Study On The Construction Of Sulfur-Containing Heterocyclic Compounds With Elemental Sulfur

Sulfur-containing heterocyclic compounds are functional group skeletons with unique physiological and pathological activities,which widely exist in biologically active molecules.Due to their unique pharmacological and pathological effects,sulfur-containing compounds are widely used in the medicinal treatment of various diseases such as anti-tumor,anti-inflammatory,antibacterial,and anti-diabetic,which has stimulated the strong interest of researchers.However,the construction of conjugated sulfur heterocyclic compounds using base catalysis with readily available starting materials is of great significance in organic synthesis research.In this thesis,we explored the research scheme for the construction of various isothiazole and 2-carbonyl benzo[b]thiophenes compounds using elemental sulfur as the sulfur source without transition metal catalysts.This green-friendly new strategy provides useful guidance for the construction of conjugated sulfur heterocycles.The main contents are as follows:1.A new method for the one-pot synthesis of isothiazoles from readily available substrates with the participation of ammonium chloride（NH₄Cl）and elemental sulfur was developed.A series of substituted 3,5-diphenyl isothiazole compounds were synthesized using NH₄Cl,sulfur and enone,stirred at 130℃for 12 hours in air at mosphere with 41%to 78%yields.The reaction enables efficient formation of successive C-N,C-S,and N-S bonds,providing a facile method for the construction of isothiazoles and enriching the synthesis of sulfur heterocycles.2.A novel method for synthesizing 2-carbonylbenzene/naphtho[b]thiophenes from sulfur,potassium carbonate（K₂CO₃）and halogen-substituted ketenes under metal-free conditions was realized.A series of substituted 2-carbonylbenzo[b]thiophene compounds were synthesized in41%to 78%yields using K2CO3,sulfur,and 2-bromoenone/2-chloroenone at 100°C for 10 h in an air atmosphere.The reaction avoids the use of transition metal catalysts and provides an efficient new way for the synthesis of 2-carbonylbenzo[b]thiophene.3.A novel approach to prepare conjugated sulfur-heterocyclic compounds by alkali-catalyzed coupling cyclization of 2-halogenated aldehydes and ethyl ketones was proposed.This method synthesized a series of 2-carbonylbenzo[b]thiophene compounds in 38%to 85%yields using K₂CO₃,sulfur,2-bromobenzaldehydes and acetophenones at 130°C for 16 h.This strategy develops an efficient strategy for the synthesis of 2-carbonylbenzo[b]thiophenes without transition metal catalysis,which facilitates the construction of conjugated skeletons of sulfides.In this thesis,a novel method for the efficient synthesis of isothiazole and benzo[b]thiophene by the multi-component cyclization of ketone,benzaldehyde and acetophenone using elemental sulfur as sulfur source was established,which provided a strategy for the effective synthesis of conjugated sulfur-heterocyclic compounds from simple and readily available raw materials without transition metal catalysis.