Nitrogen, extrusion

Bicyclic derivatives Rate constants for nitrogen extrusion 78JA5122... 

Increased sensitivity towards acid is observed when protonation occurs on a functional group outside the diazirine ring, giving rise to electron dilution at the carbon atom adjacent to the diazirine carbon. The products isolated are in accord with the proposal (79AHC(24)63) that cation formation at this carbon atom leads to nitrogen extrusion, probably with formation of a vinyl cation. Thus protonated hydroxydiazirine (209) yields acetone, and methylvinyldiazirine (199) on treatment with acids yields butanone (67CB2093). 

Hydroxymethylmethyldiazirine (209 unprotonated) formed propionaldehyde as the sole product by thermal nitrogen extrusion 4-hydroxy-l,2-diazaspiro[2.5]oct-l-ene (218) formed a mixture of cyclohexanone (73%), cyclohexenol (21%) and cyclohexene oxide (5%). Thermal decomposition of difluorodiazirine (219) was investigated intensively. In this case there is no intramolecular stabilization possible. On heating for three hours to 165-180 °C hexafluorocyclopropane and tetrafluoroethylene were formed together with perfluorofor-maldazine 64JHC59). 

Photolysis of dlazirines to nitrogen and carbenes is a general reaction and plays a greater role in carbene chemistry than photolysis of linear diazo compounds. Whereas the latter are often obtained only under the conditions of their thermal decomposition from suitable precursors, diazirines are obtainable in a pure state in most cases. Photolysis has the further advantage to permit nitrogen extrusion at atmospheric pressure, even with low-boiling materials. 

A novel principle of diaziridine synthesis was found in nitrogen extrusion from tetrazolines (275). Af-Aryldiaziridines (276) almost unaccessible by older procedures thus become available (74CL185). 

Photolytic nitrogen extrusion from tetrazoline derivatives (283) and (284) permits further syntheses of diaziridin-ones (285a) and -imines (285b) respectively (75AG(E)428). Thermal carbon dioxide extrusion from a five-membered precursor can also give a diaziridinimine (75JOC3112). 

Diazirine, fluoromethoxy-nitrogen extrusion, 7, 224 Diazirine, methylvinyl-rearrangement, 7, 221 Diazirines addition reactions to Grignard compounds, 7, 2 0 as carbene precursors, 7, 236 IR spectra, 7, 203 microwave spectrum, 7, 199 molecular spectra, 7, 202-204 nitrogen extrusion, 7, 223 NMR, 7, 202 photoconversion to diazoalkanes, 7, 234 photoisomerization, 7, 221 photolysis, 7, 225-227 quantum chemical investigations, 7, 197 reactions... 

The reaction of oxepin with dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate affords a 2 1 mixture of products 9 a and 10, whose formation can be rationalized by a [4+2] and a [4 + 6] cycloaddition, followed by nitrogen extrusion.235 With 2,7-dimethyloxepin, only dimethyl 6,8-dime-thy 1-2.4a-dihydrooxepino[4,5-c/]pyridazine-l,4-dicarboxy late (9b) as product of the [4 + 2] cycloaddition can be isolated.235 236... 

Open-chain and cyclic compounds containing azo groups (-N2 —), such as azoalkanes, azoarenes, pyrazolines, triazolines, etc. may also eliminate N2, but these reactions are called azo-extrusions (IUPAC, 1989 a). The terms denitrogenation and nitrogen extrusion, both used by Adam et al. (1992, 1993) and by Adam and Sengelbach (1993) should not be used. They are superfluous and ambiguous. 

The free-radical reaction may be equally initiated by photoactivated sulfur dioxide (3S02)442 (equation 79). On the other hand, polysulfones are obtained by radical copolymerization of appropriate olefins with sulfur dioxide443-449, and similarly, uptake of sulfur dioxide by a radical-pair formed by nitrogen extrusion from an azo compound yields the corresponding sulfone450 (equation 80). Correspondingly, alkylbenzenes, dibenzoyl peroxide, and sulfur dioxide yield sulfones under thermal conditions451... 

Formal 1,3-dipolar addition of a diazoalkane to an unsaturated metal fragment ML would produce 53. Such a species would be expected to be unstable with respect to nitrogen extrusion, and would seem a plausible intermediate in the diazo reaction ... 

Tetrazine (171) and its derivatives are electron-deficient cycloaddends, which undergo [4 + 2] cycloadditions with inverse electron demand. When bicyclopropylidene (3) was added to a dichloromethane solution of 171, its red color disappeared within 1.5 h at room temperature. The white crystalline product isolated in 86% yield turned out to be a mixture of at least two stereoisomeric compounds 174, trimers of the 8,9-diazadispiro[2.0.2.4]deca-7,9-diene (173) evidently formed via the normal [4 + 2]-cycloadduct 172 after nitrogen extrusion (Scheme 25) [13b]. 

