In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called A convenient and exclusive methoxybromination of alkenes, published in 1976-02-29, which mentions a compound: 65090-78-0, Name is 2-Bromo-3-methoxypropanoic acid, Molecular C4H7BrO3, Electric Literature of C4H7BrO3.
Alkenes R1CR2:CR3R4 (e.g., R1 = Ph, p-tolyl, H; R2 = H, Me; R3 = HCO2Me; R4 = CO2Me, H) were methoxybrominated with Br in MeOH in the presence of AgNO3, Pb(NO3)2 or yellow Pb oxide (which one depended on the nature of the alkene). Cyclohexene was methoxyiodinated similarly in the presence of AgNO3. Electrophilic addition of the elements of MeOBr was general. The trans and stereospecific nature was established by studying dehydrobromination of methoxybromoadducts under E2 elimination conditions.
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Reference:
Pyrimidine | C4H4N2 – PubChem,
Pyrimidine – Wikipedia