Diimine intermediate

Substituted succinonitriles give 3-substituted pyrroles on reduction with DIBAL-H (84TL1659) via diimine intermediates which undergo cyclization and aromatization (Scheme 39). This reaction was used in the synthesis of unusual pyrroles (e.g. 119) which were used to prepare sterically shielded porphyrins (94AG(E)889). 

Chemical and electrochemical oxidation of these [Pt Me2(a-diimine)] species in MeCN was later studied in more detail in the Tdset group (38). Irreversible electrochemical waves were again observed, and bulk electrolysis revealed consumption of 1.1-1.6 FmoP indicative of a le oxidation process. (Electro)chemical bulk oxidation leads to only marginal formation of methane or ethane, and almost quantitative formation of the species [Pt Me3(a-diimine)(NCMe)] and [Pt Me(a-diimine)(NCMe)] in a 1 1 ratio. It was proposed that the short-lived [Pt Me2(a-diimine)] " " decomposes via a bimolecular methyl transfer from one platinum to another. This explains the product distribution and the lack of products derived from free alkyl radicals. This could either involve a reaction between two [Pt °Me2(a-diimine)] + intermediates or a reaction of [Pt° Me2(a-diimine)] + with the starting material [Pt Me2 (a-diimine)]. 

Kidwai et al. [100] reported the synthesis of 2,4,5-triaiylimidazoles 68 in excellent yields via the condensation of benzoin, ammonium aeetate, and aromatic aldehydes using elemental iodine as an efficient eatalyst Moleeular was capable of binding with the carbonyl oxygen atom and increased the reactivity of the parent carbonyl compound. Iodine facilitates the formation of the diimine intermediate, which under mild catalysis of I2 was condensed further with the eaibonyl carbon of the 1,2-diketone followed by dehydration to afford the iso-irrridazole, which was rearranged via a [1,5] sigmatropic shift to the reqrrired 2,4,5-triarylimidazole derivatives (Scheme 10.50). 

The authors then investigated the chiral vicinal diamine directly in the Michael addition for the synthesis of warfarin (Table 9.13). Importantly, the authors postulated that the diimine intermediate was an essential element for the high degree of asymmetric induction and concluded that the size of the... 

In the electrochemical oxidation, 2,6-diamino-8-purinol (II) is further oxidized in a 2e, 2H+ reaction to an unstable product which was proposed to be a diimine (III). This product has not been identified directly, but its formation is strongly supported by the identification of a diol (VI, Fig. 1) which must form through hydrolysis of the diimine intermediate (III VI, Fig. 1). The diol decomposes to the final product which was identified as the bicyclic carboxylic acid (IX, Fig. IB). In the identification, separations were used to isolate intermediates and products, and their chemical identity was confirmed by gas chromatography/ mass spectrometry. Volatile derivatives were formed before GC/MS analysis. The off-line measurements have drawbacks associated with necessary manipulation of samples i. ... 

Oxidation H ir Colorant. Color-forming reactions are accompHshed by primary intermediates, secondary intermediates, and oxidants. Primary intermediates include the so-called para dyes, -phenylenediamine, -toluenediamine, -aminodiphenylamine, and p- am in oph en o1, which form a quinone monoimine or diimine upon oxidation. The secondary intermediates, also known as couplers or modifiers, couple with the quinone imines to produce dyes. Secondary intermediates include y -diamines, y -aminophenols, polyhydroxyphenols, and naphthols. Some of the more important oxidation dye colors are given in Figure 1. An extensive listing is available (24,28). 

Dye formation is complex because shading is achieved by employing several developers and several couplers in the same dye bath. The process is illustrated by -phenylenediamine, which is oxidized by the peroxide to a quinone diimine. This short-Hved intermediate can react, for example, with resorcinol to yield a brownish indoaniline. Table 17 provides some insight into the many interactions that exist from just a few components. Further shading is possible by including semipermanent colorants (see Table 16), especially nitroaniline derivatives. 

The synthesis of metal-eoordinated 1-azirines and the reaetions of azirines indueed by metals have opened a new area in the ehemistry of this small ring heteroeyele. Many of the reaetions eneountered bear resemblanee to previously diseussed thermally and photo-ehemieally indueed reaetions of 1-azirines. The reaetion of a series of diiron enneaearbonyls in benzene results in eoupling and insertion to give diimine eomplexes and ureadiiron eomplexes as well as pyrroles and ketones (76CC191). A meehanism for the formation of these produets whieh involves initial 1,3-bond eleavage and generation of a nitrene-iron earbonyl eomplex as an intermediate was proposed. 

Singlet phenylnitrene, and hence /V,A -diethyl-3//-azcpin-2-amines, e. g. 102, can be generated by the thermolysis of A,-phenyl-Af,<9-bis(trimcthylsi]yl)hydroxylamine (100) in the presence of dialkylamines the reaction fails, however, with arylamines.210 Photofragmentation of the spiro oxaziridine 101 in diethylamine solution also produces the 3//-azepine 102,2,1 and an oxaziridine intermediate is probably involved in the formation, in low yield (1 %), of azepine 102 by the photolysis of A/,A( -diarylbenzoquinonc diimine A/,A/ -dioxides in benzene/die-thylamine solution.212... 

M -Dialkyldiazacrown ethers and their precursors fcis(alkylamino) derivatives of tri- and tetraethylene glycols were prepared <96CCCC622>. New hydroxy-bearing dibenzo-azocrown ethers have been conveniently prepared utilizing l,3-Ws(2-formylphenoxy)-2-propanol and a diamine, followed by reduction of the intermediate diimine <96P1197>. Fluorescent photoinduced electron transfer sensor 5 with monoaza-18-crown-6 and guanidinium receptor units demonstrated a fluorescence with T -aminobutyric acid in a mixed... 

An NMR and structural study characterized the intermediates generated from diimine catalysts on reaction with diazodiphenylmethane.193 The dominant species in solution is dinuclear, but a monomeric metallocarbene species can be detected. 

Five-membered heteroaromatic N-oxides have been less systematically investigated although in most cases reaction via an intermediate oxaziridine appears to be involved. The imidazole 3-oxide 90, for example, is converted on irradiation in polar or nonpolar media to the diimine 91.7 5... 

In early studies, reaction of the Ni(n) complexes (59) and (60) of the trans and cis (diimine) isomers of the Curtis macrocycle with nitric acid yielded the tetraimine species (294) and (295), respectively. There is strong evidence that these reactions proceed via Ni(m) intermediates... 

One of the most defining characteristics of the late metal a-diimine polymerization systems is the uniquely branched polyolefins that they afford. This arises from facile p-hydride elimination that late transition metal alkyl complexes undergo. The characteristics of the isomerization process have been the subject of much investigation, particularly with the more easily studied Pd(II) a-diimine system. The process is initiated by P-hydride elimination from the unsaturated alkyl agostic complex 1.17, followed by hydride reinsertion into olefin hydride intermediate 1.18 in a non-regioselective manner (Scheme 5). In doing so, the metal center may migrate... 

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