Vinylcarbenes. The use of diazoalkenes as vinylcarbene precursors is often precluded by rapid cyclization, with formation of pyrazoles. However, on photochemical generation of the diazoalkenes in situ, cyclization and nitrogen extrusion can proceed competitively. Photolysis of 1,3-diphenylpropenone to-sylhydrazone sodium salt (5) in MeOD afforded 3,5-diphenylpyrazole (9) and l,3-diphenyl-3-methoxypropene (10) in similar amounts.17 If 10 is formed by way of the 1,3-diphenylallyl cation (8), the deuterium should be distributed between C-l and C-3 of 10 (Scheme 6). The observed ratio of 10a to 10b was 66 34 the methoxy group is bound preferentially to the deuterated site, which originates from the divalent carbon of 7 (for a discussion of this effect, see below). 

Table 7.6 lists the theoretical BDEs of the M-L bonds in the group-10 Ni(CO)3L, Pd(CO)3L and Pt(CO)3L complexes calculated at the MP2/II and CCSD(T)/II levels of theory [49, 50], The only experimental value known for those compounds is an estimate of ca. 10 kcal/mol obtained for the (CO)3Ni-N2 bond energy at 298 K [59], This estimate is based on kinetic measurements of nitrogen extrusion from the complex. Thermal corrections to the CCSD(T)/II value of D0 = 4.6 kcal/mol yield a theoretical prediction of 6.7 kcal/mol, which is in a reasonable agreement with experiment [49]. The MP2/II BDEs listed in... 

A ring contraction can be obtained by heteroatom (sulfur, nitrogen) extrusion from... 

As early as 1919 Staudinger and Meyer reported for the first time the synthesis of an iminophosphorane (3) from triphenylphosphane (2) and organic azides (1) with simultaneous nitrogen extrusion (Scheme 1) (19HCA635). A modern graphic representation of the first Staudinger iminophosphorane is shown in Fig. 1. A facsimile of the original paper published in Helvetica Chimica Acta is shown in Fig. 2. 

Kinetic studies showed the rate of nitrogen elimination from compound 4a (Scheme 4) is first order and correlates with the Y value of the solvent (79JOC1717). A slower rate of decomposition was observed in more polar media. This would seem to reflect a greater solvation of starting material, which retards the nitrogen-extrusion process in more polar media. If the intermediate is better represented by 12 rather than 13, nitrogen elimina-... 

An extension of this route has been developed by Diirr et al. It consists in the irradiation of 3//-spiropyrazoles 74 which rearrange to 3//-indazoles 75 prior to nitrogen extrusion and biradical cyclization to cycloproparenes 76. As above, only 1,1 -disubstituted cycloproparenes (mainly with alkoxycarbony 1 groups) are acces-... 

The synthesis of li7-cyclopropa[/]phenanthrene (142) presented unexpected difficulties and met many failures. Early approaches used a variety of schemes which were not adequate for this highly reactive compound and invariably produced ring-opened products. Thus irradiation of the substituted indazole 138 resulted in nitrogen extrusion and formation of the biradical 139, which reacted with the solvent, benzene, to form 140. The desired cycloproparene 141 was not formed. Ring contraction of 144, in turn, produced derivatives of 9-phenanthroic acid, the formation of which was shown not to involve phenanthrocyclopropenone (143). °° The attempted 1/3/elimination of 145 was similarly unsuccessful and afforded no 142. ... 

Dialkyl-l,2,4-oxadithiolane-2-5 -oxides (160) have been synthesized from the dihydro thia-diazole (161) via nitrogen extrusion and 1,3-dipolar cycloaddition of the intermediate ylide with sulfur dioxide (Scheme 45) <90BSB265>. The formation and trapping of carbonyl oxides is described... 

A -Oxatriazoline (60), formed as shown in Scheme 15, is reported to undergo a facile nitrogen extrusion reaction with formation of a nitrone (61) <76BCJ3173>. 

Vogel and Delavier (26) reported a synthesis of the 6-azabicyclo[3.2.2]nonane skeleton 130 using an intramolecular azide-alkene cycloaddition strategy (Scheme 9.26). When refluxed in xylene, the azide 126 underwent an intramolecular 1,3-dipolar cycloaddition with the internal alkene. Nitrogen extrusion and subsequent rearrangement led to a mixmre of compounds 128, 129, and 130. Reactions of azides with the double bond of dienes were also used in various total syntheses of alkaloids, and will be discussed later in Section 9.2.2. 

Nitrogen extrusion from tetraazaphenanthrolines is a well-known and useful route to diazabiphenylenes, and several methods were reported in <1996CHEC-II(7)921>. This route has, however, only been reported for the diazabiphenylenes and not the tri- or tetraaza analogues. Extrusion of SO2 from dipyridothiophene dioxides is also possible <1996CHEC-II(7)921>. The 1,5- and 1,7- diazabiphenylenes are unknown. 

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