Synthesis of indenyl ethers by gold(I)-catalyzed intramolecular carboalkoxylation of alkynes

The gold(I)-catalyzed carboalkoxylation of alkynes to form indanone derivatives from readily available ortho-acetylenic benzylic ethers is described. Importantly, the gold(I)-catalyzed rearrangement of enantioenriched benzylic ethers proceeds with chirality transfer, thus providing a practical method for the enantioselective synthesis of indenyl ethers.     

Gold(I)-catalyzed ring expansion of cyclopropanols and cyclobutanols

The rearrangement of 1-alkynyl cyclobutanols and cyclopropanols to alkylidene cycloalkanones catalyzed by cationic triarylphosphine gold(I) complexes is described. The reaction tolerates terminal alkynes as well as alkyl, aryl, and halo-substitution at the acetylenic position and stereoselectively provides a single olefin isomer. The gold(I)-catalyzed rearrangement is stereospecific with regard to substituents on the ring, thus providing a practical method for the stereoselective synthesis of highly substituted cyclopentanones from cyclopropanols. The reaction stereoselectively provides a single olefin isomer and is stereospecific with regard to substituents on the ring via sequential gold(I)-catalyzed ring expansion reactions.     

Gold(I)-catalyzed stereoselective formation of functionalized 2,5-dihydrofurans

[reaction: see text] A study concerning the gold(I)-catalyzed rearrangement of butynediol monobenzoates into functionalized 2,5-dihydrofurans is described. The mild reaction conditions employed allow the efficient and rapid stereoselective synthesis of a variety of 2,5-dihydrofurans via a sequence of two gold(I)-catalyzed isomerization steps.     

Synthesis of highly substituted pyrroles via a multimetal-catalyzed rearrangement-condensation-cyclization domino approach

[reaction: see text] In a convenient one-pot process, easily accessed propargyl vinyl ethers and aromatic amines are effectively converted into tetra- and pentasubstituted 5-methylpyrroles which can further be transformed into 5-formylpyrroles via IBX-mediated oxidation. The cascade reaction proceeds through a silver(I)-catalyzed propargyl-Claisen rearrangement, an amine condensation, and a gold(I)-catalyzed 5-exo-dig heterocyclization.     

Strategies for expanding structural diversity available from olefin isomerization-claisen rearrangement reactions

Boron-substituted di(allyl) ethers provide an efficient conduit for expanding the structural diversity available from olefin isomerization-Claisen rearrangement (ICR) reactions. Easily prepared allyl propargyl ethers undergo chemoselective Zr(IV)-catalyzed hydroboration to afford the boron-substituted ICR substrates. The boron-substituted allyl residue undergoes chemoselective Ir(I)-catalyzed olefin isomerization and in situ Claisen rearrangement to afford stereodefined beta-boryl aldehyde products. Functionalization of the C-B linkage by oxidation or Suzuki cross-coupling provides a route to Claisen adducts previously inaccessible from the ICR methodology.     

Synthesis of 2-cyclopentenones by gold(I)-catalyzed Rautenstrauch rearrangement

The rearrangement of 1-ethynyl-2-propenyl pivaloates to cyclopentenones catalyzed by cationic triphenylphosphinegold(I) complexes is described. The reaction tolerates both alkyl and aryl substitution at the acetylenic and olefinic positions. Importantly, the gold(I)-catalyzed rearrangement of enantioenriched propargyl pivaloates proceeds with excellent chirality transfer, thus providing a practical method for the enantioselective synthesis of cyclopentenones.     

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.     

Rh(I)-catalyzed allenic Pauson-Khand reaction: first construction of the bicyclo[6.3.0]undecadienone ring system

The Rh(I)-catalyzed Pauson-Khand reaction of allenynes afforded the bicyclo[6.3.0]undecadienones as well as their benzo and furo derivatives. In addition, a novel [RhCl(CO)₂]₂-catalyzed [2,3]-sigmatropic rearrangement of the sulfinic ester species of propargyl alcohols was developed.     

3-Halotetrahydropyran-4-one Derivatives from Homopropargyl Acetal

A gold(I)-catalyzed regioselective method for the preparation of 3-bromo/iodo-tetrahydropyran-4-one derivatives from homopropargyl acetal is reported. A one-pot procedure based on a gold(I)-catalyzed Petasis–Ferrier rearrangement/cyclization and subsequent electrophilic halogenation was developed. Corresponding hemiacetals were not suitable substrates for the formation of the 3-halo-pyran derivatives. The present transformation is a useful method to readily afford highly substituted 3-halo-tetrahydropyran-4-ones, which are suitable substrates in a variety of reactions in further synthesis.     

Gold(I)-catalyzed cycloisomerization of β-alkynylpropiolactones to substituted α-pyrones

Substituted α-pyrones were straightforwardly synthesized in good to excellent yields by a new gold(I)-catalyzed rearrangement of β-alkynylpropiolactones.     

