Cupric bromide mediated oxidation of 4-carboxyoxazolines to the corresponding oxazoles

Structure-Activity Investigations of Analogues of the C15-C26 Phorboxazoles Segment

“…10 The oxidation procedure developed at Bristol-Myers Squibb (Cu(II)/DBU/HMTA in DCM) 11 afforded oxazole esters (-)-15 and (-)-16. The three-step reaction sequence (a,b-unsaturated acids → a,b-unsaturated oxazole ester) proceeded in good overall yield (> 20%).…”

Chemistry of 5-oxodihydroisoxazoles. Part 18.1 Synthesis of oxazoles by the photolysis and pyrolysis of 2-acyl-5-oxo-2,5-dihydroisoxazoles

“…The crude product, collected in both the exit tube and the cold trap, was subjected to radial chromatography (diethyl ether-light petroleum, 1 : 3) affording the title compound (101 mg, 66%) as a colourless oil (Found: M ϩ , 185.0688. C 8 H 11 NO 4 requires M, 185.0688); δ H 1.38 (3 H, t, J 7.13), 2.53 (3 H, s), 4.11 (3 H, s) and 4.38 (2 H, q, J 7.13); δ C 11.7, 14.2, 59.3, 60.8, 126.4, 151.4, 160.4 and 162.4; ν max /cm Ϫ1 1732, 1651 and 1615; m/z 185 (M, 33%), 157 (9), 139 (61), 125 (26), 111(13) and 84(6).A trace of ethyl 2-methoxy-4-methyloxazole-5-carboxylate (<1%) was also obtained.Ethyl 2-ethoxy-5-methyloxazole-4-carboxylate 22 (R = Et) Isoxazolone 21 (R = Et) (220 mg) was subjected to flash vacuum pyrolysis (490 ЊC, 150 ЊC, 0.1 mmHg). Material collected in the cold trap was subjected to radial chromatography (diethyl ether-light petroleum, 2 : 3) affording the title compound (56 mg, 31%) as a colourless oil (Found: M ϩ , 199.0847.…”

Total synthesis of noricumazole B establishes d-arabinose as glycan unit

“…Coupling with serine-methylester and ring closure gave oxazolidine which was oxidised to oxazole 8 following Barrish and Singh's procedure. 7 Then, the ester was transformed into the homologised vinyliodide 9 by transferring the intermediate aldehyde into the alkyne using the Bestmann-Ohira reagent 13 8 followed by a hydrozirconation and by ipso-iodination.…”