Elimination of Nitrogen from Diazo-compounds

Photolysis of (2-phenoxyphenyl)phenyldiazomethane (36) in cyclohexane at 10°C gave phenylcycloheptabenzofuran (37) via (2-phenoxyphenyl)phenylcarbene.The infrared spectrum of photo-chemically generated anthranylidene has been determined,and the dicarbene, (9,lO-dihydro-9,lO-o-benzeno-2,6-anthrylene)di(phenyl-methylene), has been shown by e.s.r. spectroscopy to have a quintet ground state.Products of photodecomposition 1,l-dimethyl-2-diazo-2-phenylethanol (38) in cyclohexane are the hydroxy ketone (39), the oxirane (40) and 3-phenylbutan-2-one (41), whereas reaction in methanol gave the methoxy alcohol (42) and the alkene (43).43 

The photoreactions of bis-diazo ketones have also been examined. Irradiation of l,3-bis(diazo)-2-indanone (52) in an argon matrix at 10 K gave, not unexpectedly, the diazo ketone (53) this was converted on further irradiation into highly strained compounds to which the carbonyl structures (54) and (55) were provisionally assigned. l,2,3-Butatriene-l,4-dione, C4O2, is formed, also in an argon matrix, on photodecomposition of either of the bis(diazo)triketones (56) or (57).  

2-Quinonediazides, which are of commercial value as photoresists, undergo analogous ring contraction on photochemically induced elimination of nitrogen. 

The synthesis and use of diazo compounds as photoaffinity probes has again been widely reported. 

Loss of nitrogen has also been observed on irradiation of diazonium salts. The quantum yields for the photodecomposition of stilbene- and coumarin-diazonium tetrafluoroborates and for stilbenediazonlum tetrafluoroborate ion pairs have been 

Photoelimination of nitrogen from diazo-compounds is a simple and versatile process for the generation of carbenes. The diazoadamantane (65) is a surprisingly stable compound which on irradiation yields the hydrocarbon (66), the azine (67), and the alcohol (68) via the carbene. The origin of the oxygen atom 

1-oxides (69), on irradiation in benzene or methanol, are converted into the 

2-acylpyridines (70).40 Alternative mechanisms have been considered for this novel elimination, and although there is no direct evidence for the formation of a free carbene, such a species may well be involved. 

Spectroscopic evidence for the carbene cyclopentadienylidene (71) has been observed in the photodecomposition of diazocyclopentadiene (72) in a low-temperature matrix.41 Dimerization of the carbene to afford fulvalene (73) occurs 

The photoelimination of nitrogen from diazoketones and the fate of the resulting species are still subjects of major interest. A successful photochemically induced Wolff rearrangement of an acyclic /Sy-unsaturated diazo-ketone in aqueous dioxan has been reported.60 In the photodecomposition of the diazo-ketone 

The photoelimination of nitrogen from diazo-compounds provides a 

Aryl and diarylcarbenes are easily prepared by irradiation of the corresponding diazo-compounds. Topics studied include the 

Arylcarbenes generated in this fashion react with a wide variety of reagents. Both singlet and triplet diphenylcarbene 

The study of the photodecomposition of a-diazo ketones continues to attract attention. The strong and weak triplet signals observed in the e.s.r. spectrum on photolysis of crystalline azi-benzil at 77 K have been assigned to the s-Z and the s-E stereo- 

Carbene rearrangement of a different type is preferred in the (pentamethyldisilanyl-diazomethyl) ketones (70) which are converted on irradiation into 1-oxa-2-silacyclobut-3-enes (71) and 1,5-dioxa-2,6-disilacyclo-octa-3,7-dienes (72) via the unstable 3-oxa-1-silaprop-1-enes (73). 3-Diazoacetylretinals have been synthesized for use in photoaffinity labelling. 

The photoelimination of nitrogen from diazo-compounds provides a simple and versatile route for the generation of carbenes. The reactions of such carbenes are easily studied under various conditions. The relative amounts of carbene-derived products arising by 1,2-hydrogen migration, (57) and (58), and 1,2-phenyl migration, (59), on irradiation of 1,2-diphenyl-1-diazopropane (60), have been 

1-Phosphoryl-substituted 2-vinylcyclopropanes have been prepared by the addition of photochemically generated carbenes to 2,3-dimethylbutadiene. Similarly, benzophenone-sensitized photodecomposition of the dimethyl (a-diazoalkyl)phosphonates (68) in the presence of diketen (69) affords E- and Z-1-substituted l-(dimethylphosphono)-5-oxaspiro[2.3]hexanes (70) and (71). Rearrangement of the carbene (72), leading to the formation of short-lived 

Guiborel, R. Danion-Bougot. R. Danion. and R. Carrie, Tetrahedron Lett., 1981, 22, 441. 

The study of the mechanism and synthetic applications of photodecomposition of diazoketones has continued to attract attention. There is already much indirect evidence for the existence of an a-oxo-carbene interconversion on photoelimination of nitrogen. A study of unsymmetrically substituted a-diazoketones (82) and (83) has now established that not only are singlet a-oxo-carbenes (84) and 

Irradiation of the pyrazoline diazo-amide (101) in methanol affords a mixture of isomeric methyl 3-phenylazobut-2-enoates (102). Details of the precise mechanism implicated in this transformation are uncertain, but the process must presumably involve ring opening of the intermediate carbene (103). A carbene-insertion reaction is observed on irradiation of the diazo-amide (104) to give the novel j8-lactam (105).  

