Montmorillonite K-10-catalyzed intramolecular rearrangement of vinylidenecyclopropanes

A series of naphthalene, indene, and 6aH-benzo[c]fluorene derivatives are synthesized by intramolecular rearrangement of vinylidenecyclopropanes using a heterogeneous solid acid catalyst, montmorillonite K-10, under mild reaction conditions in good to excellent yields. The solid acidic catalyst, montmorillonite K-10, can be recovered and reused.     

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 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 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 intramolecular hydroamination of alkyne with trichloroacetimidates

[reaction: see text] A study on the gold (I)-catalyzed intramolecular hydroamination of trichloroacetimidates derived from propargyl and homopropargyl alcohols is described. In the presence of 2-5 mol % of cationic Au(I) complex, a variety of trichloroacetimidates undergo efficient hydroamination under an exceptionally mild condition. An orthogonality of the current catalytic protocol with those using a stoichiometric electrophile as well as a preliminary synthetic application as a stable precursor of 2-acylamino-1,3-diene has been demonstrated.     

Gold(I)-catalyzed intramolecular hydroamination of unactivated alkenes with carboxamides

N-Alkenyl carboxamides undergo gold-catalyzed intramolecular exo-hydroamination to form nitrogen heterocycles in excellent yield.     

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.     

Gold(I)-catalyzed intramolecular amination of allylic alcohols with alkylamines

A 1:1 mixture of (1)AuCl [1 = P(t-Bu)(2)o-biphenyl] and AgSbF(6) catalyzes the intramolecular amination of allylic alcohols with alkylamines to form substituted pyrrolidine and piperidine derivatives. Gold(I)-catalyzed cyclization of (R,Z)-8-(N-benzylamino)-3-octen-2-ol (96% ee, 95% de) led to isolation of (R,E)-1-benzyl-2-(1-propenyl)piperidine in 99% yield with 96% ee, consistent with the net syn addition of the amine relative to the departing hydroxyl group.     

Gold(I)-catalyzed intramolecular hydroamination and ring-opening of sulfonamide-substituted 2-(arylmethylene)cyclopropylcarbinols

An interesting gold(I)-catalyzed intramolecular hydroamination and ring-opening of sulfonamide-substituted 2-(arylmethylene)cyclopropylcarbinols has been described in this context. A variety of 4-substituted isoxazolidine derivatives were obtained in good to high yields through a highly regioselective cleavage of a carbon-carbon single bond in the cyclopropane.     

Gold(I)-catalyzed rearrangement of aryl alkynylaziridines to spiro[isochroman-4,2'-pyrrolines

Alkynylaziridines carrying an aryl group could be efficiently converted to spiro[isochroman-4,2'-pyrrolines] with gold salts as catalysts. This new rearrangement involved a Friedel-Crafts type intramolecular reaction followed by cyclization of the aminoallene intermediate, both initiated by the dual σ and π Lewis acidities of gold.     

Gold(I)-catalyzed rearrangement of alkynyloxiranes: a mild access to divinyl ketones

Acyloxylated divinyl ketones are conveniently formed by a new gold(I)-catalyzed rearrangement of (3-acyloxyprop-1-ynyl)oxiranes.     

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.