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Diyne substrates bearing one propargylic ether instead of the previously published propargylic acetates were subjected to a gold catalyst. α−Naphthol derivatives were obtained as products of the cycloisomerization. The close relationship of the products to the corresponding cyclizations implicated a related mechanistic scenary at first, but further studies favour a mechanistic pathway that is completely different.

Aromatic diyne systems bearing one terminal propargylic acetate moiety and one tertiary propargylic alcohol subunit were converted in the presence of a gold catalyst. After an initial 1,2-migration of the acetoxy group at the terminal alkyne, a gold carbenoid is formed which is then transferred onto the internal alkyne of the propargylic alcohol. This combination enables the use of propargylic acetates as precursors for a gold-catalyzed pinacol-type rearrangement. In the final pinacol-like step the shift of an alkyl or aryl moiety onto an electrophilic gold carbenoid/cation terminates the reaction and 1-naphthyl ketones are obtained as products. If electron-rich aromatic backbones are used, a mechanistically interesting alternative pathway including a retro-Buchner reaction is opened.

Gold carbenes generated via 1,2-migration of a propargylic ester group can be transferred over a tethered alkyne. The use of aromatic backbones leads after a 1,7-carbene transfer to a benzyl-stabilized carbene as intermediate. A 1,2-shift of a methyl group delivers vinyl-substituted β-naphthol derivatives as the final products.

1,6-Diyne-4-en-3-ols with one terminal alkyne were applied as test substrates for a possible dual catalyzed cyclization. Instead of a dual catalysis cycle, naphthyl ketone derivatives were obtained as single products. The regioselectivity of the obtained products is unprecedented. Instead of the expected naphthyl ketones bearing the keto group in the α-position, the keto group is positioned in the s-position of the naphthyl skeleton by a complex rearrangement of the starting materials.

A protocol for the gold-catalyzed cycloisomerization of propargyl ethers bearing a second triple bond is presented.

Aromatic diyne systems bearing one terminal propargylic acetate moiety and one tertiary propargylic alcohol subunit were converted in the presence of a gold catalyst. After an initial 1,2-migration of the acetoxy group at the terminal alkyne, a gold carbenoid is formed which is then transferred onto the internal alkyne of the propargylic alcohol. This combination enables the use of propargylic acetates as precursors for a gold-catalyzed pinacol-type rearrangement. In the final pinacol-like step the shift of an alkyl or aryl moiety onto an electrophilic gold carbenoid/cation terminates the reaction and 1-naphthyl ketones are obtained as products. If electron-rich aromatic backbones are used, a mechanistically interesting alternative pathway including a retro-Buchner reaction is opened.

(S)-6-(4-(Methoxycarbonyl)phenyl)-1,1'-bis-2-naphthol, a chiral 1,1'-bis-2-naphthol (BINOL) derivative, was prepared via Suzuki C¢C coupling and immobilized onto diamine- functionalized multiwalled carbon nanotubes. The BINOL was first derivatized with a carboxylic acid, capable of forming an amide linkage with the amine-carbon nanotube modified surface. The 4-methoxyphenylboronic acid was replaced by 3-fluoro-4-(methoxycarbonyl)phenylboronic acid and (S)-6-(3-fluoro-4-(methoxycarbonyl)phenyl)-1,1'-bis-2- naphthol was obtained and used as a probe to better quantify the organic material. It was found that in the hybrid material, 1/3 of amine groups have been transformed into the corresponding amide (S)-BINOL derivative. The chemical and electronic integrity of the chiral BINOL ligand is maintained after the ligand immobilization. Evaluation in diethyl zinc and Ti(OiPr)4-catalyzed alkylation of benzaldehyde showed that both methoxycarbonylphenyl and fluoromethoxycarbonylphenyl BINOL moieties do not significantly influence the catalytic activity or selectivity of the process. However, when hybrid materials were used, similar activities were obtained, but with lower enantioselectivities. This result could be due to a competitive alkylation reaction occurring on the carbon surface or by the constraint caused by the ligand proximity on the support surface.

