Diazo-compounds preparation

The diazo compound prepared in this way from aniline hydrochloride can not be isolated, as it is soluble in water and decomposes when an attempt is made to obtain it by evaporation of the solution. In the use of diazo compounds to prepare other substances it is, in general, unnecessary to isolate them and the reactions are, accordingly, carried out in aqueous solution. When it is desired to obtain the diazo compounds in pure condition, they are prepared in a different way. In this method the salt of the amine is suspended in alcohol and treated either with amyl nitrite or with the oxides of nitrogen formed by heating arsenous acid with nitric acid. When reaction is complete, ether is added to precipitate the salt of the diazo compound, which is obtained in crystalline condition. 

Para Red is usually dyed by passing the fabric which has been treated with jS-naphthol and dried through an ice-cold solution of the diazo compound prepared from p-nitroaniline. Dyes which are applied in this way are often called ice-colors. Para red is very stable and is used in the manufacture of certain varieties of bright red paint. 

Diarylalkynes The anion (1) of this diazo compound, prepared with n-butyllithium (or potassium t-butoxide) in THF at low temperatures, converts diaryl ketones into diarylalkynes in high yield (equation I). Heteroaromatic ketones behave in the same way, but only very electrophilic aryl aldehydes... 

Other literature methods not described in detail here, utilise glycosyl sulfenate [41], thiopseudourea [42], xanthate [42, 43], thiocyanate [44, 45] and dithioacetal [44, 46] intermediates or rely on radical addition to thiohemiacetals [47, 48] or thermal decomposition of diazo compounds prepared by reacting 1-thioaldoses and aryl diazonium salts [44]. Some of these procedures have specific advantage in some specific cases, e.g. the dithioacetal to thioglycoside route is valuable for preparing 1-thio-hexofuranosides [46, 49]. 

Aromatic nitriles (or aryl cyanides) can be obtained by methods (1) and (3). but not by method (2). In addition, aromatic nitriles can be prepared by two other methods, (a) from the corresponding diazo compound by Sandmeyer s Reaction (p. 189), (b) by fusing the corresponding sulphonic acid (or its salts)... 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

Hofmann (1), of the Zurich School, was the first to have tried unsuccessfully to prepare the unsubstituted parent compound, selenazole much later, in 1955, Metzger and Bailly (2) were equally unsuccessful in trying to prepare selenazole from 2-aminoselenazole by reduction of the diazo compound,... 

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. 

Fast Color Salts. In order to simplify the work of the dyer, diazonium salts, in the form of stable dry powders, were introduced under the name of fast color salts. When dissolved in water they react like ordinary diazo compounds. These diazonium salts, derived from amines, free from solubilizing groups, are prepared by the usual method and are salted out from the solutions as the sulfates, the metallic double salts, or the aromatic sulfonates. The isolated diazonium salt is sold in admixture with anhydrous salts such as sodium sulfate or magnesium sulfate. 

A large number of pyridazines are synthetically available from [44-2] cycloaddition reactions. In one general method, azo or diazo compounds are used as dienophiles, and a second approach is based on the reaction between 1,2,4,5-tetrazines and various unsaturated compounds. The most useful azo dienophile is a dialkyl azodicarboxylate which reacts with appropriate dienes to give reduced pyridazines and cinnolines (Scheme 89). With highly substituted dienes the normal cycloaddition reaction is prevented, and, if the ethylenic group in styrenes is substituted with aryl groups, indoles are formed preferentially. The cycloadduct with 2,3-pentadienal acetal is a tetrahydropyridazine derivative which has been used for the preparation of 2,5-diamino-2,5-dideoxyribose (80LA1307). 

This synthetic appproach has been used in a few cases for the preparation of pyridazines from diazo compounds and cyclopropenes. In general, cycloadducts (176) are formed first and these rearrange in the presence of acid or alkali to pyridazines (Scheme 98) (69TL2659, 76H(5)40l). Tetrachlorocyclopropene reacts similarly and it was found that the stability of the bicyclic intermediates is mainly dependent on substitution (78JCR(S)40, 78JCR(M)0582>. 

Pyrazoles are formed when the diazo compounds react with alkynes or with functionalized alkenes, viz. the enols of /3-diketones. Pyrazolenines (353 Section 4.04.2.2.1) are isolated from disubstituted diazomethanes. Many pyrazoles, difficult to obtain by other methods, have been prepared by this procedure, for example 3-cyanopyrazole (616) is obtained from cyanoacetylene and diazomethane (7iJCS(C)2i47), 3,4,5-tris(trifiuoromethyl)pyrazole (617) from trifluorodiazoethane and hexafluoro-2-butyne (8lAHC(28)l), and 4-phenyl-3-triflylpyrazole (618 R =H) from phenyltriflylacetylene and diazomethane (82MI40402). An excess of diazomethane causes iV-methylation of the pyrazole (618 R = H) and the two isomers (618 R = Me) and (619) are formed in a ratio of 1 1. 

