The reaction between dry arenediazonium o-benzenedisulfonimides 1 and sodium thiolates in anhydrous methanol represents an efficient and safe procedure, of general validity, for the preparation of unfunctionalized or variously functionalized alkyl aryl and diaryl sulfides. As a rule, the reaction temperature was maintained at 0-5 degrees C for the alkylthiodediazoniations and at room temperature (20-25 degrees C) for the arylthiodediazoniations. The sulfide yields are generally high; of the 63 considered examples, 43 gave yields greater than 80% and 13 were between 70% and 80%. Lower yields were obtained only when sterically hindered diazonium salts or thiols were used. A good amount of the o-benzenedisulfonimide (8) was always recovered from the reactions and could be reused to prepare salts 1. The copious experimental data collected in homogeneous conditions have offered several starting points for the study of the mechanism of these reactions.
Aryl thiocyanates 3 (22 examples) were easily prepared by reaction of dry arenediazonium o-benzenedisulfonimides 1 and sodium thiocyanate (2) in anhydrous acetonitrile at room temperature (20-25°C) in the presence of copper powder (Procedure A) and at 50°C or room temperature without the metal catalyst (Procedure B). The yields were from very good to excellent in Procedure A (average yield = 83%), and from modest to excellent in Procedure B (average yield = 63%). In comparison with the thiocyanodediazoniation carried out under traditional Sandmeyer-type conditions, the yields of 3 were higher and the isothiocyanate isomers were formed only in traces. Moreover, the results obtained in the absence of copper confirm the role of the anion of salts 1 as an electron transfer agent.The importance of aryl thiocyanates 3 lies in both their biological properties 1,2 and their use as a versatile starting material for a variety of sulfur-containing compounds, 3,4 like aryl sulfonyl cyanides, sulfonic acids, sulfonyl chlorides, sulfides, disulfides, thiocarbamates, thiolesters and, especially, thiols and heterocycles, and the procedures for their synthesis are numerous. 3,5,6 The most traditional route for obtaining aryl thiocyanates 3 is that of diazotized primary aromatic amine reactions with metal thiocyanates in aqueous solution, mostly under Sandmeyer-type conditions. 3,5,7 The yields, quite often unsatisfactory, the concomitant formation of various by-products, including the aryl isothiocyanate isomers and, finally, the nucleophilic displacement of other substituents present on the aromatic ring, promoted by the activating effect of the diazonium group, are the well known limitations of this synthetic route. 3,5 Our recent research 8 has resulted in a new, quite large, family of dry state diazonium salts, the arenediazonium o-benzenedisulfonimides 1. Due to their exceptional properties, they have great potential for numerous synthetic applications. In fact, salts 1: i) can be easily prepared and isolated in the dry state; ii) are, with few exceptions, extremely stable and can be stored, ready for use, for unlimited times; iii) react, apart from in water, also easily in organic aprotic solvents, allowing reaction with reagents sensitive to protic solvents; iv) permit, at reaction end, the easy recovery and reuse of o-benzenedisulfonimide; v) supply, in the various synthetic applications studied, the expected reaction products in greater yield than can be achieved with reactions in traditional conditions; vi) contain an anion that, in particular conditions, acts as an electron transfer agent and is itself able to perform catalytic activity.As a follow-up to previous work that was aimed at studying the synthetic applications of salts 1, the present work reports the results concerning the preparation of aryl thiocyanates 3 by reaction of dry arenediazonium o-benzenedisulfonimides 1 with sodium thiocyanate (2), operating in both the presence and absence of copper powder (Scheme 1). The Table shows the operating conditions of...
This research comprises three parts. The first part regards the synthesis of 1-aryl-3,3-dialkyltriazenes 3 by reaction of dry arenediazonium o-benzenedisulfonimides 1, also coming from weakly basic aromatic amines with dimethylamine or diethylamine in aqueous solution at 0-5°C. Yields were usually greater than 90% and there was the possibility of recovering the o-benzenedisulfonimide (5), which could be reused to prepare the salts 1. In the second part it was demonstrated that there is the possibility of reconverting the triazenes 3 into the starting stable dry salts 1 by using 5 as acid. The reactions were carried out in glacial acetic acid at 50-55°C and normally afforded salts 1 in yields of around 90-99%. The third part concerns the setting up of two procedures for the conversion of 3 to aryl iodides 9, bromides 10 and chlorides 11. Procedure A used the corresponding aqueous hydrogen halides in acetonitrile at r.t. or 60°C, sometimes in the presence of aqueous HBF 4 , sometimes Cu powder (25 examples, yields 65%-88%). Procedure B usually used anhydrous methanesulfonic acid and tetraalkylammonium halides in anhydrous acetonitrile at temperatures varying from r.t. to 80°C, sometimes in the presence of Cu (16 examples, yields 65-88%).Triazenes are a class of compounds of great interest. 1 Their biological activity has been and still is, the subject of numerous studies; several triazenes are chemotherapeutic agents active against bacterial and especially, protozoal infections, while the 1-aryl-3,3-dimethyltriazenes possess significant in vivo anti-tumor activity. For example, wide therapeutic use is made of dacarbazine, i.e. 5-(3,3-dimethyltriazeno)imidazole-4-carboxamide, as an active principle against human malignant melanoma. Still in the medical field, triazenes are used in the preparation of radiolabeled materials, used as tracers in diagnostic procedures. In technological applications, the ability of triazenes to break down to yield, in situ, diazonium ions with coupling properties is widely used to produce insoluble azo dyes directly on natural and synthetic fibres. Finally, the triazene group plays a significant role in organic synthesis, being a protected form for both the diazonium group and hence for all the functional groups deriving from it and for the aromatic and aliphatic amines from which it arose.It was within a wider investigation aimed at evaluating the synthetic potential of the dry arenediazonium obenzenedisulfonimides 2 1 that the present research was undertaken, it consists of three parts: i) the setting up, based on the use of dry arenediazonium o-benzenedisulfonimides 1, of a simple synthetic procedure for 1-aryl-3,3-dialkyltriazenes 3, also valid for the preparation of unknown or difficult to obtain compounds; ii) break down of the triazenes 3 to the starting dry salts 1; iii) realisation of efficient procedures for converting, in aqueous or anhydrous organic solvents, the 1-aryl-3,3-dialkyltriazenes 3 into aryl iodides, bromides and chlorides, via the corresponding arenediazonium salt ...
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