Tandem gold(I)-catalyzed cyclization/electrophilic cyclopropanation of vinyl allenes

We have developed an expedient method for the synthesis of polycyclic compounds from propargyl acetates or vinyl allenes involving up to three Au(I)-catalyzed elemental steps: 3,3-rearrangement, metalla-Nazarov reaction, and electrophilic cyclopropanation. The reaction proceeds under very mild conditions and in short times. The mechanism has been studied by DFT computations.     

Gold(I)-catalyzed hydration of allenes

A gold(I) N-heterocyclic carbene complex catalyzes the intermolecular hydration of allenes to form allylic alcohols in modest yield with selective delivery of water to the terminal carbon atoms of the allenyl moiety.     

Gold(I)-catalyzed intramolecular hydroarylation of allenes

Gold(I) complexes react with 4-allenyl arenes in an exo fashion to furnish vinyl-substituted benzocycles. Phosphite gold(I) monocations were found to be optimal, and the catalyst was tolerant of ethers, esters, and pyrroles. Reactions proceeded in unpurified solvent at room temperature.     

Gold(I)-catalyzed hydroarylation of allenes with indoles

Reaction of a monosubstituted, 1,3-disubstituted, or tetrasubstituted allene with various indoles catalyzed by a 1:1 mixture of a gold(I) N-heterocyclic carbene complex and AgOTf at room temperature leads to hydroarylation with formation of 3-allyl-indoles in modest to good yield.     

New insight into Ni(II)-catalyzed cyclization reactions of propargylic compounds with soft nucleophiles: novel indenes formation

We have disclosed a very nice advance of nickel(II)-catalyzed carboannulation reactions. Highly substituted indene derivatives are readily prepared in moderate to excellent yields under very mild reaction conditions in air via a nickel(II)-catalyzed cyclization of propargylic compounds with soft nucleophiles.     

A novel atom-economic synthesis of functionalized imidazolidines through copper(I)-catalyzed domino three-component coupling and cyclization reactions

An interesting approach to functionalized imidazolidines is described. These compounds are obtained in a copper(I)-catalyzed domino three-component coupling and cyclization reaction involving two formaldehyde-derived imine units and a terminal alkyne. Alternatively, imidazolidines can be obtained from propargylamines and formaldehyde-derived imines. This strategy provides a straightforward and atom-economic pathway to construct imidazolidines with high yields and benefits from readily available starting materials, convenient one-pot operations.     

Water-triggered and gold(I)-catalyzed cascade addition/cyclization of terminal alkynes with ortho-alkynylaryl aldehyde

[reaction: see text] A highly efficient alkynylation-cyclization of terminal alkynes with ortho-alkynylaryl aldehydes leading to 1-alkynyl-1H-isochromenes was developed by using a gold-phosphine complex as catalyst in water. The reaction was dually promoted by an electron-donating phosphine ligand and water and was chelation-controlled.     

Gold(I)-catalyzed intramolecular enantioselective hydroarylation of allenes with indoles

Treatment of 2-allenyl indole 4 with a catalytic 1:2 mixture of [(S)-2]Au2Cl2 [(S)-2 = (S)-3,5-tBu-4-MeO-MeOBIPHEP] and AgBF4 in toluene at -10 degrees C for 17 h led to isolation of tetrahydrocarbazole 5 in 88% yield with 92% ee. The protocol was effective for the cyclization of terminally disubstituted allenes and for the formation of seven-membered rings.     

Copper(I)-catalyzed chlorine atom transfer radical cyclization reactions of unsaturated alpha-chloro beta-keto esters

Copper(I) chloride catalyzed chlorine atom transfer radical cyclization reactions of a series of olefinic alpha-chloro beta-keto esters were investigated. It was found that alpha-dichlorinated beta-keto esters were suitable substrates; the chlorine transfer mono or tandem radical cyclization reactions catalyzed by CuCl complex with bis(oxazoline) or bipyridine proceeded smoothly in dichloroethane at room temperature or 80 degrees C, providing cyclic and bicyclic compounds in moderate to high yield. [reaction: see text]     

Rh(I)-catalyzed carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids leading to indenones

The Rh-catalyzed reaction of alkynes with 2-bromophenylboronic acids involves carbonylative cyclization to give indenones. The key steps in the reaction involve the addition of an arylrhodium(I) species to an alkyne and the oxidative addition of C-Br bonds on the adjacent phenyl ring to give vinylrhodium(I) species II. The regioselectivity depends on both the electronic and the steric nature of the substituents on the alkynes. A bulky group and an electron-withdrawing group favor the -position of indenones. In the case of silyl- or ester-substituted alkynes, the regioselectivity is extremely high. The selectivity increases in the order SiMe3 > COOR > aryl > alkyl. The reaction of norbornene with 2-bromophenylboronic acids under 1 atm of CO gives the corresponding indanone derivative. The reaction of alkynes with 2-bromophenylboronic acids under nitrogen gives naphthalene derivatives, in which two molecules of alkynes are incorporated. A vinylrhodium complex similar to II can also be generated by a different route by employing 2-bromophenyl(trimethylsilyl)acetylene and arylboronic acids in the presence of Rh(I) complex as the catalyst, resulting in the formation of indenones. The reaction of 1-(2-bromophenyl)-hept-2-yn-1-one with PhB(OH)2 in the presence of Rh(I) complex also resulted in carbonylative cyclization to give an indan-1,3-dione derivative.     

Gold(I)-catalyzed intermolecular hydroarylation of allenes with nucleophilic arenes: scope and limitations

The addition of nucleophilic methoxyarenes to allenes proceeds at room temperature in dichloromethane with a catalytic amount of phosphite-gold(I) precatalyst and silver additive. The addition is regioselective for the allene terminus, and generates E-allylation products without the need for prefunctionalization of the synthons as organometallics or allyl bromides. Coordinating heteroaromatics and sterically hindered allenes do not participate in the reaction.     

Gold(I)-catalyzed cascade cyclization reaction: highly regio- and diastereoselective intermolecular addition of water and alcohols to epoxy alkynes

We have developed a novel access to ketal skeletons through a highly regio- and diastereoselective intermolecular addition of water and alcohols to alkynyl epoxides catalyzed by gold(I). This procedure involves a domino three-membered ring-opening, 6-exo-cycloisomerization, and subsequent intra- or intermolecular nucleophilic addition to a double-bond sequence.     

Copper(I)-catalyzed synthesis of 3,3-disubstituted isoindolin-1-ones from enamides via cascade radical addition and cyclization

Copper(I) catalyzed radical benzylation and cyclization reaction of tertiary enamides was investigated and 3,3-disubstituted N-Alkyl isoindolin-1-ones were obtained in moderate to good yields. In this reaction, two new C–C bonds were formed in one step with high atom economy. Possible reaction pathway for the formation of the products was also discussed in this paper.     

Regiocontrolled gold(I)-catalyzed cyclization reactions of N-(3-iodoprop-2-ynyl)-N-tosylanilines

The gold(I)-catalyzed cyclization reactions of N-(3-Iodoprop-2-ynyl)-N-tosylaniline derivatives afford iodinated 1,2-dihydroquinoline derivatives. Two regioisomer products are obtained, one derived from direct cyclization and other involving concomitant 1,2-iodo migration. The ratio of these two products can be modulated by a proper ancillary ligand in the gold catalyst.