General Methods. Reactions were performed under a nitrogen atmosphere employing standard Schlenk and/or drybox techniques unless specified otherwise. NMR were obtained on a Varian spectrometer operating at 400 MHz for 1 H, 202 MHz for 31 P, and 100 MHz for 13 C in CDCl 3 at 25 ¡C unless stated otherwise. IR spectra were obtained on a Nicolet Avatar 360-FT IR spectrometer. Gas chromatography was performed on a HP 5890 gas chromatograph equipped with a 25 m polydimethylsiloxane capillary column. Column chromatography was performed employing 230-450 mesh silica gel (Sorbent Technologies) unless noted otherwise; alternatively, chromatography employed 150 mesh activated aluminum oxide, neutral, Brockmann I (Aldrich). Thin layer chromatography (TLC) was performed on silica gel 60 F 254 . All compounds were isolated as colorless oils unless noted otherwise. Elemental analyses were performed by Complete Analysis Laboratories (Parsippany, NJ).1,4-Dioxane (anhydrous, Acros), triphenylphosphine (Fluka), and [PtCl 2 (C 2 H 4 )] 2(2) (Strem) were used as received. Tetrahydrofuran (THF) and diethyl ether were distilled from Na 0 /benzoquinone under N 2 , dichloromethane was distilled from CaH 2 under N 2 , and dioxane-d 8 was distilled from Na/K alloy under vacuum. [PtCl 2 (PPh 3 )] 2 (4) was synthesized employing a published procedure. S1 All other reagents were purchased from major chemical suppliers and were used as received.

Reaction of benzyl (2,2-diphenyl-4,5-hexadienyl)carbamate (4) with a catalytic 1:1 mixture of Au[P(t-Bu)2(o-biphenyl)]Cl (2) and AgOTf (5 mol %) in dioxane at 25 degrees C for 45 min led to isolation of benzyl 4,4-diphenyl-2-vinylpyrrolidine-1-carboxylate (5) in 95% yield. The Au(I)-catalyzed intramolecular hydroamination of N-allenyl carbamates tolerated substitution at the alkyl and allenyl carbon atoms and was effective for the formation of piperidine derivatives. gamma-Hydroxy and delta-hydroxy allenes also underwent Au-catalyzed intramolecular hydroalkoxylation within minutes at room temperature to form the corresponding oxygen heterocycles in good yield with high exo-selectivity. 2-Allenyl indoles underwent Au-catalyzed intramolecular hydroarylation within minutes at room temperature to form 4-vinyl tetrahydrocarbazoles in good yield. Au-catalyzed cyclization of N-allenyl carbamates, allenyl alcohols, and 2-allenyl indoles that possessed an axially chiral allenyl moiety occurred with transfer of chirality from the allenyl moiety to the newly formed stereogenic tetrahedral carbon atom.

The development of general and efficient methods for the addition of an N–H bond across a C–C multiple bond (hydroamination) represents a significant challenge in both organic synthesis and homogeneous catalysis. Although a diverse range of transition‐metal complexes have been employed as catalysts for hydroamination, examples of gold‐catalyzed hydroamination were exceedingly rare prior to 2001. However, over the past five years gold complexes have been applied as catalysts for a number of selective organic transformations including the hydroamination of unactivated alkenes, alkynes, allenes, and 1,3‐dienes. This Microreview provides a brief overview of the gold‐catalyzed hydroamination of C–C multiple bonds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The use of gold(I) complexes as catalysts for organic transformations has become increasingly common over the past decade, leading to the development of a number of useful carbon-carbon and carbon-heteroatom bond-forming processes. In contrast, enantioselective catalysis employing gold(I) complexes was, until recently, exceedingly rare, due in large part to the pronounced tendency of gold(I) to form linear, two-coordinate complexes. However, new approaches and strategies have emerged over the past two years, leading to the development of a number of effective gold(I)-catalyzed enantioselective transformations, most notably the enantioselective hydrofunctionalization of allenes. Outlined herein is an overview of enantioselective gold(I) catalysis since 2005.

