Dipolar and V-shaped structures incorporating methylenepyran and diazine fragments

Thirteen novel dipolar and V-shaped chromophores with pyranylidene electron-donating part, diazine electron-withdrawing part and various π-linkers were synthesized. The extent of intramolecular charge transfer, structure-property relationships and optical properties were further investigated by UV/Vis absorption, electrochemistry, and DFT calculations.     

Triplet states via intermediate neglect of differential overlap: Benzene,pyridine and the diazines

The intermediate neglect of differential overlap technique is modified and applied to the calculation of excited triplet states. The resulting method generally reproduces the transition energies of the better-classified observations within a rms error of 1000 cm^–1. Trends are well reproduced, and the calculated orders ofn-* and -* triplet states are in good accord with the experimental information to date.The method is applied to benzene and the azines. The lowest four triplet states of benzene are calculated in good accord with experiment. Pyridine is calculated to have an-* triplet nearly degenerate with the lowest lying -* triplet, corroborating suggestions of Japar and Ramsay based on experimental information. A detailed analysis is made of the diazines, and assignments are suggested for the higher lying triplet states not yet classified or not yet observed.     

The Behavior of Phosphorus Reagents Towards Substituted Diazine and Hydrazine Derivatives

Summary. The reaction of dibenzoyldiazine with phosphorus ylides afforded the new 2-[(benzoylhydrazono)phenylalkyl]but-2-enedioic acid dialkylesters. Moreover, ethyl-2(triphenylphosphoranylidene)propionate reacts with dibenzoyldiazine to give the olefinic compound and triphenylphosphine oxide. On the other hand, oxovinylidene-triphenylphosphorane reacts with dibenzoyldiazine to give a new phosphorane adduct. Trialkyl phosphites react with dibenzoyldiazine to yield the dialkyl phosphonate products. The reaction of dibenzoylhydrazide with Wittig reagents gave rise to the new 3,7-diphenylpyrazolo[1,2-α]pyrazole-1,5-diones. Possible reaction mechanisms are considered, and the structural assignments are based on analytical and spectroscopic results.     

Synthesis of new polyaza heterocycles. Part 42: Diazines

Using Pd-catalyzed Stille cross-coupling reactions, we report here the synthesis of various mono- or bis(tri-n-butylstannyl)diazines which were reacted with various halogenated diazines to access to various polyaza heterocyclic derivatives.     

Reactivity of asymmetric benzo-condensed diazines with nitrilimine dipoles in the 1,3-dipolar cycloaddition reactions

The reactivity of asymmetric benzo-condensed diazines in the 1,3-dipolar cycloaddition reactions with nitrilimines was investigated. The results demonstrated that, at variance with the symmetric quinoxaline, a certain grade of diastereoselectivity emerged. Moreover in the case of the 5-methylquinoxaline and quinazoline a mono-cycloadduct was obtained.     

α-(3,7-Dioxa-r-1-azabicyclo[3.3.0]oct-c-5-ylmethoxy)-diazines. Part 2: Functionalisation via directed ortho-metallation and cross-coupling reactions

The functionalisation of the title compounds via regioselective Directed ortho-Metallation (DoM) and cross-coupling reactions is studied. The compatibility of the 3,7-DiOxa-r-1-AzaBicyclo[3.3.0]Oct-c-5-ylmethoxy system (DOABO-CH₂O) to typical reaction conditions is established. Its role as Directed ortho-Metallation Group (DoMG) is examined, including competition with classical DoMGs, chlorine and methoxy. The chelating ability of some functionalised terms such as DOABO-CH₂O substituting chiral diarylmethanols and polyaza analogues of 2,6-terpyridine is discussed as intramolecular steric relationships determining configuration and aptitude to bind selectively transition metals, respectively.     

α-(3,7-Dioxa-r-1-azabicyclo[3.3.0]oct-c-5-ylmethoxy)-diazines. Part 1: Synthesis and stereochemistry. Extension to s-triazine series

The general and efficient synthesis of the title compounds, consisting of the (selective) replacement of chlorine in commercial α-chlorodiazines and cyanuryl chloride by the 3,7-dioxa-r-1-azabicyclo[3.3.0]oct-c-5-ylmethoxy group (Williamson method) is described. The stereochemistry of this new series of derivatives is analysed in terms of different conformational chirality exhibited in solution (¹H NMR) versus solid state (X-ray diffractometry), meso against chiral forms, respectively. In solid state, the inclusion capacity of some chiral networks as well as their supramolecular aggregation is pointed out. A good correlation between rotameric behaviour of the c-5-di(s-tri)diazinyloxymethyl group in the two states is found.     

From Luminescent Complexes to Framework Formation from Ln‐trichlorides and Pyrazine

The three‐dimensional framework ³_∞[LaCl₃(pyz)] and the dimeric complexes [Ln₂Cl₆(pyz)(py)₆] · 2pyz (Ln = Sm, Er) were obtained from solvothermal reaction of the respective chlorides LnCl₃ with pyrazine (pyz) in pyridine (py) at 200 °C. In the compounds, pyrazine ligands interlink Ln‐cations: in the complexes to a dimer, in the framework structure to 2D sheets, which are further connected via chloride bridges. This results in an uninodal 6‐c net with the point symbol (4⁸.6⁷) and a variant of the sxa topology. The dimeric complexes exhibit 4f‐based emission in the visible for samarium and in the NIR for erbium, both sensitized by the pyrazine ligands, as mechanistic insights show.     

Comprehensive experimental investigation of mechanically induced 1,4-diazines synthesis in solid state

Compared mechanosynthesis of two condensed 1,4-diazines were investigated in ball milling conditions from o-phenylenediamine. ¹³C CP-MAS NMR revealed a hemiaminal intermediate for dibenzo[a,c]phenazine synthesis accumulated under mechanical action, as confirmed by calorimetry. Such intermediate, which is not detected in the case of 2,3-diphenylquinoxaline synthesis, provides experimental evidence of a concerted reaction between highly reactive mechanically-excited diamine and 9,10-phenanthrenequinone.     

Selective formation of heteroaryl thioethers via a phosphonium ion coupling reaction

Heteroaryl thioethers, comprised of pyridines and diazines, are an important class of compounds with relevance to medicinal chemistry. Metal-catalyzed cross-couplings and S_NAr reactions are traditionally used to form C–S bonds in these systems but are limited by available halogenated precursors. An alternative approach is presented where pyridines and diazines are transformed into heterocyclic phosphonium salts and then C–S bonds are formed by adding thiolate nucleophiles. The process is 4-selective for pyridines, simple to execute and can be used to make derivatives of complex pharmaceuticals.