The substrate scope, the mechanistic aspects of the gold-catalyzed oxazole synthesis, and substrates with different aliphatic, aromatic, and functional groups in the side chain were investigated. Even molecules with several propargyl amide groups could easily be converted, delivering di- and trioxazoles with interesting optical properties. Furthermore, the scope of the gold(I)-catalyzed alkylidene synthesis was investigated. Further functionalizations of these isolable intermediates of the oxazole synthesis were developed and chelate ligands can be obtained. The use of Barluenga's reagent offers a new and mild access to the synthetically valuable iodoalkylideneoxazoles from propargylic amides, this reagent being superior to other sources of halogens.

A series of furyl alcohols and homofuryl alcohols was synthesized by reduction of furfurals or reaction of furyllithium compounds with epoxides and subsequent propargylation. The gold-catalyzed cycloisomerization of these products furnished dihydroisobenzofurans and isochromanes. Crystal structure analyses proved the sequence of the substituents for both classes of products. Unsaturated dicarbonyl compounds as side-products show the mechanistic relationship to the analogous platinum-catalyzed reactions. Neither ester groups, even on the 4-position of the furan ring, nor aryl bromides hinder the catalysis by gold. In the case of a substrate with an allyl ether in the side chain, a side-product, which provides evidence for a reaction of the alkyne with an inverse regioselectivity, was observed.

Changing tracks: By the use of alkynyl ethers as directing elements, the furan‐yne cyclization enters a new reaction pathway. Instead of phenols, tetracycles containing two heteroatoms and two new stereocenters are formed (see scheme).

A gold-catalyzed phenol synthesis was successfully used in the synthesis of dihydroisocoumarins for the first time. A large number of gold(i) complexes were prepared and tested; only complexes based on the biarylphosphine motif were successful.

Homogeneous gold catalysis has made a major contribution to organic synthesis in the past decade [1] and, apart from significant methodology work in the meantime, it has become an efficient tool in total synthesis.[2] It has almost been forgotten that enantioselective gold catalysis was the origin of homogenous gold catalysis.[3] After significant initial success, [4] stereoselective gold catalysis was neglected for some time. As recently predicted, [5] enantioselective gold catalysis revived in the last years and significant success has been achieved with a number of different enantiomerically pure gold complexes [6] and even enantiomerically pure counterions. [7] Common for these enantioselective reactions is that the new stereocenters are formed by the transformation of a sp 2 center of a C=C double bond (in an allene or alkene 1, Scheme 1) to a chiral center with sp 3 hybridization in the product 2. Alternatively, a C=O double bond (in an aldehyde) is transformed. So far only an enantiofacial selection in the selectivity determining step has been exploited for enantioselective homogeneous gold catalysis.With mono-alkynes, such a facial selection is not possible-the typical addition reactions initially form alkenes that do not possess a stereocenter. Dialkynes 3 with symmetry equivalent, enantiotopic alkynyl groups would allow stereoselective conversions. If, after the coordination (an intermolecular process) of the alkyne to the enantiomerically pure gold catalyst, the subsequent intramolecular addition is fast for both diastereomeric p complexes (leading to the two enantiomeric products 4 and ent-4; in general, gold-catalyzed reactions are fast compared to other catalysts). The stereoselection would be quite difficult, as the p coordination of one of the two alkynes to the gold catalyst would become the selectivity determining step (in general, the subsequent addition reactions are not reversible).Here we report our findings with regard to this concept in the gold-catalyzed phenol synthesis. [8] As the test substrate for this investigation, we used the furyldialkyne 8. It was easily prepared from 5-methylfurfural (5) by an aldol condensation with tert-butyl acetate to deliver the furylacrylate 6, followed by chemoselective transfer hydrogenation to give 7 and twofold addition of propargyl magnesium bromide to the ester group (Scheme 2).With 5 mol % AuCl 3 this substrate 8 readily and chemoselectively underwent cycloisomerization to the phenol rac-9