1.4- Diaza-l,3-dienes

Diaza-l,3-dienes, tantalum complexes, 5, 176-177 Diaza-titanacyclopentenes, generation, 4, 419 Diazines, metallation, 9, 22-23... 

Diaza-l,3-dienes, including dimines derived from glyoxal, 2/ftimidazole derivatives, dehy-droindigo, and benzofurazan V-oxide undergo [4 4- 2] cyeloaddition reactions with alkenes,... 

Additional experiments were also carried out with complex 133 which results from the substitution of the COD ligand in 73 by a 1,4-diaza-l,3-diene (DAD) [48], The catalytic activity of 133 in the cyclodimerization of 1,3-butadiene was compared to that of its carbon counterpart the [Fe(r/6-toluene)(DAD)] complex. In this case, the toluene complex proved to be 10 times more efficient and yielded better TON than the phosphinine-based complex for the formation of COD (1,5-cyclooctadiene) and VCH (vinylcyclohexene). This lack of activity was ascribed to the stronger affinity of phosphinine ligands towards Fe(0) thus limiting the generation of the 12 VE [Fe(DAD)] complex which is the genuine catalytic active species (Scheme 27). 

Alkene ligand rotations will be considered first. The trigonal bipyramidal complexes [(i7 -olefin)(dad)Fe(CO)2] (dad = 1,4-diaza-l,3-diene) exhibit olefin rotation with activation energies in the range 48-75 kJ mol in most cases. The... 

Matsuo, Y Mashima, K. Tani, K. Half-metalloeene tantalum complexes bearing methyl methacrylate (MMA) and 1,4-diaza-l,3-diene ligands as MM A polymerization catalysts. Angew. Chem., Int. Ed. Engl. 2001,40, 960-962. 

Scheme 4-308. Dimerization of butadiene catalyzed by an (1,4-diaza-l,3-diene)iron complex.

An iron catalyst formed from a C2-symmetric l,4-diaza-l,3-diene-FeCl2 complex and an organomagnesium compound promotes the cyclo-codimerization of isoprene and trans-1,3-pentadiene to give 1,7-di-methyl-1,5-cyclooctadiene in a fair ee (Scheme 110) (270). 

An investigation concerning intramolecular aza Diels-Alder reactions of 3-(co-alkynyl)-l,2,4-triazines has been published by Taylor et al. [327] and trichloro-1,2,4-triazine has been introduced as novel triazine diene recently [328]. 1,2,4-Triazines are a useful alternative of 1,4-diaza-l,3-butadienes with regard to the aforementioned synthesis of pyrazines since Taylor s group has found them to undergo cycloadditions with nitriles followed by extrusion of nitrogen [329]. This reaction is noteworthy since it is a Diels-Alder reaction of both electron-deficient diene and dienophile. 

A number of pentavalent trispyrazolylborate derivatives (see Tris(pyrazolyl)borates) have been reported, especially for niobium. Most of them are monomeric Tp MCl2X (X = O, NR) derivatives, jj and jj -pyrazolato (16) or 1,2,4-triazolato derivatives have been prepared as potential sources of nitrides for CVD. The reactions between dilithium l,4-diaza-l,3-diene and pentachlorides have been investigated. ... 

Diaza-l, 3-butadiene (a-Diimine) Ligands Their Coordination Modes and the Reactivity of Their Metal Complexes, 21, 152 Diene-Iron Carbonyl Complexes, 1, 1... 

The palladacyclopropene 12 would most probably be an intermediate en route to 13, and, indeed, 1 1 complexes of palladium and DMAD have been obtained and characterized by NMR and IR spectroscopy with stabilizing ligands such as triphenylphosphine and A,A -di-tert-butyl-l,4-diaza-l,3-diene present (Scheme 4). Unfortunately, however, it was... 

Highly functionalized, biologically important 1,2,4,5-tetrazepine derivatives 256 have been prepared in the first example of a catalyst-free [4 + 3] cycloaddition reaction between in situ formed 1,2-diaza-l, 3-dienes and C,N-cyclic azomethine imine ylides 255 (13CC7905). After reaction optimization and substrate scope studies, this catalyst-free [4 + 3] cycloaddition was extended to the use of cychc hydrazones as substrates, such as 254a and 254b, which form the in situ generated azoalkenes, to yield the respective polycyclic products 256. 

To a stirred solution of 1,2-diaza-l,3-diene (1 1 mmol) in chloroform was added amine (2 1 mmol), and stirred at room temperature. On disappearance of the reagents (within 0.1-0.5 h as checked by TLC), isothiocyanate 3 was added to the reaction vessel and the reaction mixture was allowed to stand at room temperature until completion of the reaction (0.5-18 h). In some cases solid thiohydantoin derivative 4 was obtained by precipitation from the reaction medium or by crystallization from appropriate solvents, while, in other cases, it was obtained after removal of chloroform in vacuo and subsequent column chromatographic purification (cyclohexane/ethyl acetate mixtures). All the products were characterized on the basis of elemental analyses and detailed spectral studies. 

