Trapping reactions with highly unstable hydrides of antimony and bismuth

(Dipp2NacNac)Ga (Dipp2NacNac = HC{C(Me)N(Dipp)}2; Dipp = 2,6-iPr2C6H3) was used as a trapping reagent for the unstable compounds tBuSbH2 and MeBiH2 to yield (Dipp2NacNac)GaH(SbHtBu) (1) and {(Dipp2NacNac)GaH(BiMe)}2 (2). Moreover, its reactions...

Selective Functionalization of the 1H-Imidazo[1,2-b]pyrazole Scaffold. A new Potential Non-classical Isostere of Indole and a Precursor of Push-Pull Dyes

We report the full selective functionalization of the 1H-imidazo[1,2-b]pyrazole scaffold using a Br/Mg-exchange, as well as regioselective magnesiations and zincations with TMP-bases (TMP = 2,2,6,6-tetramethylpiperidyl), followed by trapping reactions with...

Catch It If You Can: Copper-Catalyzed (Transfer) Hydrogenation Reactions and Coupling Reactions by Intercepting Reactive Intermediates Thereof

The key reactive intermediate of copper(I)-catalyzed alkyne semihydrogenations is a vinylcopper(I) complex. This intermediate can be exploited as a starting point for a variety of trapping reactions. In this manner, an alkyne semihydrogenation can be turned into a dihydrogen­-mediated coupling reaction. Therefore, the development of copper-catalyzed (transfer) hydrogenation reactions is closely intertwined with the corresponding reductive trapping reactions. This short review highlights and conceptualizes the results in this area so far, with H2-mediated carbon–carbon and carbon–heteroatom bond-forming reactions emerging under both a transfer hydrogenation setting as well as with the direct use of H2. In all cases, highly selective catalysts are required that give rise to atom-economic multicomponent coupling reactions with rapidly rising molecular complexity. The coupling reactions are put into perspective by presenting the corresponding (transfer) hydrogenation processes first.1 Introduction: H2-Mediated C–C Bond-Forming Reactions2 Accessing Copper(I) Hydride Complexes as Key Reagents for Coupling Reactions; Requirements for Successful Trapping Reactions 3 Homogeneous Copper-Catalyzed Transfer Hydrogenations4 Trapping of Reactive Intermediates of Alkyne Transfer Semi­hydrogenation Reactions: First Steps Towards Hydrogenative Alkyne Functionalizations 5 Copper(I)-Catalyzed Alkyne Semihydrogenations6 Copper(I)-Catalyzed H2-Mediated Alkyne Functionalizations; Trapping of Reactive Intermediates from Catalytic Hydrogenations6.1 A Detour: Copper(I)-Catalyzed Allylic Reductions, Catalytic Generation of Hydride Nucleophiles from H2 6.2 Trapping with Allylic Electrophiles: A Copper(I)-Catalyzed Hydro­allylation Reaction of Alkynes 6.3 Trapping with Aryl Iodides7 Conclusion

Functionalized Allenes: Generation by Sigmatropic Rearrangement and Application in Heterocyclic Chemistry

The present review article summarizes the synthesis of allenes, which bear an adjacent functional group, by [3,3]- or [2,3]-sigmatropic rearrangement of appropriate propargyl substrates. Functionalized allenes, such as allenyl isothiocyanates, isoelenocyanates, isocyanates, thiocyanates, azides, azo compounds and others, are easily available by these methods. In several cases, however, the title compounds show high reactivity, which leads to rapid intermolecular or intramolecular successive reactions. Consequently, synthesis of the allenes by sigmatropic rearrangement has to be combined with special techniques, for example, flash vacuum pyrolysis or in situ generation and trapping reactions. The high tendency of the presented functionalized allenes to undergo cyclization reactions can be utilized to prepare heterocyclic products, for instance, thiazoles, selenazoles, 1,2,3-triazoles and pyrazoles. The synthesis of functionalized 1,3-butadienes by a second sigmatropic rearrangement of the title compounds is also successful.

Diverse One-Pot Electrophilic Trapping Reactions of 2-Quinolyl­zincates with Acyl Chlorides and Allyl Iodide

The tandem acylation reactions of 2-quinolylzincates under one-pot reaction conditions facilitated the formation of biologically active (Z)-3-alkylidenephthalides and multifunctionalized quinoline derivatives at specific positions. The reactions of these zincates with allyl iodide produced three different types of temperature- and alkyl-ligand-dependent C-2 homologated quinolines. The reaction mechanisms for the formation of the presented products from 2-quinolylzincates are also proposed in detail.

From Quinoxaline, Pyrido[2,3-b]pyrazine and Pyrido[3,4-b]pyrazine to Pyrazino-Fused Carbazoles and Carbolines

2,3-Diphenylated quinoxaline, pyrido[2,3-b]pyrazine and 8-bromopyrido[3,4-b]pyrazine were halogenated in deprotometalation-trapping reactions using mixed 2,2,6,6-tetramethyl piperidino-based lithium-zinc combinations in tetrahydrofuran. The 2,3-diphenylated 5-iodo- quinoxaline, 8-iodopyrido[2,3-b]pyrazine and 8-bromo-7-iodopyrido[3,4-b]pyrazine thus obtained were subjected to palladium-catalyzed couplings with arylboronic acids or anilines, and possible subsequent cyclizations to afford the corresponding pyrazino[2,3-a]carbazole, pyrazino[2′,3′:5,6] pyrido[4,3-b]indole and pyrazino[2′,3′:4,5]pyrido[2,3-d]indole, respectively. 8-Iodopyrido[2,3-b] pyrazine was subjected either to a copper-catalyzed C-N bond formation with azoles, or to direct substitution to introduce alkylamino, benzylamino, hydrazine and aryloxy groups at the 8 position. The 8-hydrazino product was converted into aryl hydrazones. Most of the compounds were evaluated for their biological properties (antiproliferative activity in A2058 melanoma cells and disease-relevant kinase inhibition).