Hydroxy derivatives with three heteroatoms

These compounds generally exist in carbonyl forms. The oxygen function can be converted into halogen by phosphorus halides. Reactions with electrophiles are quite complex. Thus, urazole (669) reacts with diazomethane quickly to yield (670), which is more slowly converted into (671). Phenylurazole gives (672) however, 4-phenylurazole yields (673). Oxadiazolinones of type (674) can be alkylated at both O- and /V-atoms. 

Reactivity of Five-membered Rings with Two or More Heteroatoms 

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