N-heterocyclics aromatization

Huvaere, K., and Skibsted, L. H. (2009) Light-Induced Oxidation of Tryptophan and Histidine. Reactivity of Aromatic N-Heterocycles toward Triplet-Excited Flavins, Journal of American and Chemical Society, Vol. 131, (May 2009) pp. 8049-8060, ISSN 0002-7863. 

Since most Ni1 species with simple N-donor ligands are prone to disproportionation into Ni° and Ni11, relatively few Ni1 complexes with nonmacrocyclic N-donor ligands have been reported. Formation of Ni1 species is in most cases proposed on the basis of electrochemical data, although ligand-centered redox processes have to be considered. The ligands usually contain imine donor atoms or aromatic N-heterocycles, which because of their 7r-acceptor ability favor stabilization of lower oxidation states. 

Relevant examples of enantioselective hydrogenation of aromatic N-heterocycles are given below. Scheme 16.21 shows the hydrogenation of a 2-ester substituted piperazine to the corresponding 2-substituted pyrazine with a catalyst... 

A. Kiener, Biosynthesis of functionalized aromatic N-heterocycles, CHEMTECH 1995, 25, 31-35. 

Some variants of our central reaction have been discovered. Consistent with the notion that NHC ligands are stable in the absence of aromatic jr-stabilization, a non-aromatic N-heterocycle, 4,4-dimethyl-2-oxazoline (3), can be added to olefins in the presence of a rhodium catalyst [10]. The optimized reaction conditions are especially mild, making this an effective method for preparation of protected carboxylic acids. 

Modelling the hydrodenitrogenation of aromatic N-heterocycles in the homogeneous phase 01EJI43. 

At elevated temperatures 2 moles of dialkyl alane react with nitriles up to the amine stage. The dialkyl-dialkylamino alanes, R NR fCHaR"), resulting from azomethines form molecular compounds with strong donors. These are colored if the donor is an azomethine or an aromatic N heterocycle and may be used for the quantitative determination of A1H groups in organic aluminum compounds 191). Complex salts such as Li[(RO)jAlH] 37, 38) or Na iC s AlIR] 287) may be used in the preparation of aldehydes instead of diisobutylalane (cf. Section V,D,3b). 

Introduction of heteroatoms, e. g. N, S, or O, into hydrocarbon molecules adds substantial value, and new routes for such reactions are of continuous interest to the chemical industry. The two main classes of aromatic N-containing hydrocarbons are the arylamines and the aromatic N-heterocyclic compounds. The aryl-amines, which are required industrially, are manufactured by nitration of aromatics to nitroaromatics, followed by hydrogenation to arylamines [1,2]. Because of the lower demand for aromatic heterocycles than for arylamines, coal tar is still an important source of pyridine and methylpyridines (picolines). Increasing demand for aromatic heterocyclic compounds has led to processes in which aldehydes and ketones are condensed with NH3 to furnish pyridine and alkylated pyridines [3,4]. 

The chemistry of edta-type complexes of Ru(III) is dominated by their lability toward the aqua-substitution reaction (Scheme 1), which affords a facile and straightforward synthesis to mixed ligand complexes. Matsubara and Creutz jilso observed the unusual lability of the [Ru(edta)(H20] (edta =ethylenedi-aminetetraacetate) complex toward substitution with various aromatic N-heterocycles (3). The reaction was characterized by the rapid formation of a 1 1 (metal to ligand) substituted product complex, [Ru(edta)L]. 

Coniugate additions to vinyl-substituted aromatic N-heterocycles 12SL1590. 

Utihzing the same catalyst complex, aromatic N-heterocycles, an alcohol, and thiols also act as nucleophiles to afford the corresponding products in moderate to good yields (34-85%) with high to excellent enantioselectivities (74-96% ee) in water. ... 

Ghosh P, Mandal A et al (2013) y-Maghemite-silica nanocomposite a green catalyst for diverse aromatic N-heterocycles. Catal Commun41 146-152... 

The decision was taken to explore and optimize this random lead by the synthesis of analogs. The only published work on similar 6-membered-aromatic-N-heterocyclic compotmds as ftmgicides was the triarimol project of Eli Lilly. But although most of the Eli Lilly patents include compounds with a two-carbon bridge between a halogen substituted phenyl ring and the N-heterocyclic system, compotmds with an one-carbon bridge seem always preferred (. ... 

Bianchini C, Meli A, Vizza F. Modelling the hydrodenitrogenation of aromatic N-heterocycles in the homogeneous phase. Eur J Inorg Chem. 2001 43—68. 

Carver CT, Diaconescu PL. Ring-opening reactions of aromatic N-heterocycles by scandium and yttrium alkyl complexes. J Am Chem Soc. 2008 130 7558-7559. 

Diaconescu PL. Reactions of aromatic N-heterocycles with d°f-metal alkyl complexes supported by chelating diamide hgands. Acc Chem Res. 2010 43 1352-1363. 

Yi W, ZhangJ, Huang S, Weng L, Zhou X. Reactivity of TpMe2-supported yttrium alkyl complexes toward aromatic N-heterocycles ring-opening or C=C bond formation directed by C-H activation. Chem Eur J. 2014 20 867-876. 

Carver CT, Williams BN, Ogilby KR, Diaconescu PL. CoupHng of aromatic N-heterocycles mediated by group 3 complexes. Organometallics. 2010 29 835-846. 

Zhang Y, Zhang J, Hong J, Zhang F, Weng L, Zhou X. Versatile reactivity of p-diketiminato-supported yttrium dialkyl complex toward aromatic N-heterocycles. Organometallics. 2014 33 7052-7058. 

To verify that this is purely based on the hydrogen-bond strength of the donors and acceptors, it is important to establish whether the balance between an aromatic N-heterocycle and an amide can be reversed by lowering sufficiently the hydrogen-bond accepting property of the aromatic nitrogen atom. With this in mind, we synthesized a set of ditopic supramolecular reagents that combined an amide moiety with a very weak base, pyrazole. The idea was that if the basicity of the... 

There are three integral components of DNA sugar, phosphate backbone, and aromatic N-heterocyclic DNA bases covalently bonded to the sugar. Two strands of the DNA... 

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