Pyrazolines, reaction with acids

The methylhydrazone of acetophenone (112) underwent ready reaction with n-butyl-lithium giving the dianion (113) reaction with acid derivatives such acid chlorides or esters resulted in pyrazole (114) formation whereas with aldehydes, pyrazolines were obtained (76SC5). With dichloromethyleneiminium salts (115), 5-dimethylaminopyrazoles... 

Pyrazolin-5-ones can be readily acylated at C-4 with acid chlorides,110 esters1841 and anhydrides.1279 Very few reactions with acid chlorides and esters have been reported but the product is the ketone (XXI), as expected. Phthalic anhydride reacts with two moles... 

The amino group of 4-amino-3-pyrazolin-5-ones reacts normally. Acylation occurs readily with a wide variety of acylating agents. Amides are formed by reaction with acid chlorides,50,533,984,1414,1473 acids618,984,1471 and esters in the presence of phosphorus pentoxide.1471 Thioformamides have been prepared by reaction with dithioformic acid and its salts.472,556,1374 Sulfonyl chlorides react to form sulfonamides.98,489,984,1249,1504 Chlorophosphates react with 4-amino-3-pyrazolin-5-ones to form phosphoramide derivatives.509,1498... 

Owing to the active hydrogen atoms at C-4 in 3,5-pyrazolidinediones various substitutions at C-4 can be accomplished. Reaction with acid chlorides in the presence of aluminum chloride gives 4-acyl-3,5-pyrazolidinediones.919,976 However, if two groups are already present at C-4, the enolic form of the dione is acylated on the oxygen atom to give 3-acyloxy-2-pyrazolin-5-ones.998 Treatment of 3,5-pyrazolidinediones with nitrous acid gives nitrosation at C-4.976 The nitroso... 

Hi) Electrochemical reactions and reactions with free electrons Electrochemical oxidation of 3-methyl-l-phenylpyrazole gave the 3-carboxylic acid whereas electrochemical reduction (Section 4.04.2.1.6(i)) of l,5-diphenyl-3-styrylpyrazole produced the A -pyrazoline (B-76MI40402) with concomitant reduction of the exocyclic double bond (343). 

High vacuum pyrolysis, heating in organic bases, contact with acidic adsorbents and reaction at room temperature with perchloric acid or boron trifluoride etherate cleaves the pyrazoline to give a 45-60% yield of the cyclopropane derivative (13) as well as 9 % of the unsaturated methyl compound (14). ° ... 

Johnson and co-workers also investigated the general acid-catalyzed diazomethane reaction with benzalacetone (20). When treated with 3 mole-equivalents of diazomethane, the latter is converted to the A -pyrazoline... 

Diphenylcyclopropane has been prepared in 24% yield by the Simmons-Smith reaction,2 in 78% yield by treatment of 3,3-diphenylpropyltrimethylammonium iodide with sodium or potassium amide,3 in 61% yield by reaction of 1,1-diphenyl-ethylene with dimethylsulfonium methylide,4 and in unspecified yields from 1,1-diphenylethylene by reaction with diazomethane followed by pyrolysis of the resulting pyrazoline or by reaction with ethyl diazoacetate followed by distillation of the corresponding acid over calcium oxide.5... 

Arenes, polyalkyl, oxidation with per-oxytrifluoroacetic acid and boron trifluoride, 48, 89, 90 Arenesulfonyl chlorides, reaction with 3-amino-3-pyrazoline, 48, 11 Aromatic aldehydes. Mesitalde-HYDE, 47, 1... 

A number of 2-acyI-l-chIoroethenes add to DPD in ether, losing HC1 spontaneously from the intermediate pyrazolines, and giving l/f-pyrazoles from rearrangement of the transient 3H isomers.50,60 The acid chloride 36 gives a small amount of a 3//-pyrazoIe 37 from reaction with two moles of methyl diazoacetate (Scheme 12).88... 

Camera and co-workers (287) described the 1,3-dipolar cycloaddition of trimethylsilyldiazomethane 171 with 165 (Note Opposite enantiomers are shown here). The intermediate 1-pyrazoline obtained from this reaction rearranged after acidic work up to furnish the 2-pyrazolines 172 with 80-88% de (Scheme 12.52). By further conversion of these products, optically active azaprolines were synthesized. 

Pyrazolines containing aryl substituents with some functional groups can be used in the synthesis of new heterocycles. For example, the reaction of 5-(2-hydrohyphenyl)pyrazolines 111 with noncyclic 112 or cyclic carbonyl compounds under acidic conditions yields dihydropyrazolo[l,5-c]-l,3-benzox-azines 114 and 115, respectively [167, 168, 169] (Scheme 2.30). 

The 5-hydrazino-l,2,4-thiadiazoles (152) are stable in acid and base and readily form hydrazone derivatives on reaction with suitable carbonyl compounds. Thus, (152 R = Me, Ph, m-02NC6H4) reacts with /3-keto esters to form 3-alkyl-l-(l,2,4-thiadiazol-5-yl)pyrazolin-5-ones (161) which undergo coupling with p-nitrosodialkylanilines to form azomethine dyes (162) (65AHC(5)119>. 

The [3 + 2] cycloadduct formed on treatment of tetrakis(trifluoromethyl)-Dewar-thiophene with trifluoromethyl diazomethane isomerizes to give an annulated 3-trifIuoromethyl-l//-2-pyrazoline in the presence of acids and bases. Sulfur can be removed from both compounds on reaction with triphenylphosphine (80JA6633). 

The usual procedure for preparing the 5-oxo-2-pyrazolin-3-carboxylic acids is reaction of oxaloacetic acid or esters with hydrazines (eq. 225). Several modifications of this reaction have been used. The... 

A variety of 2-pyrazolin-5-ones having carboxyl or carboxyl derivatives as substituents and a second functional group are known (Table XXXIII). Such compounds are usually prepared by methods already described, and only those compounds having an arylazo substituent as the second functional group will be discussed. These compounds have been extensively investigated because of their commercial importance as dyes. The important dye tartrazine is of this class. It is the trisodium salt of 4-(4-sulfophenylazo)-l-(4-sulfophenyl)-5-oxo-2-pyrazolin-3-carboxylic acid. These dyes exist largely as enol isomers. The principal means of preparation is coupling of a diazonium salt with a 5-oxo-2-pyrazolin-3-carboxylic acid or its derivatives. Another important preparation of these compounds (eq. 231) is by the reaction of... 

Also shown in the same equation is the synthesis of esters by the reaction of 3-pyrazolin-5-ones with carbon disulfide and either ethyl bromide or ethyl chloroformate in the presence of aluminum chloride.89,109 The monothio acids have been synthesized by reaction of acid chlorides with hydrogen sulfide.109 Kocwa826,829,830,831 has studied the preparation of amides and hydrazides of these thio acids and found that two types exist. In one type the compounds are thioamides but in the other they are iminothiolic acids. Treatment... 

Oxo-3-pyrazolin-4-sulfonic acids (Table XXXVI) are prepared by direct sulfonation738,745 with sulfuric acid and acetic anhydride or by chlorosulfonation with chlorosulfonic acid, followed by hydrolysis to the acid.1248,1249 The reaction of 2,3-dimethyl-l-phenyl-5-oxo-3-pyrazolin-4-sulfonyl chloride with urea forms a bis(5-oxo-2-pyrazolin-4-sulfonic acid) derivative,1249 the only such bis derivative reported. Reduction of the sulfonic acid chlorides with zinc and acid forms the corresponding mercapto compound.1249... 

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