficiently electron withdrawing and hydrolysis ensues. Ammonia will attack the ketone (64) at the 2-position, producing the unstable / - enaminoketone (65 Scheme 33). Other nucleophiles attack in a similar manner thus hydroxylamine under certain conditions will afford oxazoles (66BSF1587). 

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