The synthesis of oxazoles by thermolysis or photolysis of 2-acylisoxazol-5-ones
作者:Kiah H. Ang、Rolf H. Prager、Jason A. Smith、Ben Weber、Craig M. Williams
DOI:10.1016/0040-4039(95)02240-6
日期:1996.1
N-acylisoxazol-5-ones are converted into the corresponding 2-substituted oxazoles by photolysis at 300 or 254nm, or by flash vacuum pyrolysis. The former procedure is favoured for isoxazolones with electron withdrawing groups at C-4, and pyrolysis for all others.
Chemistry of 5-oxodihydroisoxazoles. Part 17.1 Acylation of 5-oxodihydroisoxazoles
作者:Rolf H. Prager、Jason A. Smith、Ben Weber、Craig M. Williams
DOI:10.1039/a700133i
日期:——
2-Unsubstituted isoxazol-5(4H)-ones and
-5(2H)-ones may be acylated by acid chlorides,
anhydrides or carboxylic acids in the presence of carbodiimides, to give
O- and N-acylated products. The solvent, the presence
of base and the temperature are found to alter the product ratios
dramatically, but the substituents present at C-3 have the greatest
effect. Aliphatic acid anhydrides and chlorides generally react at
nitrogen, but aroyl halides give significant proportions of
O-acylated products. Limited success in converting
O-aroyl to N-aroyl isoxazolones is reported.
Chemistry of 5-oxodihydroisoxazoles. Part 18.1 Synthesis of oxazoles by the photolysis and pyrolysis of 2-acyl-5-oxo-2,5-dihydroisoxazoles
作者:Rolf H. Prager、Jason A. Smith、Ben Weber、Craig M. Williams
DOI:10.1039/a700134g
日期:——
N-Acylisoxazol-5-ones lose carbon dioxide under
photochemical and thermal conditions affording iminocarbenes which
undergo intramolecular cyclisation through the oxygen of the acyl group
to give oxazoles. Under photochemical conditions those acylisoxazolones
with electron withdrawing groups at C-4 usually give high yields of
oxazoles, while those with electron donating groups at C-4 give only
poor yields: the reverse is observed under thermal conditions.