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The present method provides highly functionalized 1,3- oxathioles through an unusual base-promoted [4+1] annulation between α,α'-dioxothione, generated in situ from a phthalimide precursor, and 1,2-diaza-1,3-dienes. An intriguing scaffold comprised of spiro-fused oxathiole and pyrazolone components was also obtained in moderate yield. [ABSTRACT FROM AUTHOR]

1,2-Diaza-1,3-dienes react with electron-poor alkenes to give the corresponding tetrahydropyridazines with high regio- and stereoselectivity. Both regio- and stereoselectivity can be explained considering the interaction between the LUMO of the 1,2-diaza- 1,3-diene and HOMO-1 of the alkene. [ABSTRACT FROM AUTHOR]

The synthesis of highly functionalized α-thiohydrazones by Michael addition of 3-mercapto-2-ketones to 1,2-diazabuta-1,3-dienes is described. The phosphorylated α-thiohydrazones were hydrolyzed into β-ketophosphine oxides or phosphonates containing a mercapto ketone in the α position, while the α-thiohydrazones with a carboxylate group were subsequently transformed into 2-oxo-2,3,8,8a-tetrahydro-1H-[1,2,4]triazolo[5,1-c][1,4]thiazines by means of a domino reaction. [ABSTRACT FROM AUTHOR]

Unknown functionalized 1-aminopyrroles and 1-amino-4,5,6,7-tetrahydroindoles were prepared under mild conditions and with excellent yields by one-pot ‘conjugate addition/cyclization’ reactions of 1,3-bis(silyl enol ethers) with 1,2-diaza-1,3-butadienes. [ABSTRACT FROM AUTHOR]

A novel protocol for the efficient synthesis of 1H‐imidazo[5,1‐c][1,4]oxazines has been developed. Aza‐Michael addition of selected primary amines to 1,2‐diaza‐1,3‐dienes (DDs) combined with isothiocyanates or isocyanates in sequential 3‐CR process, affords 2‐thiohydantoins and hydantoins with suitably positioned functional groups to be used for chemoselective acid‐promoted ring‐fused formation. [ABSTRACT FROM AUTHOR]

A new and efficient synthesis of polysubstituted pyrroles by a sequential one-pot three-component reaction between primary aliphatic amines, active methylene compounds, and 1,2-diaza-1,3-dienes (DDs) is reported. The reactions were performed without catalyst and under solvent-free conditions with complete control of pathway selectivity. Notably, the ready availability of the starting materials and the high level of practicability of the reaction and work up make this approach an attractive complementary method for access to unknown poly-substituted pyrroles. [ABSTRACT FROM AUTHOR]

Substituted 1‐aminopyrroles are easily accessible by iron‐catalyzed cascade reaction of 1,2‐diaza‐1,3‐dienes. Mechanistically, a formal [3+2] cyclodimerization is hypothesized to proceed through a [4+2] cyclodimerization of 4‐substitued 1,2‐diaza‐1,3‐dienes followed by intramolecular ring closure to fused diaziridin‐pyrrolines which is successively opened to undergo a ring contraction process and consequently generate the desired pyrrole moiety. The presence of activated hydrogen in the terminal position of the azo‐enic moiety is crucial for the synthesis of pyrroles. [ABSTRACT FROM AUTHOR]

Herein, we report the successful syntheses of scarcely represented indole-based heterocycles which have a structural connection with biologically active natural-like molecules. The selective oxidation of indoline nucleus to indole, hydrolysis of ester and carbamoyl residues followed by decarboxylation with concomitant aromatization of the pyridazine ring starting from tetrahydro-1H-pyridazino[3,4-b]indole derivatives lead to fused indole-pyridazine compounds. On the other hand, non-fused indole-pyrazol-5-one scaffolds are easily prepared by subjecting the same C2,C3-fused indoline tetrahydropyridazines to treatment with trifluoroacetic acid (TFA). These methods feature mild conditions, easy operation, high yields in most cases avoiding the chromatographic purification, and broad substrate scope. Interestingly, the formation of indole linked pyrazol-5-one system serves as a good example of the application of the umpolung strategy in the synthesis of C3-alkylated indoles. [ABSTRACT FROM AUTHOR]

A wide range of substituted indoles or polycyclic derivatives containing the indole core are easily accessible by acidic treatment of aromatic amines and 1,2‐diaza‐1,3‐dienes. Unlike the related indole‐Bischler synthesis, the regioselectivity of the method here reported is unique and predictable, the yields are generally good and also electron withdrawing substituted indoles are smoothly recovered. [ABSTRACT FROM AUTHOR]

Two unprecedented approaches to amply functionalized 2‐arylamino‐5‐hydrazonothiophene‐3‐carboxylates were reported. The first one is a useful metal‐free sequential multicomponent synthesis of readily available β‐keto esters, isothiocyanates and in situ generated 4‐unsubstituted diazadienes. The second one is the basic treatment of 2,5‐dihydrothiophenes previously prepared by means of an analogous sequential multicomponent synthesis where 4‐substituted diazadienes were employed. 2‐Arylamino‐5‐hydrazonothiophene‐3‐carboxylates were assembled by a metal‐free, sequential multicomponent reaction between keto esters, isothiocyanates, and 4‐unsubstituted 1,2‐diaza‐1,3‐dienes. Alternatively, the basic treatment of dihydrothiophenes, synthesized by a similar reaction in which 4‐substituted 1,2‐diaza‐1,3‐dienes were used, regioselectively furnishes the same thiophene derivatives. [ABSTRACT FROM AUTHOR]

