An official website of the United States government
Abstract The regioselective conversion of C−H bonds into C−Si bonds is extremely important owing to the natural abundance and non‐toxicity of silicon. Classical silylation reactions often suffer from poor functional group compatibility, low atom economy, and insufficient regioselectivity. Herein, we disclose a template‐assisted method for the regioselectivepara silylation of toluene derivatives. A new template was designed, and the origin of selectivity was analyzed experimentally and computationally. An interesting substrate–solvent hydrogen‐bonding interaction was observed. Kinetic, spectroscopic, and computational studies shed light on the reaction mechanism. The synthetic significance of this strategy was highlighted by the generation of a precursor of a potential lipophilic bioisostere of γ‐aminobutyric acid (GABA), various late‐stage diversifications, and by mimicking enzymatic transformations.
more »
« less
Ligand control of regioselectivity in palladium-catalyzed heteroannulation reactions of 1,3-Dienes
Abstract Olefin carbofunctionalization reactions are indispensable tools for constructing diverse, functionalized scaffolds from simple starting materials. However, achieving precise control over regioselectivity in intermolecular reactions remains a formidable challenge. Here, we demonstrate that using PAd2nBu as a ligand enables regioselective heteroannulation ofo-bromoanilines with branched 1,3-dienes through ligand control. This approach provides regiodivergent access to 3-substituted indolines, showcasing excellent regioselectivity and reactivity across a range of functionalized substrates. To gain further insights into the origin of selectivity control, we employ a data-driven strategy, developing a linear regression model using calculated parameters for phosphorus ligands. This model identifies four key parameters governing regioselectivity in this transformation, paving the way for future methodology development. Additionally, density functional theory calculations elucidate key selectivity-determining transition structures along the reaction pathway, corroborating our experimental observations and establishing a solid foundation for future advancements in regioselective olefin difunctionalization reactions.
more »
« less
- Award ID(s):
- 2238081
- PAR ID:
- 10517754
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 15
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Herein, the synthesis of 1,2,3,4‐tetrasubstituted benzenoid rings, motifs found in pharmaceutical, agrochemical, and natural products, is described.[1]In the past, the regioselective syntheses of such compounds have been a significant challenge. This work reports a method using substituted arynes derived from aryl(Mes)iodonium salts to access a range of densely functionalized 1,2,3,4‐tetrasubstituted benzenoid rings. Significantly, it was found that halide substituents are compatible under these conditions, enabling post‐synthetic elaboration via palladium‐catalyzed coupling. This concise strategy is predicated on two regioselective events: 1) ortho‐ deprotonation of aryl(Mes)iodonium salts to generate a substituted aryne intermediate, and 2) regioselective trapping of said arynes, thereby improving previously reported reaction conditions to generate arynes at room temperature and in shorter reaction times. Density functional theory (DFT) computations and linear free energy relationship (LFER) analysis suggest the regioselectivity of deprotonation is influenced by both proximal and distal ring substituents on the aryne precursor. A competition experiment further reveals the role of arene substituents on relative reactivity of aryl(Mes)iodoniums as aryne precursors.more » « less
-
Abstract The production of olefins via on‐purpose dehydrogenation of alkanes allows for a more efficient, selective and lower cost alternative to processes such as steam cracking. Silica‐supported pincer‐iridium complexes of the form [(≡SiO−R4POCOP)Ir(CO)] (R4POCOP=κ3‐C6H3‐2,6‐(OPR2)2) are effective for acceptorless alkane dehydrogenation, and have been shown stable up to 300 °C. However, while solution‐phase analogues of such species have demonstrated high regioselectivity for terminal olefin production under transfer dehydrogenation conditions at or below 240 °C, in open systems at 300 °C, regioselectivity under acceptorless dehydrogenation conditions is consistently low. In this work, complexes [(≡SiO−tBu4POCOP)Ir(CO)] (1) and [(≡SiO−iPr4PCP)Ir(CO)] (2) were synthesized via immobilization of molecular precursors. These complexes were used for gas‐phase butane transfer dehydrogenation using increasingly sterically demanding olefins, resulting in observed selectivities of up to 77 %. The results indicate that the active site is conserved upon immobilization.more » « less
-
Abstract Herein, we developed the recyclable ligand‐free iridium (Ir)‐hydride based Ir0nanoparticles (NPs) for the first regioselective partial hydrogenation of PV‐substituted naphthalenes. Both the isolated and in situ generated NPs are catalytically active. A control nuclear magnetic resonance (NMR) study revealed the presence of metal‐surface‐bound hydrides, most likely formed from Ir0species. A control NMR study confirmed that hexafluoroisopropanol as a solvent was accountable for substrate activation via hydrogen bonding. High‐resolution transmission electron microscopy of the catalyst supports the formation of ultrasmall NPs, and X‐ray photoelectron spectroscopy confirmed the dominance of Ir0in the NPs. The catalytic activity of NPs is broad as showcased by highly regioselective aromatic ring reduction in various phosphine oxides or phosphonates. The study also showcased a novel pathway toward preparingbis(diphenylphosphino)‐5,5′,6,6′,7,7′,8,8′‐octahydro‐1,1′‐binaphthyl (H8‐BINAP) and its derivatives without losing enantioselectivity during catalytic events.more » « less
-
Abstract 3‐Aminopiperidines are a valuable motif present in small molecule pharmaceuticals and bioactive natural products. Synthesis of these moieties via olefin diamination would be an attractive approach, however significant challenges remain with regards to both regioselectivity and exogenous nucleophile scope. Herein, we report a metal‐free olefin diamination via a “heterocyclic group transfer“ (HGT) reaction of I(III)N‐HVI reagents, giving rise to 3‐aminopiperidines with high selectivity. The HGT strategy leverages heteroarenes as oxidatively masked amine nucleophiles, giving rise to (hetero)arylonium salt products which are isolated via simple trituration and provide a versatile handle for downstream diversification. This represents only the second6‐endoselective I(III)‐mediated diamination reaction and mechanistic studies indicate ring opening of an intermediate aziridinium ion is responsible for the6‐endoselectivity.more » « less
