Regioselective and Chemoselective Reduction of Naphthols Using Hydrosilane in Methanol: Synthesis of the 5,6,7,8-Tetrahydronaphthol Core

Ligand-Free Ultrasmall Recyclable Iridium(0) Nanoparticles for Regioselective Aromatic Hydrogenation of Phosphine Oxide Scaffolds: An Easy Access to New Phosphine Ligands

Herein, we developed the recyclable ligand-free iridium (Ir)-hydride based Ir0 nanoparticles (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 Ir0 species. 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 Ir0 in 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 preparing bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (H8 -BINAP) and its derivatives without losing enantioselectivity during catalytic events.

Merging Hydrogen Atom Transfer and Halogen Atom Transfer for Iodide-Catalyzed Radical Reductive Cyclization of 1,6-Enynes

Described herein is the development of a metal-free iodide-catalyzed radical reductive cyclization of 1,6-enynes. A strategy involving in situ iodination/radical cyclization/silyl radical-mediated halogen atom transfer/hydrogen atom transfer for the synthesis of functionalized pyrrolidines has been proposed. Using this halogen-atom abstraction protocol, 1,6-enynes with various vinyl halides including inert fluorides, chlorides, and reactive bromides could be transformed into substituted pyrroles via a multistep radical isomerization process.

A mild and practical method for deprotection of aryl methyl/benzyl/allyl ethers with HPPh2 and tBuOK

A general method for the demethylation, debenzylation, and deallylation of aryl ethers using HPPh₂ and ^tBuOK is reported. The reaction features mild and metal-free reaction conditions, broad substrate scope, good functional group compatibility, and high chemical selectivity towards aryl ethers over aliphatic structures. Notably, this approach is competent to selectively deprotect the allyl or benzyl group, making it a general and practical method in organic synthesis.

Mild and Selective Rhodium-Catalyzed Transfer Hydrogenation of Functionalized Arenes

Diboron-mediated rhodium-catalyzed transfer hydrogenation of functionalized arenes is reported. In addition to good functional group tolerance, the reaction features operational simplicity and controllable chemoselectivity. The general applicability of this procedure is demonstrated by the selective hydrogenation of a range of arenes, including functionalized benzenes, biphenyls, and polyaromatics.

Atypical Dearomative Spirocyclization of β-Naphthols with Diazoacetamides Using a Silver Catalyst

A chemoselective dearomatization of the less reactive benzenoid unit in β-naphthol was developed. Spirocyclization with a reductant constructs a pivotal structure for drug candidates. One-pot oxidative conversion enabled the tandem dearomatization of β-naphthol, producing conjugated tetraenone variants. The potential utility of the product as an F^--selective anion sensor was also demonstrated. Theoretical studies revealed the intermediacy of silver-carbenoid species leading to chemoselective spirocyclization over arene cyclopropanation.

gem-Dichlorocyclopropanation of Dicarbonyl Derivatives

A novel methodology for the 1,1-dichlorocyclopropanation of dicarbonyl conjugated olefins was described. The developed protocol is simple and uses readily accessible starting materials, allowing the isolation of the desired adducts in moderate to excellent yields (up to 99 %). Furthermore, the reaction tolerated scale up to the gram scale; thus highlighting the synthetic potential of this transformation. Control experiments and DFT studies revealed that the reaction proceeded through a Michael-initiated ring-closure process, in which reaction temperature played a crucial role. Finally, these gem-dichlorocyclopropanes were also employed in the preparation of a trisubstituted naphthyl derivative and a diastereoselective reduction was also demonstrated.

Selective Arene Hydrogenation for Direct Access to Saturated Carbo- and Heterocycles

Arene hydrogenation provides direct access to saturated carbo- and heterocycles and thus its strategic application may be used to shorten synthetic routes. This powerful transformation is widely applied in industry and is expected to facilitate major breakthroughs in the applied sciences. The ability to overcome aromaticity while controlling diastereo-, enantio-, and chemoselectivity is central to the use of hydrogenation in the preparation of complex molecules. In general, the hydrogenation of multisubstituted arenes yields predominantly the cis isomer. Enantiocontrol is imparted by chiral auxiliaries, Brønsted acids, or transition-metal catalysts. Recent studies have demonstrated that highly chemoselective transformations are possible. Such methods and the underlying strategies are reviewed herein, with an emphasis on synthetically useful examples that employ readily available catalysts.