Site-selective C–H functionalization in chemical feedstocks is a challenging and useful reaction in the broad field of chemical research. Here, we report a modular photochemical platform for the ...site-selective C–H pyridylation of unactivated hydrocarbons via the unique synergistic effects of triplet excited anthraquinone and an amidyl radical-based reverse hydrogen atom transfer (RHAT) agent. The selective pyridylation of tertiary and secondary C(sp3)–H bonds in abundant chemical feedstocks was achieved by employing various N-aminopyridinium salts in a highly selective fashion, thus providing a new catalytic system for the direct construction of high-value-added compounds under ambient reaction conditions. Moreover, this operationally simple protocol is applicable to a variety of linear-, branched-, and cyclo-alkanes and more complex molecules with high degrees of site selectivity under visible-light conditions, which provides rapid and straightforward access to versatile synthons for upgrading feedstocks under mild, metal-free reaction conditions.
Reported herein is a modular, NiH-catalyzed system capable of proximal-selective hydroamination of unactivated alkenes with diverse amine sources. The key to the successful implementation of this ...approach is the promotion of NiH insertion into even highly substituted olefins via coordination of the bidentate directing group to the nickel complex. A wide range of primary and secondary amines can be installed in both internal and terminal unactivated alkenes with excellent regiocontrol under the optimized reaction conditions. This protocol is flexible and general for the preparation of a variety of valuable β- and γ-amino acid building blocks that would otherwise be difficult to synthesize. The utility of this transformation was further demonstrated by the site-selective late-stage modification of complex and medicinally relevant molecules. Combined experimental and computational studies illuminate the detailed reaction mechanism.
C2- and C5-alkynylated quinolone scaffolds are core structures of numerous biologically active molecules. Utilizing TIPS-EBX as an alkynylating agent, we have developed an efficient and ...site-selective C5 alkynylation of 4-quinolones that is directed by the weakly coordinating carbonyl group. In addition, Ru(II) catalyzed C2-selective alkynylation was successfully realized via N-pyrimidyl group-directed cross-couplings to access valuable C2-alkynylated 4-quinolones. This strategy provides direct access to the C2 or C5 alkynylated 4-quinolones. Furthermore, the reaction was applied to isoquinolones for C3-selective alkynylation.
A
bstract
The standard paradigm of collisionless cold dark matter is in tension with measurements on large scales. In particular, the best fit values of the Hubble rate
H
0
and the matter density ...perturbation
σ
8
inferred from the cosmic microwave background seem inconsistent with the results from direct measurements. We show that both problems can be solved in a framework in which dark matter consists of two distinct components, a dominant component and a subdominant component. The primary component is cold and collisionless. The secondary component is also cold, but interacts strongly with dark radiation, which itself forms a tightly coupled fluid. The growth of density perturbations in the subdominant component is inhibited by dark acoustic oscillations due to its coupling to the dark radiation, solving the
σ
8
problem, while the presence of tightly coupled dark radiation ameliorates the
H
0
problem. The subdominant component of dark matter and dark radiation continue to remain in thermal equilibrium until late times, inhibiting the formation of a dark disk. We present an example of a simple model that naturally realizes this scenario in which both constituents of dark matter are thermal WIMPs. Our scenario can be tested by future stage-IV experiments designed to probe the CMB and large scale structure.
A straightforward synthetic strategy to construct biologically relevant phenanthridinones and quinolinones was developed via visible-light-promoted direct oxidative C–H amidation. In this ...photocatalytic system, amidyl radicals can be generated by homolysis of the N–H bond of simple amide precursors via single-electron transfer under blue LED illumination, which leads to oxidative intramolecular C–H amidation. Moreover, an efficient synthetic strategy using a photocascade enabled facile assembly of quinolinone structures through a catalytic sequence involving triplet energy (E T) transfer-based E/Z olefin isomerization and subsequent photocatalytic generation of amidyl radical intermediates.
