https://doi.org/10.1351/goldbook.A00559
Oxazol-5(4H)-ones I, compounds derived by @C01494@ of N-acyl α-amino @C00852@, RC(=O)NHCR2C(=O)OH, through formal loss of the elements of water. 4-Hydrocarbylideneazlactones II are often referred to as 'unsaturated azlactones'.
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Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1321 [Terms] [Paper]