Diazo compounds, aliphatic preparation

Diazo compounds, aliphatic, preparation, 15, 3, 62 Diazofluorene, 15, 63 Diazomethane, 15, 3 Diazotization... 

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. 

If an aliphatic amino group is to a COOR, CN, CHO, COR, and so on, and has an a hydrogen, treatment with nitrous acid gives not a diazonium salt, but a diazo compound Such diazo compounds can also be prepared, often more conveniently, by treatment of the substrate with isoamyl nitrite and a small amount of acid. Certain heterocyclic amines also give diazo compounds rather than diazonium salts. ... 

There are many preparations of diazonium salts listed in Organic Syntheses, but they are always prepared for use in other reactions. We do not list them here, but under reactions in which they are used. The preparation of aliphatic diazo compounds can be found in OS III, 392 IV, 424. See also OS VI, 840. 

These authors also prepared novel epoxy-bridged cyclooxaalkanones in this process, the carbonyl group always acts as 1,3-dipolarophile, even if one employs ct,(3-unsaturated aldehydes. Thus, reaction of 6/2-16 with aliphatic or aromatic aldehydes 6/2-17 in the presence of catalytic amounts of rhodium acetate gave 6/2-18, regioselectively. With the a, 3-unsaturated aldehydes 6/2-20, only cycloadducts 6/2-21 were obtained using the diazo compound 6/2-19 as substrate (Scheme 6/2.3) [191]. 

Diazomethane, the simplest aliphatic diazo-compound, was first prepared by von Pechmann1 in the following way ... 

The aliphatic diazo-compounds can also be prepared by careful dehydrogenation of the hydrazones (with HgO) (Curtius, Staudinger) and, conversely, they are converted into the latter by hydrogenation ... 

The history of cycloaddition chemistry using aliphatic diazo compounds began in the 1890s when Buchner (1) and von Pechmann (2) reported that ethyl diazoacetate and diazomethane underwent cycloaddition across carbon-carbon multiple bonds. Ever since that time, diazo compounds have occupied a major place in [3 +2]-cycloaddition chemistry (3,4). For a long time, diazo compounds, as well as organic azides, have been one of the more synthetically useful classes of 1,3-dipoles. No doubt this was because many different mono- and disubstituted diazo compounds could be prepared (Scheme 8.1) and isolated in pure form, in contrast to other 1,3-dipoles that are typically generated as transient species. 

Numerous methods to prepare individual classes of aliphatic diazo compounds have been extensively developed. The major strategies for their synthesis involve the alkaline cleavage of N-alkyl-N-nitroso-ureas, -carboxamides and -sulfonamides, dehydrogenation of hydrazones, as well as diazo group transfer from sulfonyl and related azides to active methylene compounds, and electrophilic diazoalkane substitution reactions. These synthetic methods have been comprehensively reviewed (15,16). Useful information on the preparation of selected diazo compounds can be found elsewhere (6,17). 

An interesting preparation of aliphatic diazoalkanes (R R C = N2 R, R = alkyl) involves the photolysis of 2-alkoxy-2,5-dihydro-1,3.4-oxadiazoles (see Scheme 8.49). When the photolysis is carried out in the presence of an appropriate dipolarophUe, the diazo compounds can be intercepted (prior to their further photolysis) by a [3 + 2] cycloaddition reaction (54). As an example, 2-diazopropane was intercepted with A-phenylmaleimide (54) and norbornenes (55) to give the corresponding A -pyrazolines. 

In contrast to the epoxides, preparative routes to the aziridines are fairly evenly split between the [C=N + C] and the [C=C + N] routes. Among contributions in the former category, aziridine carboxylate derivatives 110 can be prepared through the lanthanide-catalyzed reaction of imines with diazo compounds, such as ethyl diazoacetate (EDA). In this protocol, iV-benzyl aryl aldimines and imines derived from aromatic amines and hindered aliphatic aldehydes are appropriate substrates <99T12929>. An intramolecular variant of this reaction (e.g.. Ill —> 112) has also been reported <990L667>. 