Remote functionalization of alkenes via chain walking has generally been limited to C(sp
)-H bonds α and β to polar-functional units, while γ-C(sp
)-H functionalization through controlled alkene ...transposition is a longstanding challenge. Herein, we describe NiH-catalyzed migratory formal hydroamination of alkenyl amides achieved via chelation-assisted control, whereby various amino groups are installed at the γ-position of aliphatic chains. By tuning olefin isomerization and migratory hydroamination through ligand and directing group optimization, γ-selective amination can be achieved via stabilization of a 6-membered nickellacycle by an 8-aminoquinoline directing group and subsequent interception by an aminating reagent. A range of amines can be installed at the γ-C(sp
)-H bond of unactivated alkenes with varying alkyl chain lengths, enabling late-stage access to value-added γ-aminated products. Moreover, by employing picolinamide-coupled alkene substrates, this approach is further extended to δ-selective amination. The chain-walking mechanism and pathway selectivity are investigated by experimental and computational methods.
Anomaly inflow and holography Hong, Sungwoo; Rigo, Gabriele
The journal of high energy physics,
05/2021, Volume:
2021, Issue:
5
Journal Article
Peer reviewed
Open access
A
bstract
We systematically study the perturbative anomaly inflow by the bulk Chern-Simons (CS) theory in a slice of five-dimensional anti-de Sitter spacetime (AdS
5
). The introduction of UV and IR ...3-branes makes the anomaly story remarkably rich and many interesting aspects can be obtained, including weakly gauging and spontaneous symmetry breaking of the global symmetries of the dual 4D CFT. Our main contribution is to provide a unified and comprehensive discussion of the subject, together with a detailed description of the dual CFT picture for each case. To this end, we employ a gauge-fixed effective action suitable for a holographic study, which allows us to incorporate general UV and IR boundary conditions (BCs). As part of the process, we reproduce many known results in the literature, such as ’t Hooft anomaly matching for unbroken symmetry (Neumann IR-BC) and (gauged) Wess-Zumino-Witten (WZW) action for broken symmetry (IR-BC breaks the bulk group
G → H
). In addition, we show that anomaly matching occurs for ABJ anomalies as well as ’t Hooft anomalies, which suggests anomalies inflowed from the bulk CS theory are necessarily free of mixed anomalies with the confining gauge force of the 4D dual CFT. In the case of broken symmetry, we prove that the “would-be” Goldstone bosons associated with the weakly gauged symmetry are completely removed by a proper field redefinition, provided the anomaly from the bulk is exactly cancelled by the boundary contribution, hence confirming the standard expectation. Moreover, we present a holographic formulation of Witten’s argument for the quantization condition for the WZW action, and argue in favor of an alternative way to obtain the same condition using a “deformed” theory (different BCs). We work out several examples, including a product group with mixed anomaly, and identify the corresponding dual CFT picture. We consider a fully general case typically arising in the context of dynamical electroweak symmetry breaking.
A general strategy for visible‐light‐enabled site‐selective trifluoromethylative pyridylation of unactivated alkenes has been developed using pyridines and triflic anhydride (Tf2O). Intriguingly, the ...N‐triflylpyridinium salts, generated in situ from pyridines and Tf2O, serve as effective modular bifunctional reagents to install both CF3 and pyridyl groups to various olefins while controlling C4‐selectivity in radical addition to the pyridine core. This synthetic route exhibited broad substrate scope under metal‐free and mild photocatalytic conditions, granting efficient access to valuable C4‐alkylated pyridines and quinolines without requiring prefunctionalization of the reaction site.
Visible‐light‐induced site‐selective trifluoromethylative pyridylation of unactivated alkenes has been achieved using pyridines and Tf2O. Intriguingly, the generated N‐triflylpyridinium salts serve as effective modular bifunctional reagents to install CF3 and pyridyl groups to olefins while controlling C4‐selectivity in radical addition to the pyridine core to provide C4‐alkylated pyridines and quinolines.
Efficient rhodium‐catalyzed direct C–H phosphorylation of (hetero)arenes was developed. Various directing groups and a wide range of substrates, including heterocycles, can be utilized in this C–H ...phosphorylation process, allowing for the rapid installation of the phosphonate group into medicinally and biologically important privileged scaffolds. The efficient and straightforward method could serve as a new tool to streamline late‐stage C–H functionalization for preparing aryl phosphonates, which are important structural motif in synthetic and medicinal chemistry.
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