Heterocyclic compound

A heterocyclic compound is a compound of a cyclic skeleton structure composed of a carbon atom and a non-carbon atom. These non-carbon atoms are collectively referred to as heteroatoms, and common heteroatoms are nitrogen, oxygen, sulfur, and the like. The compounds such as lactones, lactams, and cyclic ethers which have been studied before are all heterocyclic compounds, but the properties of these compounds are similar to those of the same type of open chain compounds, and are therefore discussed in the corresponding sections. This chapter will mainly discuss heterocyclic compounds, ie aromatic heterocyclic compounds, which are relatively stable in ring system and have a certain degree of aromaticity. There are many kinds of heterocyclic compounds, and the number is large. It is widely distributed in nature, and many natural heterocyclic compounds play an important physiological role in animals and plants. For example: chlorophyll in plants, hemoglobin in animal blood, active ingredients alkaloids and some glycosides in Chinese herbal medicines, some antibiotics and vitamins, certain amino acids and nucleotide bases of constituent proteins all contain heterocyclic rings. structure. In the existing drugs, about half of the heterocyclic structures are contained. Therefore, heterocyclic compounds play an important role in organic compounds, especially organic drugs. Among the heterocyclic compounds, 5-membered and 6-membered heterocyclic rings and their fused heterocyclic compounds are most common and most important. Therefore, according to the size of the ring, the heterocyclic compound can be classified into two major classes of a five-membered heterocyclic ring and a six-membered heterocyclic ring. For example, the above furan, thiophene, pyrrole, oxazole, imidazole and fused ring compounds thereof, benzimidazole, dibenzofuran, etc. are all five-membered heterocyclic compounds, and pyridine, pyrimidine and their fused ring compound quinolin The porphyrin, quinazoline and the like are all six-membered heterocyclic compounds. In the five- and six-membered heterocyclic compounds, according to the number of heteroatoms in the ring, it can be divided into a heterocyclic ring containing one hetero atom and a hetero ring containing two or more hetero atoms. For example, furan, thiophene, pyridine, hydrazine, quinoline, dibenzofuran, etc. are heterocyclic compounds containing one hetero atom; imidazole, pyrimidine, benzimidazole, quinazoline, etc. are heterocyclic compounds containing two hetero atoms. And hydrazine is a heterocyclic compound containing two or more, that is, a plurality of hetero atoms. The heterocyclic compound can be classified into a single heterocyclic ring and a fused heterocyclic ring according to the form of a ring in the molecule. For example, furan, pyridine, pyrimidine, imidazole and the like are all monoheterocyclic rings, and hydrazine, quinoline, dibenzofuran, anthracene and the like are fused heterocyclic compounds.