Dual Photoredox/Gold Catalysis Arylative Cyclization of <i>o</i>‑Alkynylphenols with Aryldiazonium Salts: A Flexible Synthesis of Benzofurans

A new method for the arylative cyclization of <i>o</i>-alkynylphenols with aryldiazonium salts via dual photoredox/gold catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives and offers an efficient approach to benzofuran derivatives. The scope of the transformation is wide, and the limitations are discussed. The reaction is proposed to proceed through a photoredox-promoted generation of a vinylgold­(III) intermediate that undergoes reductive elimination to provide the heterocyclic coupling adduct

3‑Sulfonylindoles via Gold- or Silver-Catalyzed Cyclization1,3-Sulfonyl Migration Sequences under Visible Light Irradiation

A pathway for the synthesis of 3-sulfonylindoles has been devised. Upon blue LED irradiation, in the presence of a gold(I) or a silver(I) salt, ortho-alkynyl N-sulfonyl precursors readily undergo a 5-endo-dig cyclization concomitant with a 1,3-sulfonyl migration. While the gold-catalyzed reaction takes place in photocatalyst-free conditions, an iridium photocatalyst (Ir[dF(CF3)ppy]2(dtbbpy)PF6) is necessary with silver catalysis. Mechanistic studies featuring the generation of a sulfonyl radical support this dichotomy

Rearrangements of <i>N</i>‑Acyl Isothioureas. Alternate Access to Acylguanidines from Cyanamides

We report a tin-free one-pot radical approach to the synthesis of <i>N</i>-acyl isothioureas and acylguanidines from <i>N</i>-acyl cyanamides. Photoactivated reduction of aromatic disulfides in the presence of Hünig’s base results in hydrothiolation of the cyanamide moiety, followed by spontaneous 1,3-migration of the acyl group. Onward reaction of the isothioureas obtained with amines led to the corresponding <i>N</i>-acylguanidines, where the acyl group is attached to the nitrogen atom formerly at the cyano-end of the starting material

Double-Stereodifferentiation in Rhodium-Catalyzed [2 + 2 + 2] Cycloaddition: Chiral Ligand/Chiral Counterion Matched Pair

The first enantioselective metal-catalyzed [2 + 2 + 2] cycloaddition involving a double asymmetric induction has been devised. It relies on the use of an in situ generated chiral cationic rhodium­(I) catalyst with a matched chiral ligand/chiral counterion pair. Careful optimization of the catalytic system, as well as of the reaction conditions, led to atroposelective [2 + 2 + 2] pyridone cycloadducts with high ee’s up to 96%. This strategy outperformed those previously described involving a chiral ligand only or a chiral counterion only

Gold-Catalyzed Polymerization Based on Carbene Polycyclopropanation

The first polymerization exploiting the carbenic reactivity of homogeneous gold catalysis has been devised. In the presence of a gold catalyst, monomers incorporating both a propargylic ester and an alkene moiety polymerized through a metallocarbene generation/cyclopropanation sequence to afford the corresponding macromolecules. This approach constitutes an unprecedented example of cyclopropanation-based polymerization and allows access to original macromolecule skeletons

Gold Compounds Anchored to a Metalated Arene Scaffold: Synthesis, X‑ray Molecular Structures, and Cycloisomerization of Enyne

A novel series of π-complexes of phosphino ligands, [Cp*Ru­(η^<i>6</i>-arene-PAr₂)]­[OTf], has been prepared in which the diarylphosphine unit is attached to a metalated π-arene scaffold. These organometallic phosphino ligands display either an electron-donating methyl group (−PAr₂ = −P­(<i>p</i>-tol)₂) or electron-withdrawing trifluoromethyl group (−PAr₂ = −P­(<i>p</i>-C₆H₄CF₃)₂). This unique class of metallo ligands was converted to heterodinuclear gold complexes upon treatment with [AuCl­(tht)]. The molecular structures of [Cp*Ru­(η⁶-<i>p</i>-CH₃C₆H₄-P­(<i>p</i>-tol)₂-Au-Cl)]­[OTf] and [Cp*Ru­(η^<i>6</i>-C₆H₅-P­(<i>p</i>-C₆H₄CF₃)₂)-Au-Cl]­[OTf] were ascertained by single-crystal X-ray diffraction. A comparative study of these structures with that of [Cp*Ru­(η^<i>6</i>-C₆H₅-PPh₂-Au-Cl)]­[OTf] previously reported revealed important information about the electronic nature of the gold center when it is bonded to a −PPh₂, −P­(<i>p</i>-tol)₂, or −P­(<i>p</i>-C₆H₄CF₃)₂ metallo ligand. DFT computations also shed light on the effect of [Cp*Ru⁺] coordination to [AuCl­(PAr₃)] precatalysts. Several complexes of the family with electron-donating and -withdrawing groups were evaluated toward cycloisomerization reactions of a classical <i>N</i>-tethered 1,6-enyne. These results are presented and discussed