Transformation of norbornene under the investigated conditions suffers from incomplete conversion, but succeeds with gold (I) chloride as the catalyst.

Treatment of bisalkynyl substrates (I) and (III) with catalytic amounts of AuCl results in the formation of vinyl-substituted β-naphthol derivatives.

In the presence of a gold catalyst an unprecedented oxidative cyclization of diynes takes place.

This review summarizes the isolated organometallic compounds which represent analogues of intermediates of homogeneous gold-catalyzed organic reactions or authentic intermediates isolated under specific reaction conditions preventing a full turnover of the catalytic cycle. This covers π-complexes of gold with coordinated alkenes, arenes, allenes, and alkynes. But also subsequent intermediates of typical catalytic cycles like vinylgold complexes, alkylgold complexes, and gold hydrides. The geminal diaurated complexes, which in the context of dual gold catalysis became an important topic again, and gold carbenoids represent another subject. Both the oxidation states gold(I) and gold(III) are included.

The catalytic cycle involves the formation of gold acetylides and vinylgold intermediates which undergo an unprecedented iodine/gold exchange.

The gold-catalyzed cyclization of 1,6-diynes does not give the expected α-ketonaphthalenes.

In the presence of a gold catalyst an unprecedented oxidative cyclization of diynes takes place. The reaction cascade is initiated by an oxygen transfer from a N-oxide onto a gold-activated alkyne. The formed α-oxo carbene is transferred across the second alkyne yielding a stabilized vinyl carbene/cation. Alkyl migration or sp(3)-CH insertion then terminates the catalytic cycle by formation of highly substituted functionalized indenones. A 1,6-carbene shift could be supported by the oxidation of the vinyl carbene. This protocol represents an attractive alternative to procedures which are based on the metal-catalyzed decomposition of hazardous, not easily accessible, diazo compounds.

We report the gold-catalyzed synthesis of highly functionalized iodofulvenes from iododialkynes under mild conditions. The catalytic cycle involves the formation of gold acetylides and vinylgold intermediates. These intermediates can then undergo an unprecedented iodine/gold exchange. This new pathway for catalyst transfer in dual gold catalysis opens up the possibility of highly regioselective transformations directed by the gold in the organogold intermediates. The resulting products are well suited for further metal-mediated coupling reactions, allowing the synthesis of extended π-systems.

Submitted by Fátima Piedade (fpiedade@sa.isel.pt) on 2013-11-08T11:12:38Z No. of bitstreams: 1 Homogeneous and heterogenised new gold C-scorpionate complexes as catalysts for cyclohexane oxidation.rep.pdf: 206898 bytes, checksum: ccfbb5f52dc9dfb4204db6770f37424a (MD5) Made available in DSpace on 2013-11-08T11:12:38Z (GMT). No. of bitstreams: 1 Homogeneous and heterogenised new gold C-scorpionate complexes as catalysts for cyclohexane oxidation.rep.pdf: 206898 bytes, checksum: ccfbb5f52dc9dfb4204db6770f37424a (MD5) Previous issue date: 2013

A series of dinuclear gold σ,π-propyne acetylide complexes were prepared and tested for their catalytic ability in dual gold catalysis that was based on the reaction of an electrophilic π-complex of gold with a gold acetylide. The air-stable and storable catalysts can be isolated as silver-free catalysts in their activated form. These dual catalysts allow a fast initiation phase for the dual catalytic cycles without the need for additional additives for acetylide formation. Because propyne serves as a throw-away ligand, no traces of the precatalyst are generated. Based on the fast initiation process, side products are minimized and reaction rates are higher for these catalysts. A series of test reactions were used to demonstrate the general applicability of these catalysts. Lower catalyst loadings, faster reaction rates, and better selectivity, combined with the practicability of these catalysts, make them ideal catalysts for dual gold catalysis.