To astirred solution of 1,2-diaza-l,3-diene (1 1 mmol)indichloromethane(4 mL)takenina25 mL flask was added trimethylsUyl azide (2 1.1 mmol), followed by the addition of Cu(0Ac)2 -H20 (0.2 mmol) and the reaction mixture was stirred at room temperature until the complete formation of organic azide (TLC check). The reaction flask was then immersed in an ice bath (0 °C), and a cooled solution of triphenylphosphine (3 1.0 mmol) in CH2CI2 (1 mL) was added drop-wise the reaction mixture was then stirred at room temperature until the disappeareance of organic azide (monitored by TLC). The reaction mixmre was cooled again to 0 °C, and isocyanate or isothiocyanate derivative (4 1.1 mmol) was slowly added. Within 5 min, the reaction mixture was taken at room temperature and stirred until the complete formation of the triphenylphosphine oxide or triphenylphosphine thioxide as byproduct (TLC check). After removal of the solvent in vacuo, the... 

The cyclodimerization of butadiene forming a mixture of cycloocta-1,5-diene and vinylcyclohexene can be catalyzed by a (l,4-diaza-l,3-diene)iron complex in the presence of a Grignard reagent (Scheme 4-308). ... 

Cycloaddition reactions of l,3,4-oxadiazin-6-ones 97 (R = Ph, R = Ar), via their 2,3-diaza-l,3-diene functionality, are observed by treatment with dipolarophiles. Thus, 2,5-diaryl-l,3,4-oxadiazines 97 react with diaryl nitrilimines 115, which are liberated in situ from the corresponding hydrazonoyl chlorides 114 and triethylamine, to give 1//-1,2,4-triazole A -imines 118 and open-chain products 119 <1996JHG591>. It is reasonable to conclude that intermediates 116 are formed initially from cycloaddition across the adjacent carbonyl-carbon nitrogen double bond and that subsequent CO abstraction gives 177-1,2,4-triazole A -imine derivatives 118. The open-chain adducts 119 are formed from intermediates 117, which result from the reaction of 115 at the carbonyl double bond of the oxadiazinones 97 (Scheme 15). 

TMSK has also been employed in the synthesis of p5ra-nones via a [4 + 2] cycloaddition with an electron-rich 1,3-diene (eq 21). Alternatively, 2 equiv of TMSK can be used to react with an enamine to afford pyranones or the corresponding resorcinols. 1,3-Diaza-l,3-dienes have also been reacted with TMSK in an analogous way to furnish 4(3H)-pyrimidinones. ... 

Reaction type 3 (equation 10), where the complete hetero-l,3-diene skeleton is incorporated into the newly formed ring system, occurs with compounds having both a nucleophilic center and an electrophilic center If these two functionalities are in positions 1 and 2, various types of six-membered ring systems become accessible 4,4-Bis(trifluoromethyl)-I,3-diaza-1,3-butadienes require only room temperature to react with acetyl cyanide to yield l,4,5,6-tetrahydropynmidin-6-ones [96] Likewise, certain open-chain 1,3-diketones (acetylacetone and acetoacetates) and the heterodiene form six-membered nng systems [97] (equation 19)... 

In a series of studies of the spectroscopy and photochemistry of nickel(O) -a-diimine complexes, the structural differences among the complexes NiL2 and Ni(CO)2L (L Q-diimine) have been examined by means of molecular orbital calculations and electronic absorption Raman resonance studies.2471, 472 Summing up earlier work, the noninnocence of a-diimine ligands with a flat — N=C—C=N— skeleton in low-valent Ni chemistry and the course of substitution reactions of Ni° complexes with 1,4-diaza-1,3-dienes or a,a -bipyridine have been reviewed.2473... 

Thus, ketenes (2) can react as dienophiles with (E)-l,3-diazabuta-l,3-dienes (E)-(25) to yield either [4 + 2] cycloaducts (26) or (27) depending on the participation of the C = C or C = O moieties of the ketenes (Scheme 7). Claisen rearrangement of 3,6-dihydro-2-methylene-2//-l,3,5-oxadiazines (27) yields the p-lactams (28). Alternatively, reaction between ketenes (2) and (Z)-l,3-diaza-buta-1,3-dienes (Z)-(25) leads to the usual zwitterionic intermediates (29), whose conrotatory electrocyclation leads to p-lactams (28). No computational data including solvent effects have been reported for these reactions. 

The Rh-catalysed intermolecular [4+2] cycloaddition of a diene and a terminal alkyne affords the l,4-disubstituted-l,3-cyclohexadiene 58 via 57 [18], The 1,2,6-trisubstituted-l,4-cyclohexadiene 60 is obtained by the Fe-catalysed [4+2] cycloaddition of dienes and internal alkynes. The catalyst 59 is prepared by the reaction of a 1,4-diaza-1,3-diene complex of FeCl2 59 with EtMgBr [19]. 

Summary Copyrolytic gas-phase reactions of l,l,2,2-tetra(alkoxy)- and tetrakis-(dimethylamino)dimethyldisilanes with dienes, heterodienes, and heterotrienes in a flow-system furnish a number of unsaturated silicon heterocycles via silylene-intermediates with the exception of 1,4-diaza- and 1,4-oxazadienes, yielding 40-65 % of 1,3,2-diaza- and l,3,2-oxazasilacyclopent-4-enes, respectively, mixtures of diastereoisomeric 1-oxa- or 1-aza-2-silacyclopent-4-enes and -3-enes are formed. Conjugated oxatrienes were found to undergo additionally [6+l]-cycloadditions giving l-oxa-2-silacyclohepta-4,6-dienes. 

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