Diimides isomers

The ultimate fate of diimide is sealed by its capacity to function both as a hydrogen acceptor and a powerful hydrogen donor. This latter property allows for the concerted, pericyclic hydrogen transfer from the c -diimide isomer, a less stable isomer in solution, as presented in Scheme 16.12. 

Dia ene deductions. Olefins, acetylenes, and azo-compounds are reduced by hydrazine in the presence of an oxidizing agent. Stereochemical studies of alkene and alkyne reductions suggest that hydrazine is partially oxidized to the transient diazene [3618-05-1] (diimide, diimine) (9) and that the cis-isomer of diazene is the actual hydrogenating agent, acting by a concerted attack on the unsaturated bond ... 

Protonation of the anion [SN2] by acetic acid in diethyl ether produces the thermally unstable sulfur diimide S(NH)2. Like all sulfur diimides, the parent compound S(NH)2 can exist as three isomers (Scheme 5.5). Ab initio molecular orbital calculations indicate that the (cis,cis) configuration is somewhat more stable than the (cis,trans) isomer, while the (trans,trans) isomer is expected to possess considerably higher energy. The alternative syn,anti or E,Z nomenclatures may also be used to describe these isomers. The structures of organic derivatives S(NR)2 (R = alkyl, aryl) are discussed in Section 10.4.2. 

The formal replacement of a sulfur atom in cyclo-S generates S7NH (6.1), the first member of a series of cyclic sulfur imides that includes the three diimides 1,3-, 1,4-, and 1,5-S6(NH)2 (6.2-6.4), two triimides 1,3,5-and 1,3,6-S5(NH)3, and S4N4H4 (6.5). Isomers of these ring systems containing adjacent NH groups are not known. 

Three different conformations are possible for monomeric chalcogen diimides (Eig. 10.1). Variable-temperature NMR spectra indicate that the cis,trans isomer of S(NR)2 is most stable in solution for small organic groups (R = Me, Bu). With bulkier organic substituents, small amounts of the trans,trans isomer exist in equilibrium with the cis,cis isomer. " The cis,cis isomer is observed in solutions of certain sulfur diimides with... 

The geometries and relative energies of the different conformations of model chalcogen diimides E(NR)2 (E = S, Se R = H, Me, Bu and SiMe3) have been investigated by using ab initio and DET molecular orbital methods.The cis,trans conformation is predicted to be most stable with the exception of the parent molecules E(NH)2 and the unsymmetrical systems RNSNH, for which the cis,cis conformation is slightly more stable than the cis, trans isomer. 

Chlorins, e.g. 14, form adducts with osmium(VIII) oxide, which can be hydrolyzed in aqueous sodium sulfide to bacteriochlorindiols, e g. 2, or isobacteriochlorindiols, e.g. 3. Thus, similar to diimide reductions of chlorins, metal-free tetraphenylchlorin 14 (M = 2H) is selectively oxidized to a corresponding bacteriochlorin 2 whereas the zinc chlorin gives an isobac-teriochlorin 3 on oxidation with osmium(VIII) oxide.40 With less symmetrical chlorins, very complex mixtures of constitutional isomers and stereoisomers are formed by /i-bishydroxyla-tion.17... 

Perylenes (70) are diimides of perylene-3,4,9,10-tetracarboxylic acid, and may be prepared by reaction of the bis-anhydride of this acid, 89 (1 mol) with the appropriate amine (2 mol) in a high-boiling solvent as illustrated in Scheme 4.11. The synthesis of perinones 71 and 72 involves condensation of naphthalene-1,4,5,8-tetracarboxylic acid with benzene-1,2-diamine in refluxing acetic acid. This affords a mixture of the two isomers, which may be separated by a variety of methods, generally involving their differential solubility in acids and alkalis. 

Again, the bicyclic valence isomer coexists in sufficient concentration, that the bicyclic peroxide 19 was readily accessible in ca. 20% yield. Alternatively, the thermally labile bicyclic valence isomer of cyclooctatetraene, namely bicyclo[4.2.0]-octa-2,4,7-triene, was converted into the corresponding endoperoxide on low temperature singlet oxygenation and reduced with diimide to yield 19. 

Diimide has three isomers cis- and fraws-diimide as well as 1,1-diimide (aminonitrene) (Figure l)77-80. Although fraws-diimide is the only isolated and characterized diimide, cw-diimide must be formed as a reactive intermediate in the reduction system72,77. 