The intermolecular hydroamination of unactivated alkenes remains an important, unsolved challenge in catalysis.1 Hydroamination has been realized with alkali metal amides,2 lanthanide metallocene complexes,3 or acidic zeolites,4 but these approaches suffer from a number of limitations, most notably poor functional group compatibility. Ru(II),5 Rh(III),6 and Pt(II)7 complexes catalyze the hydroamination of ethylene and, in one case, 1-hexene8 with carboxamides or alkyl or aryl amines, but these transformations require forcing conditions and are of extremely limited scope.9 Although electrophilic gold(I)-10 and platinum(II) triflate11 complexes have been reported to catalyze the intermolecular hydroamination of unactivated alkenes with sulfonamides, these transformations are catalyzed with equal or greater efficiency by Brønsted acids and the metal-catalyzed reactions display behavior consistent with Brønsted acid catalysis.12 -14 Given the challenges associated with the intermolecular hydroamination of unactivated alkenes, it is not surprising that the enantioselective intermolecular hydroamination of unactivated alkenes remains unknown.15 , 16 Here we report the Markovnikov-selective gold(I)-catalyzed hydroamination of ethylene and 1-alkenes with cyclic ureas and the unprecedented enantioselective hydroamination of unactivated 1-alkenes with up to 78% ee.We have recently reported the room temperature intramolecular hydroamination of γ-and δ-alkenyl ureas catalyzed by a mixture of a gold(I) N-heterocyclic carbene (NHC) complex and AgOTf. 17 The mild reaction conditions and the absence of an acid-catalyzed reaction pathway17 pointed to the potential development of a corresponding intermolecular process. However, attempts to realize the hydroamination of ethylene with acyclic ureas catalyzed by gold NHC complexes were uniformly unsuccessful. Conversely, cyclic ureas, employed in combination with a gold o-biphenyl phosphine precatalyst led to efficient hydroamination of ethylene. As an example, treatment of 1-methyl-imidazolidin-2-one (1) (0.4 M) with ethylene (120 psi) and a catalytic 1:1 mixture of (2a)AuCl [2a = P(t-Bu) 2 o-biphenyl] and AgOTf (5 mol %) in dioxane at 100 °C for 24 h led to isolation of 1-ethyl-3-methyl-imidazolidin-2-one (3) in 99% yield (Table 1, entry 1). In addition to 1, a number of cyclic ureas and 2-oxazolidinone reacted with ethylene at 100 °C to give the corresponding N-ethyl derivatives in good yield (Table 1, entries 5,6,7,10). 18 Extension of gold(I)-catalyzed hydroamination to include 1-alkenes was encouraging, but also revealed the limitations of the (2a)AuCl/AgOTf catalyst system. Gold(I)-catalyzed reaction of propene or 1-butene with cyclic ureas at 100 °C led to Markovnikov hydroamination in good yield with high regioselectivity, but extended reaction time and/or higher catalyst loading was rwidenho@chem.duke.edu .

Cationic, two-coordinate gold π complexes that contain a phosphine or N-heterocyclic supporting ligand have attracted considerable attention recently owing to the potential relevance of these species as intermediates in the gold-catalyzed functionalization of C-C multiple bonds. Although neutral two-coordinate gold π complexes have been known for over 40 years, examples of the cationic two-coordinate gold(I) π complexes germane to catalysis remained undocumented prior to 2006. This situation has changed dramatically in recent years and well-defined examples of two-coordinate, cationic gold π complexes containing alkene, alkyne, diene, allene, and enol ether ligands have been documented. This Minireview highlights this recent work with a focus on the structure, bonding, and ligand exchange behavior of these complexes.

