Dedicated to Professor Johann Mulzer on the occasion of his 60th birthdayThe catalysis of organic reactions by gold compounds has been recently shown to be a powerful tool in synthesis. [1, 2] When gold(i) compounds are used as precatalysts, ligands such as phosphanes [3][4][5][6][7][8] or phosphites [9] can be applied. The gold(iii) precatalysts are mainly simple halides; [2] other examples include one thioether-containing, [10] one phosphite-containing, [9] and organogold(iii) [11] compounds. For the gold-catalyzed phenol synthesis, [12] AuCl 3 usually delivers good results with simple substrates, but with more complicated ones a significant loss of activity is observed. At lower temperature, kinetic studies with our most simple testsubstrate 1 (see Scheme 1) showed that the problem with regard to the loss of activity occurs even with as much as 5 mol % of catalyst ( Figure 1). With small amounts of catalyst, the conversion remains incomplete.We have now tested several gold(i) and gold(iii) complexes with different ligands as catalysts for this reaction. Gold(i) complexes showed low selectivity and led to several side products. Satisfactory results in terms of activity, long-term stability and product-selectivity were obtained only with gold(iii) complexes with pyridine derivatives, some of which contained chelating oxygen functionalities. The most interesting complexes were precatalysts 3-6.[13] The complexes did not suffer deactivation, as shown in Figure 2 for 3-the activity even holds in a second catalytic run. Unlike with AuCl 3 , a mechanistically interesting induction period was observed for 3-6, clearly proving that here the complexes are precatalysts. This is also the reason for the higher activity in the second run, since the catalytically active species is already present and does not have to be formed in a slow reaction.With as little as 0.07 mol % of 3 a complete conversion could be achieved; this corresponds to 1180 instead of the usual 20-50 turnovers. The complexes 4-6 are also highly stable catalysts; a comparison of their activity is depicted in Figure 3: the acceptor-substituted pyridine carboxylate 5 is the most reactive one, followed by the unsubstituted 4 and the donor-substituted 6. Nevertheless, the initial activity of 3, 4, and 6 is lower than that of AuCl 3 . In part, this problem can be solved by switching to dichloromethane/acetonitrile mixtures or even pure dichloromethane (as shown for 3 in Figure 4). In

Reaction of the cationic binuclear gold(I) complex [(Ph 3 PAu) 2 Cl]BF 4 with w-alkynylfurans furnished phenols as the major product and anellated furans as the side-products. The analogous trimesitylphosphane complex [(Mes 3 PAu) 2 Cl]BF 4 selectively afforded only the phenols. The latter catalyst then enabled the first intermolecular gold-catalyzed phenol synthesis.

A ketal group in a furyl position affords arene oxides from g-alkynylfurans even with the simple goldA C H T U N G T R E N N U N G (III) chloride (AuCl 3 ) catalyst. These can either undergo Diels-Alder reactions, isomerise to stable oxepines by an oxygen-walk reaction or by the addition of water selectively be converted to phenols which differ in the position of the hydroxy group from the normal phenols formed in the gold-catalysed phenol synthesis. With a phenyl substituent on the furan, the 2-hydroxymethylpyridinato-goldA C H T U N G T R E N N U N G (III) complex, not the usual arene oxide but an oxepine is obtained, still the arene oxide can be trapped from the valence-tautomeric equilibrium by a Diels-Alder reaction.

The effect of different substituents, such as bromo, chloromethyl, hydroxymethyl, formyl, acetyl, carboxy, and acylated hydroxymethyl and ammonium groups, on the furan ring of substrates in gold-catalyzed phenol synthesis has been investigated. The furan ring was also replaced by different heterocycles, such as pyrroles, thiophenes, oxazoles, and a 2,4-dimethoxyphenyl group; gold catalysis then delivered no phenols, but occasionally other products were obtained. [Ru(3)(CO)(12)] also catalyzed the conversion of 1 at a low rate, [Os(3)(CO)(12)] failed as a catalyst, and with [Co(2)(CO)(8)] the alkyne complex 19 can be obtained, it does not lead to any phenol but reacts with norbornene to give the product of a Pauson-Khand reaction. Efforts to prepare vinylidene complexes of 1 provided the only evidence for these species; in the presence of a phosphane ligand with ruthenium an interesting deoxygenation to 22 was observed. The phenol 2 c was converted to the allyl ether, a building block for para-Claisen rearrangements, and to the aryl triflate, a building block for cross-coupling reactions.

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A new route to enantiomerically pure 8-hydroxytetrahydroisoquinolines is based on furan derivatives and amino acids from renewable resources and gold catalysis. The stereogenic centre from the amino acid remains unchanged in the product.

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Indole derivatives R 0140Gold Catalysis: Phenol Synthesis in the Presence of Functional Groups. -The effect of different substituents at the furan ring in the substrates is investigated. It is shown that substituents which deactivate the π system of the furan are not tolerated. If the furan ring is replaced by other heterocycles, gold catalysis affords no phenols. -(HASHMI*, A. S. K.; WEYRAUCH, J. P.; KURPEJOVIC, E.; FROST, T. M.; MIEHLICH, B.; FREY, W.; BATS, J. W.; Chem. Eur. J. 12 (2006) 22, 5806-5814; Inst. Org. Chem., Univ. Stuttgart, D-70569 Stuttgart, Germany; Eng.) -Bartels 47-126