The use of diimide provides a particularly convenient and general method for the selective reduction of trans double bonds of medium ring systems. The aVcyclododecene produced in this selective reduction is thermodynamically less stable than the corresponding [Pg.18]

The 1,2,3,4-isomer is also the major product if other reduction reagents [7] such as anhydrous hydrazine [6], diimide [3] or palladium hydride wrapped in gold foil [15] are used. Contrary to this result, reduction with wet Zn/Cu couple (Section 5.2.2) does not lead to the cis-l-adduct. Instead the e-isomer and the trans-3-isomer are formed as major products [5]. 

Particularly in the older literature, a and j3 designations are found. While, in many cases, this designation may simply indicate that the authors isolated two isomeric azoxy compounds of unspecified structure, where the identity of the isomers has been established the a term implies that the NO group is directly attached to the parent radical in the name, i.e., [Pg.429]

In another system recently proposed, the trans isomer of dimeric 1-chloro-2-nitrosocyclohexane would be called Dms-2,2 -dichloro-rra .y-azodioxy-cyclohexane [15,16]. In line with a system used in naming azoxy compounds, the dimers may also be named as diimide dioxides. 

The favored formation of a nucleoside 3 -(alkyl phosphate) was observed on treating the diphenyl phosphate anhydride of uridine 2, 3 -cyclic phosphate with benzyl alcohol.273 In a somewhat related reaction, on treatment with dicyclohexylcarbodiimide in aqueous pyridine, adenosine 2 (3 )-phosphate gave, initially, the 2, 3 -cyclic phosphate, which, on further reaction with the diimide, gave a mixture of the N-phosphonourea nucleoside 44 and its 2 -isomer, in unequal amounts.269 This type of reaction does not seem to occur with... 

Azoxyleiie Azoaimefhyl benzene or Tefra-methylazobenzene (called Bis-[dimethyl-phenyll-diimid Tetrameth.yl. zobenzoJ or Azoxylol in Get), (HjC)a-CsHj-N N-C6Ha--(CHj)a, mw 238.32, N 11.76%. Five isomers are listed in the literature 4,4 -azo-o-xyIene or 3,4,3 4 -Tetramethyl-azobenzene (Ref 1) 4,4 -azo-m-xylene or Z S -tetramethyl-azobenzene (Ref 2) 4,5 azo-m-xylene or... 

It was found that most synthetic processes that are employed to prepare the diimide reagent generate trans-diimide, but ds-diimide undergoes faster hydrogen atom transfer to a double bond than does the trans isomer. It follows that a fast trans-cis isomerization precedes reduction. The transfer of hydrogen atoms takes place in a synchronous process188 via the transition state 19 ... 

The effect of polar groups on the diimide reaction is sensitive to the configuration of the attached groups. For example, fumaric acid (trans) is ten times as reactive as maleic acid (els ) and the ratio of reactivities of the geometrical isomers of cinnamic acid, trans/cis. is 10 3 (ref. 21b). In comparison, cis- and trans-2-butene have almost identical reactivities. The difference may be explained by a change in the degree of advancement of the transition state towards the saturated product where the eclipsed conformation would result in a greater non-bonded repulsive interaction between the cis-substituents than the trans. 

Benzeneazonapbtbalene(called Phenyl a-naphthyl -diimid 1-Benzolazo-naphthalin or Benzol-azo--naphthalin in Ger), C6HS,N N.C10H7 mw 232.27, N 12.06%, is described in Beil 16,78 Mononitrobenzeneazonaphthalene, 02N.CgH4.N -N.C10H7 mw 277.27, N 15.16%. The [3-Nirro-benzene - azo-a-naphthalene, isomer is described in Beil 16,78 Dinitrobenzeneazonapbthalene,... 

Bats, 54 Batteries, 54 Benzene isomers, 55 Benzyl compounds, 55 Bis(arenediazo) oxides, 56 Bis(arenediazo) sulfides, 56 Bis(difluoroamino)alkyl nitrates, 56 Bis(fluorooxy)perhaloafkanes, 57 Bis(sulfur)diimides, 57 Bitumen, 57 Bleaching powder, 57 Bleve, 58... 

Fig. 9.4 (a) 3He NMR spectrum for a reaction mixture of 3He C60H2 produced from hydrobora-tion of 3He C60. (b) 3He NMR spectrum from diimide reduction of 3He C60 showing a signal from 3He C60H2 as well as from several different isomers of 3He C60H4 (Cross et al. 1996)... 

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