Oxazole, dihydro

Oxazole, 2,5-dihydro-4-methoxy-synthesis, 6, 228 Oxazole, dihydro-2-methylene-reactions, 6, 215... 

Similar alkylations may be effected on oxygen. l-(2-Chloroethyl)imidazolidin-2-one (312) when treated with potassium hydroxide or sodium hydride underwent ring closure to the tetrahydroimidazo[2,l-6]oxazole (313) (57JA5276). This approach can be used for the preparation of bicyclic hydantoins and the corresponding dihydro derivatives of (313) using the mesylate of (312) and NaH (77JHC5U, 79JMC1030). 

Thieno[3,4-d]oxazole-3a(4H)-carboxylic acid, dihydro-2-methyl-synthesis, 6, 1020 Thieno[2,3-d Joxazoles synthesis, 6, 990 Thieno[3,2-g]pteridine structure, 3, 284 lH-Thieno[3,4-c]pyran-2-ones synthesis, 4, 1032 Thienopyrazines synthesis, 4, 1022-1024 Thieno[2,3-6]pyrazines, 4, 1023 electrophilic substitution, 4, 1024 Thieno[3,4-6]pyrazines, 4, 1024 Thieno[3,4-c]pyrazole, 4,6-dihydro-3-hydroxy-carbamates... 

The gold complex, generated in situ from bis(4-isocyanocyclohexyl)gold(I) tetrafluoroborate and (A)-A-methyl-,V-[2-(dialkylamino)ethyl]-l-[(5)-r,2-bis(diphenylphosphino)ferrocenyl]eth-ylamine, is an effective catalyst for the aldol reaction of various aldehydes with methyl iso-cyanoacetate to give the trans- and cw-4,5-dihydro-l,3-oxazoles. Depending on the aldehyde, the transjeis product ratio ranges from 84 16 to 100 0, and the ee of the main diastereomer is between 72 and 97%26. 

Under inversion of the configuration at sulfur, enantiomerically pure 4,5-dihydro-2-[(7 )-sulfinylmethyl)]oxazoles (e.g 2) are obtained from metalaled 4,5-dihydrooxazoles and (-)-menthyl (5,)-4-methylbenzenesulfinate31. 

Metalation of 4,5-dihydro-2-[(7 )-sulfinylmethyl]oxazoles (e.g., 2) with butyllithium at -90 C and reaction of the chiral azaenolates with aldehydes furnishes the hydroxyalkylated sulfinylox-azole derivatives 3 which are desulfurized to give the 4,5-dihydro-2-(2-hydroxyalkyl)oxazoles 4. The corresponding 3-hydroxy acids 5 are obtained by acidic hydrolysis in 60-85% overall yield and 26-53% ee31. 

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-... 

Methyl-2-phenyl-4-athoxycarbonyl-l,5-dihydro-l,3-oxazol wird je nach Menge Li-thiumalanat entweder selektiv zum Alkohol reduziert oder man erhalt unter Ringspaltung 2-Benzylamino-3-hydroxy-butandiol-(1,3) (s. S. 347). 

Phenylacetylamino-2-methyl-propanol5 Zu einer Losung von 0,5 g (2,46 mMol) 5-Oxo-4,4-dimethyl-2-benzyl-4,5-dihydro-1,3-oxazol in einem Gemisch von 15 ml THF, Athanol und Wasser (1 1 1) werden unter Riihren in kleinen Portionen 0,05 g (1,3 mMol) Natriumboranat gegeben. Man laBt 20 Stdn. bei 20° stehen, siiuert an, cngt ein, extrahiert mit Diathylather, trocknet, entfernt die Solventien i.Vak. und kristallisiert den Riickstand aus Diathylather Ausbeute 0,47 g (91% d.Th.) F 75-76°. 

Analog erhalt man aus 5-Oxo-2-phenyl-4,5-dihydro-1,3-oxazol 2-Benzoylamino-athanol5 (88% d.Th.) und mit Lithiumalanat aus 5-Oxo-4-methyl-2-benzyliden-2,5-dihydro-1,3-oxazol 2-Phenylacetylamino-propanol (30% d.Th.)6. Calciumboranat reduziert 5-Oxo-2-phenyl-4-benzyliden-4,5-dihydro-1,3-oxazol zu oc-Benzoylamino-zimtal-kohol1. 

Diphenyl-4,5-dihydro-l,2-oxazol —> cis-3-Phcnyl-2-benzyl-aziridin 31% d.Th. 

Cyclische 0,N-Acetale vom Typ der 1,3-Oxazolidine und 2,5-Dihydro-l,3-oxazole werden durch Lithiumalanat7 und Natriumboranat8,9 zu 2-Amino-alkoholen reduziert. Aus 3-Methyl-2-phenyl-l,3-oxazolidin wird z.B. mit Natriumboranat 2-(N-Methyl-N-benzyl-amino)-athanol (74% d.Th) erhalten8 ... 

Symmetrisch substituierte 1,3,4-Oxadiazole liefern dagegen die Tetrahydro-1,3,4-oxadiazole, wahrend 5(2)-Phenyl-2(5)-naphthyl-(2)-l,3-oxazole nur zu 5(2)-Phenyl-2(5)-naphthyl-( 1 )-2,3-dihydro-1,3-oxazolen reduziert werden1 ... 

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]-... 

Methylamino-4,5-dihydro-(3,4l6-tri-0-acetyl-1l2-dideoxy-a-D-glucopyranoso)[2,1 -cfl-1,3-oxazole... 

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