Diazonium, reaction with hydrazones

Whereas reaction of hydrazones disubstituted in the 4,5-position of the selenazole rings with diazotized arylamines only gives formazans, compounds unsubstituted in the 5-position can be attacked there by the diazonium cation. In fact, the azo coupling in this position is decidedly quicker reaction of 5-benzylidenehydrazino-4-phenyl-... 

Several interesting reactions have been described for quinolizine-3-diazonium tetrafluoroborate 121. Thus, its treatment with secondary amines gave the corresponding triazenes 122 <2004ZNB380>, while its reaction with 1,3-dicarbonyl compounds gave the corresponding hydrazones. In the case of alkyl 4-chloro-3-oxobutanoates, the intermediate hydrazone 123 furnished a pyrazole derivative 124, as shown in Scheme 17 <2002H(57)2091>. 

Almotnptan (5, LAS-31416) was discovered and developed by Almirall in Spain. The U.S. marketing rights were licensed to Pharmacia and then to Janssen. The synthesis commenced with the reaction of (p-nitrophenyl)-methanesulfonyl chloride (57) with pyrrolidine, followed by hydrogenation of the nitro group to give aniline 58 (Scheme 21). The hydrazine 59 was prepared by diazotization of 58 followed by reduction of the resulting diazonium salt with stannous chloride. Hydrazine 59 was treated with 4-chlorobutanal diethyl acetal in aqueous HCl and hydrazone 60 precipitated and was... 

The most frequently used method of this type is the reaction of hydrazones (247) with diazonium compounds to afford formazans (248). These can be cyclized with carbonyl compounds in the presence of acid to yield verdazylium cations (252) which are reduced under basic conditions to give the verdazyls (253) which can be further reduced to the tetrahydro-l,2,4,5-tetrazines (254). The formazans (248) can be alkylated and the alkylfor-mazans (249) cyclized by heating or treatment with a base to form the tetrahydrotetrazines (250). It is not necessary to isolate the alkylated compounds (249) the complete reaction (248-250) can be carried out at room temperature in the presence of barium oxide or hydroxide in DMF. Oxidation of (250) provides a synthesis of verdazyls (251) (see Section 2.21.3.4.2). 

Synthesis of the copper complex31 [167780-70-3] (H, Na salt) involves coupling of a diazonium compound with a hydrazone [54] 2-(3-amino-4-hydroxyphe-nylsulfonamido)chlorobenzene is dissolved in hot water, to which dilute NaOH solution is then added. After addition of sodium nitrite, the solution is cooled to -5 °C and then added to a well-stirred mixture of HC1, water, and ice. The diazonium salt suspension is neutralized with NaHC03 and combined with the weakly acidic solution of the hydrazone formed with 2-hydrazino-5-sulfobenzoic acid and benzaldehyde in water. The reaction mixture is kept at 0-10 °C, and at pH 10-12 by dropwise addition of diluted NaOH. When the coupling is complete, the pH of the formazan solution is reduced to 8 with HC1, a dilute aqueous solution of copper tetraaminosulfate is added and the solution is stirred for several hours. The copper complex 31 is precipitated at 85-90 °C with NaCl, then filtered and dried. The resulting powder colors wool in clear, fast blue tones. 

There is clearly a Fischer indole synthesis in the second step but the first step makes the usut. hydrazone in a most unusual way. The first reaction is diazotization so we have to combine fi diazonium salt with the enolate of the keto-ester. That creates a quaternary centre and the KC H deacylates it to give the aryl hydrazone needed for the Fischer reaction. 

Serotonin has been synthesised by several routes the method shown relies on a Fischer indole synthesis, the requisite aryl-hydrazone being constructed by a process known as the Japp-Klingemann reaction in which the enol of a 1,3-dicarbonyl compound is reacted with an aryl-diazonium salt, with subsequent cleavage of the 1,3-dicarbonyl unit. 

Diazotization of 4-[(4-aminophenyl)sulfonamido]-2,6-dimethyl pyrimidine 10, followed by coupling of the diazonium salt with ethyl 3-oxobutanoate 11a or l,3-diphenyl-l,3-propanedione lib, afforded hydrazones 12a,b. Reaction of hydrazone 12a with aminoguanidine nitrate in refluxing acetic acid yielded the pyrazol-3-one 13a in 55% yield (00JIC42) (Scheme 4). 

Sodium acetate Japp-Klingemann reaction with hydroxymethylene compounds Hydrazones from diazonium salts... 

In addition to the above reactions, a number of additional tests for amino compounds, important in special cases, have been worked out. For primary aliphatic and aromatic amines the reaction with o-diacetylbenzene (24) is very suitable. Instead of diazonium salts, hydrazone of 3-methyl-2-benzo-thiazole and ferric chloride can be used for the detection of aromatic amines... 

Oxidative Couplings of Heterocyclic Hydrazones. This method has opened the way to the preparation of azo derivatives of diazo compounds unobtainable by other means, ie, heterocycHc compounds ia which the diazotizable amino group is conjugated with the heterocycHc nitrogen atom as ia 2- and 4-amiQopyridine, compounds which do not normally yield stable diazonium salts (38). The reaction occurs as illustrated by equation 7 for the iateraction of (A/-methylcarbostyryl)hydrazone [28219-37-6] and dimethyl aniline the overall process is oxidation. 

The most important synthesis of pyrazolones involves the condensation of a hydrazine with a P-ketoester such as ethyl acetoacetate. Commercially important pyrazolones carry an aryl substituent at the 1-position, mainly because the hydrazine precursors are prepared from readily available and comparatively inexpensive diazonium salts by reduction. In the first step of the synthesis the hydrazine is condensed with the P-ketoester to give a hydrazone heating with sodium carbonate then effects cyclization to the pyrazolone. In practice the condensation and cyclization reactions are usually done in one pot without isolating the hydrazone intermediate. 

Guanyl hydrazones (18) react with diazonium salts to yield a special class of formazans called guanazyls, e.g., 19 (Eq. 1).20 22 The reaction is... 

The reaction of (tht)AuC6F5 with the diazonium compound Ph2CN2 is also very complex and yields an adduct of a hydrazone, probably via the carbene Ph2C as an intermediate (Equation (28)).145... 

---