| N-heteroaromatic compounds,especially quinoline derivatives,are important raw materials which constitute life,and play important roles in agricultural and pharmaceutical chemistry.So far,various synthetic strategies have been developed for introducing functional groups into the ortho position of quinoline ring to prevent detoxification,which can result in dramatic decrease in therapeutic activities.As versatile synthetic intermediates,sulfones exert a wide range of physical,chemical and biological activities.However,the conventional methods for synthesizing 2-sulfonoquinoline are limited.Therefore,developing a fast,efficient and environmentally friendly method to synthesize 2-sulfonyl quinoline is of great importance from the view of organic synthesis.Organic transformation that involves functionalization of C-H bond is a highly attractive synthetic strategy with easy operation,high step-and atom-economy in covalent synthesis.In the past few years,numerous synthetic strategies concerning direct functionalization via transition metal-catalyzed C-H bond activation have been developed.However,from eco and environmentally friendly view,innovative metal-free synthetic approaches should be strongly pursued.According to the reported literatures,the synthesis of those 2-sulfonyl quinoline mainly include:(1)synthesis of 2-sulfonyl quinoline N-oxides from quinoline N-oxides with sulfonyl chlorides via copper-catalyzed C-H activation.However,the reaction needs metal catalysts,and a harsh reagent(PCl3)should be needed to reduce the 2-sulfonyl quinoline N-oxides to the required 2-sulfonyl quinolines;(2)H-phosphonate-mediated synthetic strategy for the synthesis of 2-sulfonyl quinolines,but its need stoichiometric amount of H-phosphonate for the transformation;(3)synthesis of 2-sulfonyl quinolines from quinoline N-oxides,activated by NaI/TBHP or I2/H2O2,but these methods need stoichiometric amount of iodine-related for the transformation.In particular,many published reports have indicated that iodine-related catalytic transformations in most cases can be performed without the use of noble metal and even toxic metal catalysts,which show the advantage of environmental sustainability.In recently years,molecular iodine,has already developed as an inexpensive,easily available and environmentally benign catalyst for numerous synthetic transformations.However,up to now,there are still some drawbacks in the synthesis of 2-sulfonyl quinolines,such as the use of metal catalysts,higher temperatures,longer reaction times,addition of a large amount of oxidizing agents or additives,and so on.Herein,we have developed a straight forward method by which a wide variety of 2-sulfonyl quinolines were synthesized via C-H bond activation,by a one-pot reaction of quinoline N-oxides with widely available sodium sulfinates in the presence of small amounts of I2.Compared with literature methods,great advantages of this strategy include an efficient time-saving one-pot procedure,extremely mild and metal-free reaction conditions and a wide range of reaction substrates.Finally,we comprehensively expound the mechanism of the reaction by using the designed experiments.The main contents of this paper are as follows:1.The previous catalytic synthetic reaction within iodine reagents and the orientation synthesis and application of 2-sulfonylquinoline derivatives were summarized.2.We disclosed a novel TBAI-mediated synthetic strategy for synthesizing 2-sulfonyl quinoline derivatives by reacting quinoline N-oxides with sulfonyl chlorides.And 6 coupled compounds were synthesized with structural elucidation by 1H NMR、13C NMR and HRMS.3.From the propose mechanism,TBAI and sulfonyl chloride could form iodine and sulfinate,which would be able to promote the sulfonylation of quinoline N-O.So,a novel synthetic strategy for iodine-mediated sulfonylation of quinoline N-oxides has been developed for synthesizing a wide variety of 2-sulfonyl quinoline derivatives by reacting various quinoline N-oxides with different kinds of sodium sulfinates in the presence of small(much less than stoichiometric)amounts of I2 。The reaction conditions were optimized from the respects such as variety of iodine source,ideal amount of iodine source,the amount of reaction substrates,the influence of various solvent with the template reaction of quinoline N-oxide and sodium benzenesulfinate.Under the optimized conditions,the scope and regularity of this reaction were investigated.To our delight,this method could well be applied to both of aryl and alkyl sodium sulfinates,the different substituent of quinoline N-oxides and isoquinoline N-oxides.And 24 coupled compounds were synthesized with structural elucidation by 1H NMR、13C NMR and HRMS.4.We studied the mechanism of this reaction by using radical scavengers,nitrogen protection and designed experiments. |
