Cycloadditions. 48. Novel heterocycles by bis heteroannulation of oxazoles
摘要:
We report the first examples of intramolecular Diels-Alder addition of heterodienophiles N = N, C =N, C = O, C = S to oxazoles. The required 5-ethoxy- and 5-phenyloxazoles were synthesized bearing a side chain of variable length on C-2 to which the different heterodienophiles are attached. The products of the thermal bis heteroannulation are 3-triazolines, imidazolines, oxazolines, or thiazolines fused to a five- to six-membered ring. Relative reactivities were established and the mechanism is discussed.
Cycloadditions. 50. Multipath reactions between intramolecularly formed oxazolium salts and nucleophiles
作者:Alfred Hassner、Bilha Fischer
DOI:10.1021/jo00037a023
日期:1992.5
Reaction of 2-(4'-bromobutyl)-5-ethoxyoxazole (1) with nucleophiles led either to S(N)2 substitution products or to products with a piperidine skeleton. The latter were shown to arise from an intramolecular ring closure to an oxazolium salt 7, which was faster in the presence of a catalytic amount of NaI and in a polar solvent and for which NMR evidence is presented. The further transformation of 7 to 3-6 apparently involves addition of nucleophiles to 7 to produce 4-oxazoline 8 which opens to azomethine ylide 9. Neutralization of the latter occurred either via a proton shift, an alkyl shift, or via trapping by a dipolarophile (electron poor or electron rich). FMO calculations explain the preferred regiochemistry observed during trapping of ylide 9b.
Intramolecular formation of oxazolium salts and their reaction with N- and C-nucleophiles.
作者:Alfred Hassner、Bilha Fischer
DOI:10.1016/s0040-4039(00)97282-4
日期:1990.1
HASSNER, ALFRED;FISCHER, BILHA, TETRAHEDRON LETT., 31,(1990) N9, C. 7213-7214
作者:HASSNER, ALFRED、FISCHER, BILHA
DOI:——
日期:——
Cycloadditions. 48. Novel heterocycles by bis heteroannulation of oxazoles
作者:A. Hassner、B. Fischer
DOI:10.1021/jo00010a044
日期:1991.5
We report the first examples of intramolecular Diels-Alder addition of heterodienophiles N = N, C =N, C = O, C = S to oxazoles. The required 5-ethoxy- and 5-phenyloxazoles were synthesized bearing a side chain of variable length on C-2 to which the different heterodienophiles are attached. The products of the thermal bis heteroannulation are 3-triazolines, imidazolines, oxazolines, or thiazolines fused to a five- to six-membered ring. Relative reactivities were established and the mechanism is discussed.
Fischer, Bilha; Hassner, Alfred; Wolk, Joel L., Acta Chemica Scandinavica, 1993, vol. 47, # 2, p. 191 - 195