A formal ring enlargement of diazirines to five-membered rings is also observed with some hydrazones of ketodiazirines (65CB2509). On attempted preparation of hydrazones (201) from ketodiazirine (200) at 0 C the diazo compounds (202) are plausible intermediates since their transformation to aminotriazoles (203) is known. 

The three types of three-membered ring are also accessible by photoisomerization of open chain 1,3-dipoles nitrones, azomethinimines and linear diazo compounds respectively. All three-membered rings prepared prior to 1967 were included in a comprehensive review . 

Sheremetev and co-workers employed diazo compounds of type 60, prepared from the corresponding amines in moderate yields as alternative excellent precursors for the preparation of side-chain-functionalized derivatives (Scheme 29). Several furazans bearing reactive groups or cyclopropyl or five-membered heterocyclic substituents have been prepared by standard procedures (99MI6). 

TABLE III. Alkynylpyrazoles Prepared by Cyclization of Alkynes with Diazo Compounds [68CB3700 68LA113 88JOM247 91ZOB2286]. 

In the discussion on the structure of the aliphatic diazo compounds, the question of the existence of isomeric diazo compounds with three-membered rings was never considered. It wms therefore a surprise when the cyclic diazo compounds, i.e. the diazirines, became known their preparation wms published independently by Paulsen and by Schmitz and Ohme. ... 

The diazirines are of special interest because of their isomerism with the aliphatic diazo compounds. The diazirines show considerable differences in their properties from the aliphatic diazo compounds, except in their explosive nature. The compounds 3-methyl-3-ethyl-diazirine and 3,3-diethyldiazirine prepared by Paulsen detonated on shock and on heating. Small quantities of 3,3-pentamethylenediazirine (68) can be distilled at normal pressures (bp 109°C). On overheating, explosion followed. 3-n-Propyldiazirine exploded on attempts to distil it a little above room temperature. 3-Methyldiazirine is stable as a gas, but on attempting to condense ca. 100 mg for vapor pressure measurements, it detonated with complete destruction of the apparatus." Diazirine (67) decomposed at once when a sample which had been condensed in dry ice was taken out of the cold trap. Work with the lower molecular weight diazirines in condensed phases should therefore be avoided. 

In contrast to the aliphatic diazo compounds, which are invariably colored, all the diazirines so far prepared are colorless. The UV absorption of diazirines corresponds approximately to that of the aliphatic azo compounds. Diazirine shows in methanol an absorption maximum at 321 mja. The IR spectrum of the diazirines shows a band at ca. 1580 cm". ... 

The proof of the three-membered structure of the diazirines concludes the discussion on the three-membered ring structure of the aliphatic diazo compounds. The knowm linear aliphatic diazo compounds and the newly prepared cyclic diazo compounds (diazirines) are two independent classes of compounds completely different in their physical and chemical properties. An interconversion of the linear and cyclic diazo compounds has not so far been possible. 

The synthesis of thiepins 14 was unsuccessful in the case of R1 = i-Pr,79 but if the substituents in the ortho positions to sulfur arc /erf-butyl, then thiepin 14 (R1 = t-Bu R2 = Me) can be isolated in 99% yield.80 Rearrangement of diazo compound 13 (R1 = t-Bu R2 = H), which does not contain the methyl group in position 4, catalyzed by dimeric ( y3-allyl)chloropalladium gives, however, the corresponding e.w-methylene compound. The thiepin 14 (R1 = t-Bu, R2 = H) can be obtained in low yield (13 %) by treatment of the diazo compound with anhydrous hydrogen chloride in diethyl ether at — 20 C.13 In contrast, the ethyl thiepin-3,5-or -4,5-dicarboxylates can be prepared by the palladium catalysis method in satisfying yields.81... 

Pyrimido[5, 4 4,5]pyrazolo[3,2-c][l,2,4]triazine derivatives 1049and 1050 were prepared by treatment of diazo compound 1048, prepared from 1047, with pentane-2,4-dione and ethyl acetoacetate, respectively [92JCS(Pl)239]. 

The fact that practically all aromatic amines are readily converted into diazo compounds contributed greatly to Griess s success. The original method (Griess, 1858) by which he diazotized picramic acid (1.1 see Scheme 1-1) consisted of passing nitrous gases, prepared by the reduction of nitric acid with starch or arsenious acid, into an alcoholic solution of the amine. 

In the 1980 s three monographs were published that cover parts of the present book, namely Quinone Diazides, by Ershov, Nikiforov, and de Jonge (1981), Aromatic Diazo Compounds, by Saunders and Allen (1985), and Williams Nitrosa-tion (1988). The book of Saunders and Allen which is actually the third edition of Saunders original book (1936, 1949), focuses on synthesis and preparative methods. The other two books emphasize rather the mechanistic and physical organic aspects of their subjects. 

Methods for the Preparation of Aromatic and Heteroaromatic Diazo Compounds... 

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