Reaction of 2,2-diphenyl-4-penten-1-ol with a catalytic mixture of [PtCl2(H2C=CH2)]2 (1 mol %) and P(4-C6H4CF3)3 (2 mol %) at 70 degrees C for 24 h led to the isolation of 2-methyl-4,4-diphenyltetrahydrofuran in 78% yield. The platinum-catalyzed hydroalkoxylation of gamma-hydroxy olefins tolerated substitution at the alpha, beta, and gamma-carbon atoms and at the internal and cis and trans terminal olefinic positions. Platinum-catalyzed hydroalkoxylation tolerated a number of functional groups including pivaloate and acetate esters, amides, silyl and benzyl ethers, and pendant hydroxyl and olefinic groups. Pt-catalyzed olefin hydroalkylation was also applicable to the formation of fused- and spirobicyclic ethers and was effective for the hydroalkoxylation of delta-hydroxy olefins to form tetrahydropyran derivatives.

Cationic gold(I) complexes have recently emerged as effective catalysts for the functionalization of C-C multiple bonds. 1 With few exceptions, mechanisms involving outersphere attack of a nucleophile on a transient cationic gold π-complex have been invoked for these transformations. 1 However, although gold π-complexes have been known for over 40 years, examples of the cationic, two-coordinate gold(I) π-complexes germane to π-activation catalysis are exceedingly rare and monomeric gold(I) π-alkene complexes are unknown. [2][3][4][5] Echvarren 6 and Bertrand 7 have reported the X-ray crystal structures cationic, two coordinate gold π-arene complexes. Sadighi 8 and Bertrand 7 have reported monomeric, cationic gold(I) π-alkyne complexes, but high-resolution X-ray analysis has not been reported. 9 Toste has reported the X-ray crystal structures of multimeric, cationic, two-coordinate gold(I) π-alkyne and π-alkene complexes; however, no evidence supports the integrity of the gold(I) π-alkene bond in solution. 10 Here we report the syntheses, X-ray crystal structures, and solution behavior of monomeric, cationic, two-coordinate gold π-alkene complexes.Treatment of a methylene chloride suspension of (IPr)AuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine] and AgSbF 6 (1:1) with isobutylene at room temperature for 20 min led to isolation of [(IPr)Au(η 2 -H 2 C=CMe 2 )] + SbF 6 − (1a) in 98% yield as an air-and thermally-stable white solid that was characterized by NMR, MALDI-MS, combustion analysis, and X-ray crystallography (see below). Complexation of isobutylene to gold in solution was established by NMR, in particular by the large difference in the 13 C NMR shifts of the olefinic carbon atoms of bound [δ155.2 (s), 88.2 (t)] and free [δ142.4 (s), 110.5 (t)] isobutylene. The 1 J C=C coupling constant of the isobutylene ligand of the 13 C-isotopomer (IPr)Au(η 2 -H 2 13 C=CMe 2 ) (1a-13 C 1 ) ( 1 J C=C = 66 Hz) was diminished only slightly relative to free isobutylene ( 1 J C=C = 71 Hz), pointing to minimal deviation of the bound isobutylene from ideal sp 2 hydbridization. 11In addition to 1a, gold π-alkene complexes [(IPr)Au(η 2 -alkene)] + SbF 6 − [alkene = norbornene (1b), 2-methyl-2-butene (1c), methylenecyclohexane (1d), 2,3-dimethyl-2-butene (1e), cis-2-butene (1f), 1-hexene (1g), and 4-methylstyrene (1h)] were isolated in >80% yield and were fully characterized (Chart 1).Slow diffusion of hexane into a CH 2 Cl 2 solution of 1a at 4 °C gave colorless crystals of 1a·2CH 2 Cl 2 suitable for X-ray analysis ( Figure 1, Table 1). Complex 1a adopts a slightly distorted linear conformation with a C (carbene) -Au-alkene (centroid) angle of 172 °. The C=C bond of the isobutylene is rotated 52 degrees out of the carbene N-C-N plane, which positions E-mail: rwidenho@chem.duke.edu. Supporting Information Available: Experimental procedures, spectroscopic data, and X-ray crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. one isobutylene methyl group near the car...