Study On Ring-opening Reaction Involved By Benzothiazole Derivatives

Benzo[d]thiazoles and their derivatives,as common structural units in biological secondary metabolites,have good biological activity and are widely used in the fields of pesticides,medicines and materials.In recent years,the simultaneous construction of C-S and C-N bonds under transition metal catalysis has led to a great demand for functionally diverse structural motifs.The formation of C-N bonds has attracted widespread attention as one of the most promising research strategies in organic reactions.The benzothiazole we studied is a special five-membered heterocycle containing two different N and S heteroatoms,which has a wide range of applications in agriculture and pharmaceuticals.For example:antitumor drugs,hypoglycemic drugs,diuretics,etc.Therefore,research on new methods to open the ring of benzothiazoles is still an active research area with great impact.The main research contents are as follows:First,an efficient strategy was successfully developed under transition metal-free conditions using acetonitrile as the reaction solvent to synthesize a novel asymmetric sulfonylation via TBAI-catalyzed ring-opening sulfonylation of benzo[d]thiazole and arylsulfonylhydrazide.Thio sulfonate.This transformation utilizes readily available benzo[d]thiazoles as good thiol replacements and affords various asymmetric thiosulfonates in good yields ranging from 35%to 95%.This protocol has the advantages of mild reaction conditions,wide substrate range,and gram-scale synthesis.Meanwhile,asymmetric thiosulfonates as thioarylation reagents react with naphthalene-2-amines to generate a series of novel o-amino-substituted diarylsulfides.Second,the ring-opening alkylation of benzothiazoles with dialkyl carbonates to synthesize a series of N-alkyl-N Reaction of-（o-Alkylthio）phenylamides.This transformation,using green and inexpensive dialkyl carbonates as alkylating reagents,afforded 21N-alkyl-N-（o-alkylthio）phenylamides in 19%-98%yields.Oxidation of N-methyl-N-（2-（methylthio）phenyl）carboxamide using the oxidative properties of m-chloroperoxybenzoic acid afforded the corresponding N-methyl-N-methylN-（2-（methylsulfonyl）phenyl）carboxamide.In addition,N-benzyl-N-（2-（benzylthio）phenyl）formamide was hydrolyzed in NaOH and ethanol to give N-benzyl-2-（benzylthio）aniline in 74%yield.Gram-scale synthesis experiments and further derivatization of alkylated products indicated the potential application of this scheme in synthetic chemistry,and finally a possible reaction mechanism was proposed based on controlled experiments and reports in the existing literature.Finally,using I₂ as catalyst and K₂S₂O₈ as oxidant,the ring expansion of benzothiazole and 3-oxo-3-arylpropionitrile was studied and a variety of 3-aryl-4H-benzo[b][1,4]Thiazine-2-carbonitrile product.Stable and odorless benzothiazoles were used as starting materials for this transformation,and 22 novel 1,4-benzothiazine derivatives were obtained in 37%-98%yields.The method uses metal-free catalysis,has the advantages of a wide substrate range and gram-scale synthesis.To highlight the synthetic utility of 3-aryl-4H-benzo[b][1,4]thiazine-2-carbonitrile,its further transformation,3-pheny l-4H-benzo[b][1,4]Thiazine-2-carbonitrile was oxidized to 3-phenyl-4H-benzo[b][1,4]thiazine-2-carbonitrile 1,1-dioxide under the action of KMnO4,yield 71%.Meanwhile,in the presence of H2O2,the compound 3-（4-fluorophenyl）-4H-benzo[b][1,4]thiazine-2-carbonitrile was oxidized to 3-（4-fluor opheny 1）4H-benzo[b][1,4]thiazine-2-carbonitrilel-oxide in 81%yield,and finally suggested that the reaction may be a free radical reaction.