Benzothiophenes And Benzothiazoles Synthesis Using Elemental Sulphur As The Sulphur Resource

Heterocyclic derivative compounds occupy a pivotal position in organic compounds in terms of quantity or types of use. Benzo-heterocyclic compounds are one of most important members of heterocyclic compound because of their special biological activity and large conjugated structure. 2-Substituted benzothiophenes are the basic skeleton of Zieuton, Benocyclidine, Raloxifene, Arzoxifene and a series of drugs. In addition, benzothiophene derivative are also applicable to the field of optoelectronic materials. Aryl substituted benzothiazole showed a wide range of biological activity, anti-tumor, anti-viral and anti-bacterial aspect, showing excellent effect. What’s more, basic structural unit of benzothiazole can be found in natural products, functional materials, industrial dyes and agricultural chemicals. Based on these, in heterocyclic compound evolving process, a large number of synthesis methods both types of compounds mentioned above have been found. Since benzothiophenes and benzothiazoles are widely used in the medical field, research on synthesis methods of these two types of compounds without the use of transition metal catalyzed are very important. This paper studied the research on synthesis methods of benzothiophenes and benzothiazoles using elemental sulfur as sulfur source without using a transition metal, the main work as below:1. The synthisis of 2-arylbenzothiophene in the promoting of inorganic bases, three-component reaction of o-halogenbenzaldehyde, aromatic acetates and elemental sulfur under milder conditions intermolecular cyclization was described. This method avoided using transition metal and the use of inorganic bases could promote the carbanion generated with the hydrogen halide produced by cyclization neutralized at the same time. The product was easy to separate and purify since the inorganic or organic compounds with low boiling point as byproduct. In contrast, this method avoided the use of organic sulfur reagents with sick odor and provided a new path for the synthesis of benzothiophene compounds.2. p-Toluidine, styrene, and elemental sulfur promoted by a catalytic amount of elemental iodine and acetic acid together to yield 6-methyl-2-phenyl-benzothiazole. Offer to participate in the intermolecular cyclization of p-toluidine and sulfur to generate the corresponding product after cleavage of the carbon-carbon double bond of styrene in the system. Compared to the previous work, the advantages of this method were calling for lower substrates without two functional groups on benzene ring, the use of a more readily available and inexpensive aryl amines as raw material, while avoiding using transition metals and organic sulfur reagent.