Plasmonic heterogeneous catalysis for organic transformations

Plasmonic catalysis has been recognised as a promising alternative to many conventional thermal catalytic processes in organic synthesis. In addition to their high activity in fine chemical synthesis, plasmonic photocatalysts are also able to maintain control of selectivity under mild conditions by utilising visible-light as an energy source. This review provides an overview of the recent advances in organic transformations with plasmonic metal nanostructures, including selective reduction, selective oxidation, cross-coupling and addition reactions. We also summarize the photocatalysts and catalytic mechanisms involving surface plasmon resonance. Finally, control of reaction pathway and strategies for tailoring product selectivity in fine chemical synthesis are discussed.     

Gold catalysis

Catalysis by gold has rapidly become a hot topic in chemistry, with a new discovery being made almost every week. Gold is equally effective as a heterogeneous or a homogeneous catalyst and in this Review we attempt to marry these two facets to demonstrate this new found and general efficacy of gold. The latest discoveries are placed within a historical context, but the main thrust is to highlight the new catalytic possibilities that gold-catalyzed reactions currently offer the synthetic chemist, in particular in redox reactions and nucleophilic additions to pi systems. Indeed gold has proved to be an effective catalyst for many reactions for which a catalyst had not been previously identified, and many new discoveries are still expected.     

金催化剂及其在有机反应中的应用研究进展*

本文综述了金催化剂在选择氧化、选择加氢、不对称醇醛缩合、C-N键生成等多相和均相催化反应中的应用研究,并讨论了各种影响金催化剂催化活性的因素,最后展望了金催化剂的应用前景.     

Gold in total synthesis: alkynes as carbonyl surrogates

Fields of gold: Recent developments in the field of gold catalysis, using an alkyne as a carbonyl equivalent is becoming an important chemical transformation, thus providing flexibility in synthetic planning of complex and sensitive natural products. Understanding of the reaction and new catalyst designs are providing new conditions that are amenable for late-stage synthetic intermediates.     

Acetylene as a Dicarbene Equivalent for Gold(I) Catalysis: Total Synthesis of Waitziacuminone in One Step

The gold(I)‐catalyzed reaction of acetylene gas with alkenes leads to (Z,Z)‐1,4‐disubstituted 1,3‐butadienes and biscyclopropanes depending on the donor ligand on gold(I). Acetylene was generated in situ from calcium carbide and water in a user‐friendly procedure. Reaction of acetylene with 1,5‐dienes gives rise stereoselectively to tricyclo[5.1.0.0^2,4]octanes. This novel double cyclopropanation has been applied to the one step total synthesis of the natural product waitziacuminone from acetylene and geranyl acetone.     

Gold catalysis: no steric limitations in the phenol synthesis

Different dihydroisoindol-4-ols and 8-hydroxytetrahydroisoquinolines were prepared by the gold-catalyzed phenol synthesis. The reaction was investigated with several sterically demanding groups in the 5-position of the furan starting material. The influence of the reaction time and the catalyst on the yield was investigated.     

Clays as selective catalysts in organic synthesis

Suitably modified smectite clays can be very selective catalysts for a wide range of organic reactions. While it has long been known that such materials can act as Bronsted and Lewis acids, it has been shown recently that they are also effective Diels-Alder catalysts. A selection of illustrative reactions is given which emphasises their wide range of use, their selectivity, and the ease of work-up after reaction. In each case, mechanistic information is presented, e.g., on the site of reaction (whether interlayer or surface), rate determining steps, etc. The regiochemical consequences of the restricted reaction space are stressed.Based on material presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Gold catalysis: domino reaction of en-diynes to highly substituted phenols

By Sonogashira coupling of 1,7-heptadiynes and 1,8-octadiynes with 2-iodoallyl alcohols, various substrates that bear a 2-alkynylallyl alcohol moiety tethered to an additional alkyne were prepared in one step. Subjection to nitrogen acyclic carbene (NAC)/gold(I) catalysts delivered highly substituted phenols in an efficient domino reaction. Furan derivatives were formed as intermediates; this was proven by in situ NMR spectroscopy. The uncommon substitution pattern of these furans opens the way for a selective formation of phenols that contain the hydroxyl group in the meta position to the ring junction, which previously was not possible by gold-catalyzed furan-yne cyclization. Furthermore, interesting mechanistic insights were obtained by products derived from secondary allyl alcohols. In this case, in addition to the phenolic compounds, a ketone is formed by 1,2-alkyl shift.     

Gold catalysis: efficient synthesis and structural assignment of jungianol and epi-jungianol

Starting from 2-methylfuran and crotonaldehyde, both jungianol and epi-jungianol were prepared by a six-step sequence including a gold-catalyzed arene synthesis and a photochemical S(N)2-like reduction with lithium aluminum hydride. Not a single protective group was needed in the entire synthesis. With both diastereomers in hand, the stereochemical assignment in the literature could be corrected by means of a thorough (1)H NMR spectroscopic analysis and an X-ray diffraction study on an epi-jungianol derivative.     

Gold catalysis: phenol synthesis in the presence of functional groups

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.     

Two birds with one metallic stone: single-pot catalysis of fundamentally different transformations

Advances in metal catalysis have revolutionized organic synthesis, with the scope of metal-catalyzed reactions now covering nearly all areas of carbon-carbon, carbon-hydrogen, and carbon-heteroatom bond formation. For years, the goal was to develop catalysts that were highly selective for a single transformation. However, a promising current area of research is the use of a single catalyst to mediate more than one transformation in a selective manner. Whereas much early work was focused on using a catalyst for several similar transformations, recent investigations have shown that it is also possible to employ a single catalyst for several very different transformations in a single reaction sequence. This Minireview focuses on methods in which the mechanisms of the transformations are fundamentally very different.