Pd(II)-catalyzed aliphatic Claisen rearrangements of acyclic allyl vinyl ethers

Palladium (II)-catalyzed [3,3] sigmatropic rearrangement of acyclic allyl vinyl ethers delivers 2,3-anti disubstituted pentenal Claisen adducts with high diastereoselectivity. Reaction conditions for circumventing allyl vinyl ether cleavage that had previously plagued catalyzed rearrangement of α-unsubstituted vinyl ether substrates are described. Merging Pd(II) catalysis with the facile access to the Claisen substrates afforded by Ir(I)-catalyzed olefin isomerization provides an expedient procedure for realizing asymmetric anti-selective Claisen rearrangements.     

Unexpected cycloisomerizations of nonclassical carbocation intermediates in gold(I)-catalyzed homo-Rautenstrauch cyclizations

An unexpected gold(I)-catalyzed homo-Rautenstrauch rearrangement of 1-cyclopropyl propargylic esters to cyclohexenones is disclosed. This rearrangement represents new evidence for the recently discussed gold-stabilized nonclassical carbocation character of intermediates in gold catalysis. A mechanistic study proved partial chirality transfer from optically active propargyl acetates.     

Gold(I)-catalyzed unprecedented rearrangement reaction between 2-aminobenzaldehydes with propargyl amines: an expedient route to 3-aminoquinolines

Access to aminoquinolines: a gold(I)-catalyzed unprecedented rearrangement reaction between 2-aminobenzaldehydes with propargyl amine was studied. The study provided, for the first time, direct access to 3-aminoquinolines in one step starting from readily available starting materials. Elegantly designed experiments were employed to unravel the mechanism of this unprecedented rearrangement, which are corroborated by DFT calculations.     

Gold(I)-catalyzed rearrangement of alkynylaziridine indoles for the synthesis of spiro-tetrahydro-β-carbolines

Functionalized spiro-tetrahydro-β-carbolines were formed by an efficient gold(I)-catalyzed rearrangement reaction of alkynylaziridine indoles. The reaction involved a Friedel–Crafts type intramolecular reaction of alkynylaziridine indoles, following by hydroamination of aminoallene intermediate.     

Copper(I)-catalyzed cascade sulfonimidate to sulfonamide rearrangement: synthesis of imidazo[1,2-a][1,4]diazepin-7(6H)-one

A novel strategy of copper(I)-catalyzed cascade intramolecular nucleophilic attack on N-sulfonylketenimine followed by rearrangement of sulfonimidates to sulfonamides resulting in a library of substituted 8,9-dihydro-5H-imidazo[1,2-a][1,4]diazepin-7(6H)-ones has been developed.     

Stereoselective olefin isomerization leading to asymmetric quaternary carbon construction

Chemo- and stereoselective Ir(I)-catalyzed isomerization of 1,1-disubstituted and trisubstituted allylic ethers and in situ [3,3] sigmatropic rearrangement of the resulting allyl vinyl ethers provide for the highly stereoselective construction of quaternary carbon stereocenters. The olefin isomerization-Claisen rearrangement (ICR) sequence allows adjacent quaternary-tertiary stereocenter relationships to be established with excellent diastereoselection. Several complementary strategies for enantioselective quaternary carbon synthesis derive directly from the ICR reaction design.     

Regioselectivity switch: gold(i)-catalyzed oxidative rearrangement of propargyl alcohols to 1,3-diketones

The gold(I)-catalyzed oxidative rearrangement of propargyl alcohols provides an efficient and selective route to 1,3-diketones under mild conditions. Pyridine-N-oxides were used as external oxidants with, different from related substrates, no alkylidenecycloalkanones or oxetan-3-ones formed as side-products.     

Gold(I) catalyzed isomerization of 5-en-2-yn-1-yl acetates: an efficient access to acetoxy bicyclo[3.1.0]hexenes and 2-cycloalken-1-ones

The gold(I) catalyzed rearrangement of 5-en-2-yn-1-yl acetates into functionalized acetoxy bicyclo[3.1.0]hexenes is described. The mild reaction conditions employed allow the efficient and rapid synthesis of a variety of such bicyclic compounds via a sequence of two gold(I)-catalyzed isomerization steps. Acetoxy bicyclo[3.1.0]hexenes products can be further transformed to 2-cycloalkenones by simple methanolysis.     

Copper-catalyzed cycloisomerizations of 5-en-1-yn-3-ols

[reaction: see text] The Cu(I)-catalyzed cycloisomerization of tertiary 5-en-1-yn-3-ols with an 1,2-alkyl shift affords stereoselectively tri- and tetracyclic compounds of high molecular complexity. These results are in agreement with a mechanism in which the cyclopropanation precedes the rearrangement.     

Gold(I)-catalyzed Claisen rearrangement of allenyl vinyl ethers; synthesis of substituted 1,3-dienes

Synthesis of substituted 1,3-dienes was achieved via gold(I)-catalyzed Claisen rearrangement of allenyl vinyl ethers. The N-heterocyclic carbene gold chloride catalyst (IPrAuCl) was superior in terms of activity and selectivity and afforded the 3,3-product in excellent yields. A proposed cation-π inter-action played a significant role in affecting the reaction rate.