One-Pot Cross-Coupling/C-H Functionalization Reactions: Quinoline as a Substrate and Ligand through N-Pd Interaction

Regioselective Partial Hydrogenation and Deuteration of Tetracyclic (Hetero)aromatic Systems Using a Simple Heterogeneous Catalyst

The introduction of added '3-dimensionality' through late-stage functionalisation of extended (hetero)aromatic systems is a powerful synthetic approach. The abundance of starting materials and cross-coupling methodologies to access the precursors allows for highly diverse products. Subsequent selective partial reduction can alter the core structure in a manner of interest to medicinal chemists. Herein, we describe the precise, partial reduction of multicyclic heteroaromatic systems using a simple heterogeneous catalyst. The approach can be extended to introduce deuterium (again at late-stage). Excellent yields can be obtained using simple reaction conditions.

MnO2-Mediated Oxidative Cyclization of "Formal" Schiff's Bases: Easy Access to Diverse Naphthofuro-Annulated Triazines

A different type of MnO₂-induced oxidative cyclization of dihydrotriazines has been developed. These dihydrotriazines are considered as a "formal" Schiff's base. This method provided easy access to naphthofuro-fused triazine via the C-C/C-O oxidative coupling reaction. The reaction sequence comprised the nucleophilic addition of 2-naphthol or phenol to 1,2,4-triazine, followed by oxidative cyclization. The scope and limitations of this novel coupling reaction have been investigated. Further application of the synthesized compound has been demonstrated by synthesizing carbazole-substituted benzofuro-fused triazines. The scalability of the reaction was demonstrated at a 40 mmol load. The mechanistic study strongly suggests that this reaction proceeds through the formation of an O-coordinated manganese complex.

Switchable, Reagent-Controlled C(sp3)-H Selective Iodination and Acetoxylation of 8-Methylquinolines

An efficient Pd-catalyzed C(sp³)-H selective iodination of 8-methylquinolines is reported herein for the first time. Because of the versatility of organic iodides, the method offers a facile access to various C8-substituted quinolines. By slightly switching the reaction conditions, an efficient C(sp³)-H acetoxylation of 8-methylquinolines has also been enabled. Both approaches feature mild reaction conditions, good tolerance of functional groups, and a broad substrate scope.

Insights into the κ-P,N Coordination of 1,3,5-Triaza-7-phosphaadamantane and Derivatives: κ-P,N-Heterometallic Complexes and a 15N Nuclear Magnetic Resonance Survey

Complexes {[(PTA)₂CpRu-μ-CN-1κC:2κ²N-RuCp(PTA)₂-ZnCl₃]}·2DMSO (13) {[ZnCl₂(H₂O)]-(PTA-1κP:2κ²N)(PTA)CpRu-μ-CN-1κC:2κ²N-RuCp(PTA)(PTA-1κP:2κ²N)-[ZnCl₂(H₂O)]}Cl (14), [RuCp(HdmoPTA)(PPh₃)(PTA)](CF₃SO₃)₂ (20), [RuCp(HdmoPTA)(HPTA)(PPh₃)](CF₃SO₃)₃ (21), and [RuCp(dmoPTA)(PPh₃)(PTA)](CF₃SO₃) (22) were obtained and characterized, and their crystal structure together with that of the previously published complex 18 is reported. The behavior of the 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane (PTA) and 3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (dmoPTA) ligands against protonation and κN-coordination is discussed, on the basis of ¹⁵N nuclear magnetic resonance data collected on 22 different compounds, including PTA (1), HdmoPTA (7H), and some common derivatives as free ligands (2–6 and 8), along with mono- and polymetallic complexes containing PTA and/or HdmoPTA (9–22). ¹⁵N detection via ¹H–¹⁵N heteronuclear multiple bond correlation allowed the construction of a small library of ¹⁵N chemical shifts that shed light on important features regarding κN-coordination in PTA and its derivatives.

To shed light on the behavior of the triazaphosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane (PTA) and 3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (dmoPTA) upon κN coordination and N protonation, the ¹⁵N chemical shifts of 22 compounds, including PTA and a representative variety of its derivatives, piano-stool complexes, were collected by ¹H−¹⁵N heteronuclear multiple bond correlation nuclear magnetic resonance. New heterometallic complexes containing PTA were also synthesized and fully characterized.

Homologation of the Fischer Indolization: A Quinoline Synthesis via Homo-Diaza-Cope Rearrangement

We disclose a new Brønsted acid promoted quinoline synthesis, proceeding via homo-diaza-Cope rearrangement of N-aryl-N'-cyclopropyl hydrazines. Our strategy can be considered a homologation of Fischer's classical indole synthesis and delivers 6-membered N-heterocycles, including previously inaccessible pyridine derivatives. This approach can also be used as a pyridannulation methodology toward constructing polycyclic polyheteroaromatics. A computational analysis has been employed to probe plausible activation modes and to interrogate the role of the catalyst.

Competition between N and O: use of diazine N-oxides as a test case for the Marcus theory rationale for ambident reactivity

The preferred site of alkylation of diazine N-oxides by representative hard and soft alkylating agents was established conclusively using the 1H-15N HMBC NMR technique in combination with other NMR spectroscopic methods. Alkylation of pyrazine N-oxides (1 and 2) occurs preferentially on nitrogen regardless of the alkylating agent employed, while O-methylation of pyrimidine N-oxide (3) is favoured in its reaction with MeOTf. As these outcomes cannot be explained in the context of the hard/soft acid/base (HSAB) principle, we have instead turned to Marcus theory to rationalise these results. Marcus intrinsic barriers (ΔG ‡ 0) and Δr G° values were calculated at the DLPNO-CCSD(T)/def2-TZVPPD/SMD//M06-2X-D3/6-311+G(d,p)/SMD level of theory for methylation reactions of 1 and 3 by MeI and MeOTf, and used to derive Gibbs energies of activation (ΔG ‡) for the processes of N- and O-methylation, respectively. These values, as well as those derived directly from the DFT calculations, closely reproduce the observed experimental N- vs. O-alkylation selectivities for methylation reactions of 1 and 3, indicating that Marcus theory can be used in a semi-quantitative manner to understand how the activation barriers for these reactions are constructed. It was found that N-alkylation of 1 is favoured due to the dominant contribution of Δr G° to the activation barrier in this case, while O-alkylation of 3 is favoured due to the dominant contribution of the intrinsic barrier (ΔG ‡ 0) for this process. These results are of profound significance in understanding the outcomes of reactions of ambident reactants in general.