Gold(I)‐Catalysed Cycloisomerisation of 1,6‐Cyclopropene‐enes

The gold(I)‐catalysed cycloisomerisation of appropriately substituted 1,6‐cyclopropene‐enes proceeds through regioselective electrophilic ring opening of the three‐membered ring to generate an alkenyl gold carbenoid that achieves the intramolecular cyclopropanation of the remote olefin. This strategy allows straightforward, highly efficient and diastereoselective access to a variety of substituted 3‐oxa‐ and 3‐azabicyclo[4.1.0]heptanes, as well as to bicyclo[4.1.0]heptan‐3‐ol derivatives. Since the isopropylidene group in the resulting cycloisomerisation products can be subjected to ozonolysis, 3,3‐dimethylcyclopropenes behave as interesting surrogates for α‐diazoketones.     

Gold(III) π‐Allyl Complexes

Gold(III) π‐complexes have been authenticated recently with alkenes, alkynes, and arenes. The key importance of Pd^II π‐allyl complexes in organometallic chemistry (Tsuji–Trost reaction) prompted us to explore gold(III) π‐allyl complexes, which have remained elusive so far. The (P,C)Au^III(allyl) and (methallyl) complexes 3 and 3′ were readily prepared and isolated as thermally and air‐stable solids. Spectroscopic and crystallographic analyses combined with detailed DFT calculations support tight quasi‐symmetric η³‐coordination of the allyl moiety. The π‐allyl gold(III) complexes are activated towards nucleophilic additions, as substantiated with β‐diketo enolates.     

Divergent Gold(I)‐Catalyzed Skeletal Rearrangements of 1,7‐Enynes

The gold(I) complex catalyzed cycloisomerization and skeletal rearrangement of 1,n‐enynes (n=5–7) is a powerful methodology for the efficient synthesis of complex molecular architectures. In contrast to 1,6‐enynes, readily accessible homologous 1,7‐enynes are largely unexplored in such transformations. Here, the divergent skeletal rearrangement of all‐carbon 1,7‐enynes by catalysis with a cationic gold(I) complex is reported. Depending on electronic and steric factors, differently substituted 1,7‐enynes react via different carbocations formed from a common gold carbene intermediate to yield on the one hand novel exocyclic allenes and on the other hand tricyclic hexahydro‐anthracenes through a novel dehydrogenative Diels–Alder reaction.     

Gold(I) ‐Nickel(II)‐4,4′‐bpy‐Phosphine Complexes: Synthesis and Multinuclear NMR Study

Silver triflate [AgOTf] assisted de‐bromination gives [Ni(dppm/dppe/(PPh₃)₂) (OTf)₂], which on reaction with 4,4′‐bpy and gold(I) phosphines in dichloromethane medium by the self assemble technique leads to [{(L)Ni}{(4,4‐bpy)Au(PPh₃)}₂](OTf)₄, ( 1,2,3 ) [{(L)Ni(4,4‐bpy)}₄](OTf)₈, ( 4,5,6 ) [L = dppm/dppe/(PPh₃)₂ = diphenyl phosphino‐methane, ‐ethane, bis‐triphenylphosphine, OSO₂CF₃ is the triflate anion]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. Ir spectra of the complexes show ‐C=C‐, ‐C=N‐, as well as phosphine stretching. The ¹H NMR spectra as well as ³¹P (¹H)NMR suggest solution stereochemistry, proton movement, and phosphorus proton interaction. Considering all the moieties, there are a lot of carbon atoms in the molecule reflected by the ¹³C NMR spectrum. In the ¹H‐¹H COSY spectrum of the present complexes and contour peaks in the ¹H^?13C HMQC spectrum, we assign the solution structure and stereoretentive transformation in each step.     

The Gold(I)‐Catalysed Protodecarboxylation Mechanism

A mechanistic study of the gold‐catalysed protodecarboxylation is described. Each reaction step has been investigated experimentally and computationally. More specifically, the activation parameters for the decarboxylation step have been determined through kinetic studies. Further experimental studies on the hydrolysis of the arylgold intermediate have revealed that the protodeauration can become competitive with the decarboxylation process at high conversions. This switch in rate‐limiting step has been shown to be pK_a‐dependent. These studies have been supported by DFT calculations and permit a better understanding of which prevalent features of the reaction mechanism account for the decarboxylation process.     

Gold(I)‐Catalyzed Cycloisomerizations and Alkoxycyclizations of ortho‐(Alkynyl)styrenes

Indenes and related polycyclic structures have been efficiently synthesized by gold(I)‐catalyzed cycloisomerizations of appropriate ortho‐(alkynyl)styrenes. Disubstitution at the terminal position of the olefin was demonstrated to be essential to obtain products originating from a formal 5‐endo‐dig cyclization. Interestingly, a complete switch in the selectivity of the cyclization of o‐(alkynyl)‐α‐methylstyrenes from 6‐endo to 5‐endo was observed by adding an alcohol to the reaction media. This allowed the synthesis of interesting indenes bearing an all‐carbon quaternary center at C1. Moreover, dihydrobenzo[a]fluorenes can be obtained from substrates bearing a secondary alkyl group at the β‐position of the styrene moiety by a tandem cycloisomerization/1,2‐hydride migration process. In addition, diverse polycyclic compounds were obtained by an intramolecular gold‐catalyzed alkoxycyclization of o‐(alkynyl)styrenes bearing a nucleophile in their structure. Finally, the use of a chiral gold complex allowed access to elusive chiral 1H‐indenes in good enantioselectivities.     

Investigation of the Reaction of Gold(III) with 2‐[2‐(4‐Dimethylamino‐Phenyl)‐Vinyl]‐1,3,3‐Trimethyl‐3H‐Indolium. Application for Determination of Gold

A new, simple, rapid, sensitive, efficient and low‐cost spectrophotometric procedure for the determination of gold was developed. The method is based on the reaction of [AuCl₄]^? with 2‐[2‐(4‐dimethylaminophenyl)‐vinyl]‐1,3,3‐trimethyl‐3H‐indolium reagent to form a colored ion associate extractable by various organic solvents. The molar absorptivity of the ion associates is in the range (5.7–9.2) × 10⁴ L mol^?1 cm^?1 depending on the extractant. Butyl acetate was chosen as the extractant. The optimum reaction conditions were established: pH 2–4, concentration of the dye reagent (0.8–1.5) × 10^?4 mol L^?1. The determination of gold is not hindered even by a 1000‐fold concentration of Ni and Co; a 500‐fold concentration of Pb and Zn; a 100‐fold concentration of Bi, Cu, Cd, Pt, Rh and Ru; or a 20‐fold concentration of Ag. The established method was applied to the determination of gold in model samples and enriched polymetallic ores.