Preparation of Diazenes by Electrophilic C-Coupling Reactions of Dry Arenediazonium o-Benzenedisulfonimides with Grignard Reagents

Abstract

The diaryldiazenes (19 examples) and aryl( tertbutyl)diazenes (3 examples) 3 were prepared by electrophilic C-coupling reactions of dry arenediazonium o-benzenedisulfonimides 1 with Grignard reagents. The reactions were carried out in anhyd THF at -78°C under nitrogen and gave diazenes in 66-91% yield with few exceptions. In all cases the anion precursor of salts 1 , i.e. the o-benzenedisulfonimide, was recovered easily, in greater than 90% yield.It is known 1 that most dry-state arenediazonium salts are a high risk from the point of view of storage and handling, as many physical stimuli such as heat, light, shock, static electricity etc. can lead to their rapid decomposition, occasionally explosively. Such instability has certainly limited the use of these salts in synthetic applications, both on a laboratory scale and, even more so, on an industrial scale. Despite this, three classes of dry-state arenediazonium salts, viz., most tetrafluoroborates and some zinc double chlorides and sulfonates , are considered low risk reagents and are used, though with great caution, both in the laboratory and industrially. From a synthetic point of view one of the advantageous features of dry arenediazonium salts is certainly that of being able to realize reactions in aprotic solvents with various reagents, for example carbanions incompatible with protic solvents. On this subject, among the methods used in the past to prepare azo compounds, various reactions were studied, though not in-depth, using different combinations of dry arenediazonium salts and organometallic reagents, precursors of aryl and tert -butyl carbanions. Reactions specifically studied were those between arenediazonium tetrafluoroborates and Grignard reagents, or organocadmium, -mercury, -lithium, and -zinc reagents, 2, 3 or also between arenediazonium zinc double chlorides and Grignard reagents. [4][5][6][7] The best synthetic results obtained are those related to various reactions between the arenediazonium tetrafluoroborates and diphenylzinc (4 examples, 40-70% yield) 3 or di-tert -butylzinc (1 example, 97% yield), 3 and various reactions between arenediazonium zinc double chlorides and Grignard reagents (4 examples, 72-99% yield). 4 In other cases the reactions either failed completely or gave a maximum yield of 60%; the azo compound yield for most of the considered examples was 1 to 10%.In the course of recent research, we prepared a representative series of dry arenediazonium salts 1 , that were stabilized to an exceptionally high degree by the anion of o -benzenedisulfonimide. Most of these salts can be stored without decomposition for extended periods and are ready for use.In a wide-ranging investigation of the possible synthetic uses of salts 1 , we aimed to prepare azo compounds 3 [diaryldiazenes and aryl( tert -butyl)diazenes] by electrophilic C-coupling reactions of dry salts 1 with Grignard reagents 2 . The reactions were performed by adding equimolar amounts of Grignard reagents to suspensions of salts 1 in anhyd THF at -78°C, under stirring and...

o-Benzenedisulfonimide: An Organic Reagent and Organocatalyst of Renewed Interest

“…In optimal conditions the molar ratio 67 : 126 was 1 : 2, in THF at room temperature. Variously substituted aryldiazenes were obtained in good yields (except for sterically hindered arenediazonium cations), comparable to those previously obtained from the same arenediazonium salts (Scheme 43) [41]. The mechanism previously proposed [44] was used in part also in this case: nucleophilic In the case of trimethylindium 132 only formaldehyde (aryl)hydrazones 135 were obtained.…”

“…The procedure was of general validity and gave high yields of products. In all the reactions, two isomeric products were observed, but complete isomerization of the Z into the E isomer was achieved by heating at 70 °C (Scheme 23) [41]. …”

Azobenzenes—synthesis and carbohydrate applications

“…The synthesis of symmetrical azobenzene derivatives was effected by: (i) oxidation reactions of aromatic primary amines; [19][20][21][22][23][24][25][26][27][28][29][30] (ii) reduction reactions of aromatic compound having nitro groups; [32][33][34][35][36] (iii) diazo-coupling via diazonium salts; [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] and (iv) coupling reactions with arenediazonium salts. 100,101 The synthesis of dissymmetrical azobenzene derivatives was effected by: (i) oxidation reactions of aromatic primary amines; 31 (ii) coupling of primary arylamines with nitroso compounds (Mills reaction); [37][38][39][40][41][42][43][44][45][46]…”

“…100,101 The synthesis of dissymmetrical azobenzene derivatives was effected by: (i) oxidation reactions of aromatic primary amines; 31 (ii) coupling of primary arylamines with nitroso compounds (Mills reaction); [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and (iii) coupling reactions with arenediazonium salts. 100,101 Starting from hydrazo compounds, the oxidation furnished symmetrical azobenzenes 72,73,76,77 and dissymmetrical azobenzenes. 72,73,76,87 Starting from azoxybenzene compounds, the reduction furnished symmetrical azobenzenes [92][93][94][95][96][97][98][99] and dissymmetrical azobenzenes.…”

“…In 1998, Fochi et al developed the synthesis of azobenzene by an electrophilic coupling reaction of arenediazonium salts with Grignard reagents. 100 Thus, treatment of the arenediazonium o-benzenedisulfonimide 120 with a solution of phenylmagnesium bromide (121) afforded azobenzene (1) in 71% yield (Scheme 46).…”