Indoline‐fused polycycles were synthesized through a TFA‐promoted intramolecular dearomative cyclization of indole‐tethered pyrroles. Mechanistically, the strategic carbon‐carbon bond formation is hypothesized to proceed via a Pictet‐Spengler‐type reaction wherein a reversal of conventional indole reactivity of tryptamine derivatives occurs. The synthetic versatility of this operationally simple, atom‐economic approach is demonstrated in the preparation of the pyrido[1,2‐a:3,4‐b′]diindole core of natural product homofascaplysin C. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Tetrahydroberberine (THB), otherwise known as canadine, is a natural alkaloid showing significant pharmacological properties and antioxidant protection against oxidative damage. Herein, we synthetized structurally complex THB analogues, namely pyrrolino-tetrahydroberberines (PTHBs) 4a–g , containing the pyrrolino[2,3 -b ]pyridine system, by means of the reactions of 1,2-diaza-1,3-dienes and 7,8-dihydroberberine. Aim of the study was to explore the in vitro antioxidant properties of PTHBs in comparison to THB thus to identify the most effective against free radical-induced oxidative injury, by using three different antioxidant tests: the ORAC method, the DNA nicking assay, and the DCFH-DA cellular assay. As a result, PTHB 4d emerged among the other THB analogues by exhibiting the best antioxidant properties. First, it was the only compound having an ORAC value completely comparable to that of THB, indicating the same ability to neutralize peroxyl radicals. Secondly, 4d showed an even better antioxidant capacity than THB in protecting DNA against ferrous ion-induced strand breaks. These observations were also confirmed in NCTC-2544 human keratinocytes exposed to hydrogen peroxide. Indeed, 4d protected cells against oxidation more efficiently than THB both in the short (1 and 3 h) and long (24 h) period of incubation, possibly suggesting increased cell membrane permeability and/or intracellular stability of 4d as compared to THB. [ABSTRACT FROM AUTHOR]

The coordination and photochemical properties of three hydroxypyrazole-based ligands - tert -butyl 2-[1-[3-(4-cianophenyl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate ( L1 ), tert -butyl 2-[1-[3-(3,5-bis(trifluoromethyl)phenyl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate ( L2 ), and tert -Butyl 2-[1-[3-(phenantrene-9-yl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate ( L3 ) - are reported. The ligands are fluorescent and able to coordinate a Zn(II) ion in a water/acetonitrile solvent with concomitant keto-enol tautomerism, giving rise to large Stokes shifts in the emission spectra. Ligand L1 has a peculiar double emission and can be exploited as a ratiometric fluorescent sensor. [ABSTRACT FROM AUTHOR]

Bis adducts derived from a double Michael addition of rhodanine to an azo-ene system of two molecules of 1,2-diaza-1,3-dienes (DDs) have furnished the corresponding 2,3,5,6-tetrahydro-1 H-pyrrolo[3,4- c]pyridine-1,3,6-triones by means of a CS2 extrusion/double cyclization sequence. The incorporation of two units (4 and 2 atoms) of DDs into the fused bicyclic heterocycles represents a new application of this versatile class of molecules in heterocyclic synthesis. [ABSTRACT FROM AUTHOR]

Organic dyes for dye-sensitized solar cells (DSSC) are generally constituted by chemical groups that act differently as electron donor (D) and acceptor (A) bridged by a linker. Three new push-pull D–π–A structured dyes ( SIP1 , SIP3 , SIP4 ) having imidazo[1,2- a ]pyridine heterocycles as additional π-conjugated linker were designed and synthesized. Triphenylamine (TPA) was introduced as electron-donor unit and cyanoacetic acid or double rhodanine acetic acid were employed as anchoring groups in different positions of the heterocyclic core. DSSC devices with these dyes were assembled and tested using different electrolytes and dye baths. Finally, the related photovoltaic performance was measured. The V oc values were found to influence the overall behaviour of the cells related to the electrolyte composition. DFT calculations showed a theoretical trend for the electron transfer ability of the different dyes, and correlation with the real photovoltaic performance was discussed. [ABSTRACT FROM AUTHOR]

Herein we report a domino protocol able to reach regioselectively thiazolylidene systems by combining the reactive peculiarities of both β-amidothioamides (ATAs) and 1,2-diaza-1,3-dienes (DDs). Depending on the reaction conditions and/or the nature of the residue at C4 of the heterodiene system, ATAs can act as hetero-mononucleophiles or hetero-dinucleophiles in the diversified thiazolylidene ring assembly. [ABSTRACT FROM AUTHOR]

A Pd(II)-catalyzed intramolecular oxidative C-H/C-H cross-coupling has been developed for the direct construction of valuable polycyclic heteroarene scaffolds. From a retrosynthetic point of view, the strategic formation of a C-C bond via C(sp2)-H/C(sp2)-H dehydrogenative coupling across C3,N-linked biheterocyclic precursors may be useful in de novo syntheses of indole-derived natural products and pharmaceuticals. The reaction exhibited good functional group/heterocycle tolerance, and a proposed mechanism involving an azoylpalladium complex is also supported. [ABSTRACT FROM AUTHOR]