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An oxidative cyclization of electron‐rich α‐arylhydrazones promoted by phenyliodine bis(trifluoroacetate) (PIFA) has been accomplished. This metal‐free, chemoselective transformation allows to obtain synthetically and medicinally important N‐amino‐1H‐indoles, obviating the need for pre‐functionalization of substrates. [ABSTRACT FROM AUTHOR]

A novel protocol for the assembly of polysubstituted 2,3‐dioxo‐1,4,5,6‐tetrahydropyrazines and 2,3‐dioxo‐hydro‐1H‐cycloalkyl[b]pyrazines has been developed by the sequential three‐component reaction of primary aliphatic amines, 1,2‐diaza‐1,3‐dienes (DDs) and oxalyl chloride. This synthetic sequence proceeds by initial aza‐Michael addition of the amine to the azo‐ene compounds and subsequent ring closure involving the oxalyl chloride. The ready availability of the starting materials as well as the high level of practicability of the reaction and work‐up make this approach an attractive opportunity towards these uncommon systems. [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]

New and valuable indole based sulfurylated bi‐heterocyclic systems such as 4‐((1H‐indol‐2‐yl)thio)‐5‐oxo‐4,5‐dihydro‐1H‐pyrazoles and 3,3‐dimethyl‐3′H‐spiro‐indoline‐2,2′‐thiazoles are regioselectively obtained under very mild conditions employing 1,2‐diaza‐1,3‐dienes and not smelly indoline 2‐thiones as starting materials. [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]

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]

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]

A facile method for the synthesis of pyrrolino-tetrahydroberberine derivatives starting from 1,2-diaza-1,3-dienes and dihydroberberines is reported. The synthesis is a cascade reaction involving a Michael-type addition of the enamine moiety of dihydroberberine to an azo-ene system, followed by nitrogen cyclization on the resulting iminium ion. [ABSTRACT FROM AUTHOR]

The multicomponent 1,3-dipolar cycloaddition of different 1,2-diaza-1,3-dienes with in-situ-generated azomethine ylides produces 1,2,4-triazepines or pyrrolidines by [3+4] or [3+2] cycloadditions, respectively. The regioselectivity is controlled by the electron-withdrawing group bound to the azo moiety of the 1,2-diaza-1,3-diene, which promotes exclusively the [3+4] cycloaddition. When the electron-withdrawing group is replaced with a phenyl group, only a [3+2] cycloaddition occurs. [ABSTRACT FROM AUTHOR]

The rapid and expedient assembly of three new classes of biheterocycles of biological interest, viz. indole-imidazoles 4, indole-pyrroles 6 and indole-triazoles 8 was accomplished using different combinations of tryptamines, 1,2-diaza-1,3-dienes, aldehydes, and/or alkynes as readily available building blocks. Twenty-six derivatives were thus prepared in excellent yields (up to 100 %). The products were screened for in-vitro biological studies. Some of these revealed promising anticancer activity against MCF7 and Caco-2 human tumor cell lines. [ABSTRACT FROM AUTHOR]

A sulfa-Michael addition/formal [3+3] annulation cascade reaction between 1,4-dithiane-2,5-diol and 1,2-diaza-1,3-dienes by a one-pot base-catalysed strategy was developed. This metal-free and odourless method provides a practical and facile approach to 1,4-thiazines obtained in total atom economy and in quantitative yields. Furthermore, the synthesis could be scaled-up to the gram scale. [ABSTRACT FROM AUTHOR]

A mild, sequential multicomponent reaction strategy for the regioselective synthesis of functionalized pentasubstituted pyrroles from readily accessible primary amines, 1,2-diaza-1,3-dienes, and 2,3-allenoates, has been developed. The process allows a [1N+2C+2C] annulation to be achieved through two sequential hydroamination reactions followed by an enamine-carbocyclization. Moreover, allenoates, as synthetic equivalents of monoactived alkynes, permit the specific preparation of multifunctionalized pyrroles. [ABSTRACT FROM AUTHOR]

The NaH-catalyzed Michael addition of N-arylhydrazones (II) with 1,2-diaza-1,3-dienes leads to novel β-azohydrazones (III), which are converted into hydroxyl pyrazoles (IV) by a ring closure reaction in the presence of a stoichiometric amount of NaH. [ABSTRACT FROM AUTHOR]