Monocyclic 1,3-oxazepines (325) with aryl substituents at the 2-, 4- and 7-positions can be prepared in moderate yield (20-40%) by the reaction of aliphatic diazo compounds with 1,3-oxazinium perchlorates (324) (74S187). Tetra- and penta-phenyl-l,3-oxazepines (328 R = H or Ph) have been obtained via the reaction of azide with pyrylium salts (326) (78H(l 1)331). This principle had earlier been applied to the preparation of 1,3-benzoxazepines (74CR(C)(278)1389> and more recently to 3,1-benzoxazepines (81JHC847). The preparation of 2-phenyl-1,3-oxazepine.(331) by the UV irradiation of (329) is mechanistically interesting in that it apparently involves an intermediate (330) of the same type as (327) (73TL1835), but the method has only been used in this one case. One of the few examples of a dihydro-1,3-oxazepine (333) has been prepared by the thermolysis of the aziridine (332) (68JOC4547). 

The explosive properties of the potassium salt of nitrocyanamide first attracted McKay s [37] attention. He separated this potassium salt as a by-product from the preparation of aliphatic diazo compounds by the hydrolysis of N-alkyl-N-nitroso-N -nitroguanidines with an aqueous solution of sodium hydroxide at temperatures from 0°C to room temperature ... 

Monocyclic 1,3-oxazepines (290) can be prepared by reaction of aliphatic diazo compounds with... 

Ketone hydrazones can be converted into aliphatic diazo compounds which are, in contrast to nonfluorinated analogs, quite stable at room temperature. 2-Diazo-l,l,1-trifluoropropane is obtained as a solution in diethyl ether or pentane by the oxidation of l,l,l-trifluoropropan-2-one hydrazone using silver oxide.243 Analogously, phenyl trifluoromethyl ketone hydrazone is oxidized to the diazo compound 6 by mercury(II) oxide in alkaline media.362 Bis(per-fluoromethyl)- 7 and bis(perfluoroethyl)diazomethane are prepared by lead(IV) acetate oxidation of the corresponding hydrazones in benzonitrile solution at 0-25 c.244,245... 

Monocyclic 1,3-oxazepines 419 can be prepared by reaction of aliphatic diazo compounds with 1,3-oxazinium perchlorates 418 (Scheme 194) <1974S187>. Tetra- and penta-phenyl-1,3-oxazepines 421 (R = H or Ph) have been obtained by the reaction of azide ion with pyrylium salts 420 (Scheme 195) <1978H(11)331>. 

Adamson DW, Kenner J (1937) Improved preparation of aliphatic diazo-compounds, and certain of their properties. J Chem Soc 1551-1556 Beynon JH, Saunders RA, Williams AE (1968) The mass spectra of organic molecules. Elsevier, Amsterdam, 352-394... 

Aliphatic diazo compounds bearing electron withdrawing groups are moderately stable and can be easily prepared from readily available precursors. Photolysis of these diazo compounds or thermolysis in the presence of a metal salt (Cu, Rh reaction are among the most widely applicable protocols of cyclopropanations. 

A few examples of the reduction of aliphatic diazo compounds to hydrazines exist," but this is not a generally applicable method for the synthesis of alkylhydrazines. On the other hand, arylhydrazines can be prepared by reduction of aromatic diazonium salts.The most commonly used reagents for this conversion are sulfur dioxide (or sodium sulfite) and tin(II) chloride, these being used to reduce arenediazo-nium chlorides in aqueous solution. Several other reagents, including sodium amalgam and triphenylphosphine, have been used for specific reductions of this type. Arenediazonium tetrafluoro-borates have been reduced to the correspwnding hydrazinium salts (3) by benzeneselenol in dichloro-... 

Peter Griess, 1858.—Diazo compounds were discovered and first prepared by Peter Griess in 1858. The historical method used by him is the same in general as is now used widely in dyestuff manufacture. It has already been described and consists in the action of nitrous acid on an aromatic primary amine, e.g., aniline. When this reaction takes place, at ordinary or slightly raised temperatures, the same products are obtained as with aliphatic primary amines, viz., the hydroxyl compound of the hydrocarbon radical, free nitrogen and water. 

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