Carbenes are readily obtained by the photodecomposition of diazo-compounds. The reactions of carbenes generated in this way in rigid matrices at low temperatures have been reviewed. Addition of singlet methylene to acetonitrile affords the nitrile ylide 

Particular attention has been devoted to the characterization and to the reactions of aryl carbenes. Energy differences between singlet and triplet ground state carbenes are usually 

Unlike phenyldiazomethane which is converted on irradiation into cyclohepta-1,2,4,6-tetraene, the carbenes (52) generated by photodecomposition of the naphthyldiazomethanes (53) undergo rearrangement to the benzobicyclo[4,1.0]hepta-2,4,6-trienes (54). Hydrogen abstraction by triplet diphenylcarbene is observed on photodecomposition of diphenyldiazomethane in cyclohexane, whereas singlet-derived solvent insertion reactions compete with hydrogen 

A study of the effect of temperature on the photodecomposition of diphenyldiazomethane in methanol supports the previous 

Reactions of photochemically generated aryl carbenes with other species have also been studied. The mechanism of addition of carbenes to alkenes is of current interest. A non-concerted pathway with a reversible first step has been shown to be involved 

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Photo-de-diazoniation has found relatively little application in organic synthesis, as is clearly evident from the annual Specialist Periodical Reports on Photochemistry published by the Royal Society of Chemistry. Since the beginning of these reports (1970) they have contained a section on the elimination of nitrogen from diazo compounds, written since 1973 by Reid (1990). In the 1980s (including 1990), at least 90% of each report is concerned with dediazoniations of diazoalkanes and non-quinon-oid diazo ketones, the rest being mainly related to quinone diazides and only occasionally to arenediazonium salts. 

There are terms proportional to the concentration of added nucleophile in the rate equations for the elimination of nitrogen from diazo compounds (Sect. 8) and the ring-opening of epoxides (Sect. 6). However, these reactions are not examples of nucleophilic catalysis according to the more restricted definition as the nucleophiles are consumed in the overall process rather than being regenerated in a final step. 

Elimination of Nitrogen from Diazo Compounds and Diazirines... 

H-Pyr azoles readily undergo photochemically induced elimination of nitrogen to yield the corresponding cyclopropenes, often by way of detectable vinyl diazo intermediates. l-Aryl-3-methyl-2-phenyl-l-diazobut-2-enes have, in fact, been prepared in this way from the appropriate pyrazoles.345 The vinyl diazo compounds 416, obtained by irradiation of the 3//-pyrazoles 417, were further converted to cyclopropenes 418 via vinylmethylene intermediates 419 by irradiation at 10°C.346 1-Acylcyclopropenes have been... 

This is a good point to remind you of other double losses from molecules. Just as a elimination gives a carbene while p elimination gives an alkene, loss of nitrogen from a diazo compound gives a carbene but loss of nitrogen from an azo compound such as AIBN (azobisisobutyronitrile) gives two radicals (Chapter 39). 

As already mentioned, under the preparation of methyl amine, the behaviour of the aliphatic primary amines toward nitrous add is very different from that of the aromatic compounds. While the former yield alcohols with the elimination of nitrogen, the latter, in a mineral acid solution, under the influence of nitrous add, yield diazo-compounds, discovered by Peter Griess, in the form of thdr mineral add salts. 

Cinnolines may be formed by the cyclization of 2-hydrazone or 2-hydrazonophosphorane derivatives of 3-(2-fluoro- or chlorophenyl)-3-oxopropionates (Scheme 87), which are prepared from the oxopropionates via reaction with /i-toluenesulfonyl azide and treatment of the diazo derivatives with phosphines. Simple hydrazones undergo cyclization by displacement of fluoride under thermal or basic conditions, and reaction of chloro compounds is successful under basic conditions, though Wolff-Kishner reduction may compete in the absence of a methyl group on the terminal nitrogen. The diazo compounds cyclize, via tri- -butylphosphazines, more readily than do the hydrazones and base catalysis is not required it may be that cyclization proceeds via a phosphonium salt, with subsequent hydration and elimination of tri- -butylphosphine oxide. The triphenylphosphazines do not cyclize, but are labile intermediates to the hydrazones <88Cpbi321>. 

This section deals with the photochemical loss of nitrogen from compounds containing a diazo group. As a result of the scale of the work some material has had to be excluded. Within this section paths to the synthesis of diazo compounds from hydrazones have been omitted. Much of the use of diazo compounds and the photochemical (and thermal) elimination of nitrogen is in the generation of carbenes, from which a variety of reactions of synthetic value can occur. This short section is aimed mainly at that area, although some reference will be made to the elegant low-temperature studies that have been carried out. 

This reaction was first reported by Buchner and Curtius in 1885 and subsequently by Schlotterbeck in 1907. It is the reaction for forming ketones from aldehydes and aliphatic diazo compounds and is thus known as the Buchner-Curtius-Schlotterbeck reaction. This reaction has been extended to synthesize jS-keto esters from the condensation between diazo esters and aldehydes." It should be pointed out that epoxides and aldehydes are also produced in this reaction, and the preparation of keto esters can also be performed in the presence of Lewis acids or via a two-step process involving an Aldol Reaction of diazo ester and aldehyde followed by the oxidative elimination of nitrogen. ... 

Photochemical elimination reactions include all those photoinduced reactions resulting in the loss of one or more fragments from the excited molecule. Loss of carbon monoxide from type I or a-cleavage of carbonyl compounds has been previously considered in Chapter 3. Other types of photoeliminations, to be discussed here, include loss of molecular nitrogen from azo, diazo, and azido compounds, loss of nitric oxide from organic nitrites, and loss of sulfur dioxide and other miscellaneous species. 

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