Gold-Catalyzed Enantioselective Annulations

Divergent access to N-hydroxypyrroles and isoxazoles via the gold(i)- or Brønsted acid-catalysed regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes

The divergent regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes by a suitable choice of a gold(i) or a Brønsted acid catalyst, leading to 4-trifluoromethyl-N-hydroxypyrroles or 4-trifluoromethyl-5-alkylisoxazoles was developed. In order to avoid the tedious separation of unstable N-(2-trifluoromethyl-3-alkynyl) oximes, an easy two-step, one-pot synthesis of 4-trifluoromethyl-5-alkylisoxazoles was realized via the sequential oxidation of the corresponding hydroxylamines and subsequent treatment with the reductant, sodium thiosulfate (Na₂S₂O₃)_. This two-step, one-pot procedure is a complementary method for the synthesis of 4-trifluoromethyl-5-alkylisoxazole from those unstable N-(2-trifluoromethyl-3-alkynyl) oximes.

Gold-Catalyzed Divergent Ring-Closing Modes of Indole-Tethered Amino Allenynes

Indole-tethered amino allenynes were chemodivergently cyclized for the controlled preparation of fused polycyclic indoles using gold catalysis. Double cyclization of terminal allenynes afforded hexacyclic 15 H-indolo[1,2,3-de]quinolino[3,2,1-ij]quinoxalines, in which allenynes bearing a substituted alkyne at the terminal end generated 12,13-dihydro-7 H-indolo[3,2-c]acridines, which are 5-membered cyclized adducts. Density functional theory calculations were performed to shed light on this difference in reactivity.

Ruthenium–indolizinone complexes as a new class of metalated heterocyclic compounds: insight into unconventional alkyne activation pathways, revelation of unexpected electronic properties and exploration of medicinal application

The first examples of metal–indolizinone complexes prepared by Ru-assisted activation of pyridine-tethered alkynes exhibit moderate cytotoxicity against several human cancer cell lines.

Synthesis of indolizine derivatives containing eight-membered rings via a gold-catalyzed two-fold hydroarylation of diynes

A novel strategy for a gold(i)-catalyzed synthesis of indolizine derivatives containing eight-membered rings has been developed, which may have potential usefulness as blue or green OLEDs.

Au(i)-Catalyzed expeditious access to naphtho[2,3-c]furan-1(3-H)-ones from readily available propargylic ynoates

Gold(i)-catalyzed facile construction of naphtho[2,3-c]furan-1(3-H)-ones from readily available propargylic ynoates has been developed.

Gold-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes

A gold(i)-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes has been developed, providing facile access to functionalized polycyclic and spiropolycyclic products based on the use of gold(i) catalysts.

Infrared Spectroscopy of Au+(CH4) n Complexes and Vibrationally-Enhanced C-H Activation Reactions

A combined spectroscopic and computational study of gas-phase Au⁺(CH₄)_n (n = 3–8) complexes reveals a strongly-bound linear Au⁺(CH₄)₂ core structure to which up to four additional ligands bind in a secondary coordination shell. Infrared resonance-enhanced photodissociation spectroscopy in the region of the CH₄a₁ and t₂ fundamental transitions reveals essentially free internal rotation of the core ligands about the H₄C–Au⁺–CH₄ axis, with sharp spectral features assigned by comparison with spectral simulations based on density functional theory. In separate experiments, vibrationally-enhanced dehydrogenation is observed when the t₂ vibrational normal mode in methane is excited prior to complexation. Clear infrared-induced enhancement is observed in the mass spectrum for peaks corresponding 4u below the mass of the Au⁺(CH₄)_n=2,3 complexes corresponding, presumably, to the loss of two H₂ molecules.

Enantioselective Synthesis of Cyclobutenes by Intermolecular [2+2] Cycloaddition with Non-C2 Symmetric Digold Catalysts

The enantioselective intermolecular gold(I)-catalyzed [2+2] cycloaddition of terminal alkynes and alkenes has been achieved using non-C2-chiral Josiphos digold(I) complexes as catalysts, by the formation of the monocationic complex. This new approach has been applied to the enantioselective total synthesis of rumphellaone A.

Parameterization of Acyclic Diaminocarbene Ligands Applied to a Gold(I)-Catalyzed Enantioselective Tandem Rearrangement/Cyclization

Computed descriptors for acyclic diaminocarbene ligands are developed in the context of a gold catalyzed enantioselective tandem [3,3]-sigmatropic rearrangement-[2+2]-cyclization. Surrogate structures enable the rapid identification of parameters that reveal mechanistic characteristics. The observed selectivity trends are validated in a robust multivariate analysis facilitating the development of a highly enantioselective process.

Substrate Specific Silver(I)-Catalyzed Cycloisomerization of Diene Involving Alkyl Rearrangements: Syntheses of 1,2,5,6-Tetrahydrocuminic Acid, p-Menth-3-en-7-ol, and p-Menth-3-en-7-al

The novel cationic Ag(I)-catalyzed cycloisomerization, which is associated with alkyl rearrangements, from dimethyl 2-allyl-2-prenylmalonate (1) to dimethyl 4-isopropylcyclohex-3-ene-1,1-dicarboxylate (2) has been developed. Derivatization from the diester 2 into the diol 3 and its X-ray crystallographic analysis determined the structure. The mechanisms of the novel reaction were investigated by isotopic experiments, which supported the unusual alkyl shifts. In addition, the product 2 was used for the total syntheses of three natural products, 1,2,5,6-tetrahydrocuminic acid (12), p-menth-3-en-7-ol (13), and p-menth-3-en-7-al (14) in short steps.

Well-Defined Chiral Gold(III) Complex Catalyzed Direct Enantioconvergent Kinetic Resolution of 1,5-Enynes

The development of a gold(III) catalyzed direct enantioconvergent 1,5-enyne cycloisomerization and kinetic resolution reaction is described. The transformation results in highly enantioenriched bicyclo[3.1.0]hexenes at all levels of conversion, with no racemization or symmetrization taking place during the course of the reaction, and simultaneously affords optically enriched 1,5-enynes. This report marks the first highly enantioselective transformation catalyzed by a well-defined cationic gold(III) catalyst and demonstrates the unique potential of gold(III) complexes in enantioselective catalysis.

Enantioselective gold(i)-catalyzed rearrangement of cyclopropyl-substituted 1,6-enynes into 2-oxocyclobutyl-cyclopentanes

A gold(i)-catalyzed cycloisomerization/ring expansion sequence allows the highly enantioselective synthesis of 2-oxocyclobutylcyclopentane derivatives from cyclopropyl-substituted enynes (up to 99% ee).

Broad scope gold(i)-catalysed polyenyne cyclisations for the formation of up to four carbon–carbon bonds

The polycyclisation of polyeneynes catalyzed by gold(i) has been extended for the first time to the simultaneous formation of up to four carbon–carbon bonds, leading to steroid-like molecules with high stereoselectivity in a single step with low catalyst loadings.