Gold(I)-catalyzed synthesis of highly substituted furans

Cationic triphenylphosphinegold(I) complexes are excellent catalysts for a cascade reaction of propargyl-Claisen rearrangement and heterocyclization to synthesize tri- and tetrasubstituted furans. Starting from easily accessed propargyl vinyl ethers, the furans are obtained in 72-99% yield. [reaction: see text]     

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 asymmetric synthesis of planar chiral arene chromium complexes

Gold(I)-catalyzed asymmetric cyclization of 1,3-dihydroxymethyl-2-alkynylbenzene chromium complexes gave planar chiral isochromene chromium complexes with high enantioselectivity. Enantiomeric excess of the cyclization products was largely affected by a combination of axially chiral diphosphine(AuCl)(2) precatalysts and silver salts. A system of segphos(AuCl)(2) with AgBF(4) resulted in the formation of the corresponding antipode.     

Gold(I)-catalyzed propargyl Claisen rearrangement

Homoallenic alcohols are prepared from propargyl vinyl ethers using a trinuclear gold(I)-oxo complex, [(Ph3PAu)3O]BF4, as a catalyst for propargyl Claisen rearrangement at room temperature. The gold(I)-catalyzed reaction is effective for a diverse collection of propargyl vinyl ethers, including substrates containing aryl and alkyl groups at the propargylic position, and hydrogen, aryl, and alkyl substituents at the alkyne terminus. Tertiary propargyl vinyl ethers can be employed in the reaction, at slightly elevated temperatures, to afford tetrasubstituted allenes. Importantly, the rearrangement of 1,2-disubstituted vinyl ethers proceeds with excellent diastereoselectivity, and the rearrangement of chiral nonracemic propargyl vinyl ethers proceeds with excellent chirality transfer to furnish enantioenriched allenes.     

Gold(I)-catalyzed stereoselective olefin cyclopropanation

A triphenylphosphinegold(I)-catalyzed cyclopropanation of olefins using propargyl esters as gold(I)-carbene precursors is reported. This reaction provided the basis for the use of a DTBM-SEGPHOS gold(I) complex as a catalyst in the enantioselective (up to 94% ee) preparation of vinyl cyclopropanes with high cis-selectivity.     

Gold(I)-catalyzed glycosidation of 1,2-anhydrosugars

Being able to increase the yield by >20% compared to the conventional use of anhydrous zinc chloride (>1 equiv) as a promoter, Ph 3PAuOTf is disclosed to be a superior catalyst for the well-established glycosylation reaction with 1,2-anhydrosugars as donors.     

Gold(I)-catalyzed intramolecular rearrangement of vinylidenecyclopropanes

Vinylidenecyclopropanes 1 can undergo intramolecular rearrangement to give the corresponding functionalized 1,2-dihydronaphthalenes in the presence of gold catalyst under mild conditions. A plausible rearrangement mechanism has been proposed on the basis of control experiments.     

Gold(I)-catalyzed synthesis of 1,5-benzodiazepines directly from o-phenylenediamines and alkynes

A unique gold(I)-catalyzed highly atom-economic synthesis of 1,5-benzodiazepines directly from o-phenylenediamines and alkynes has been achieved for the first time.     

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 intramolecular cyclopropanation of dienynes

Gold(I) complexes are the most active catalysts for the biscyclopropanation of dienynes to form tetracyclic compounds. PtII and ZnII are also able to promote the biscyclopropanation, although less efficiently. The configurations obtained in all cases with the use of gold(I) catalysts can be explained by the pathway proceeding through anti cyclopropyl gold carbenes. Similar intermediates are most probably involved in reactions catalyzed by RuII and PtII. Two different cyclopropanation pathways have been found; they depend on the structures of the cyclopropyl gold carbenes (anti or syn) and the relative arrangements of the metal carbenes and the alkenes.     

Gold(I)-catalyzed arylmethylation of terminal alkynes

AuCl/AgOTf catalyzes the reaction of terminal alkynes with aryl trichloroacetimidate to afford arylmethylation products in moderate to good yields.     

Gold(I)-catalyzed intramolecular acetylenic Schmidt reaction

Substituted pyrroles were prepared by a gold(I)-catalyzed acetylenic Schmidt reaction of homopropargyl azides. The reaction allows for regiospecific substitution at each position of the pyrrole ring under mild conditions. A mechanism in which azides serve as nucleophiles toward gold(I)-activated alkynes with subsequent gold(I)-aided expulsion of dinitrogen is proposed.     

Gold(I)-catalyzed enantioselective hydroamination of N-allenyl carbamates

Treatment of the N-4,5-hexadienyl carbamate 2a with a catalytic 1:2 mixture of [(S)-1]Au2Cl2 [(S)-1 = (S)-3,5-t-Bu-4-MeO-MeOBIPHEP] and AgClO4 in m-xylene at -40 degrees C for 24 h led to isolation of 2-vinylpyrrolidine 3a in 97% yield with 81% ee. Gold(I)-catalyzed enantioselective hydroamination was effective for a number of carbamate groups and tolerated terminal disubstitutution of the allenyl moiety.