Asymmetric total synthesis of (-)-indicol by a carbene cyclization-cycloaddition cascade strategy

The first total synthesis of a secodolastane, (-)-indicol, has been accomplished. The key reaction is a rhodium(II)-mediated carbene cyclization-cycloaddition cascade, by which the core bicyclo[5.4.0]undecane skeleton was assembled. In this one-pot reaction, a domino series of transformations resulting in the construction of three sigma bonds and three stereocenters was realized in good yield.     

A formal total synthesis of (±)-9-isocyanoneopupukeanane

A formal total synthesis of the marine sesquiterpene (±)-9-isocyanoneopupukeanane starting from the readily available monoterpene carvone has been accomplished employing a combination of intermolecular Michael addition-intramolecular Michael addition reaction and an intramolecular rhodium carbenoid C-H insertion reaction as key steps, and identifying the isopropenyl group as a masked hydroxy group.     

An expedient enantioselective route to diaminotetralins: application in the preparation of analgesic compounds

Advances to the rhodium-catalyzed asymmetric ring-opening protocol have allowed this methodology to be extended to azabicyclic alkenes, the first time that rhodium has been used in allylic functionalizations with nitrogen leaving groups. The product diaminotetralins are important medicinal compounds. The synthetic utility of this methodology has been demonstrated in the total synthesis of an analgesic compound where the tetralin core, the regiochemistry, and the relative and absolute stereochemistry are all established in the ring-opening step. [reaction: see text]     

Asymmetric Total Synthesis of (−)‐Maoecrystal V

The asymmetric total synthesis of (?)‐maoecrystal V, a novel cytotoxic pentacyclic ent‐kaurane diterpene, has been accomplished. Key steps of the current strategy involve an early‐stage semipinacol rearrangement reaction for the construction of the C10 quaternary stereocenter, a rhodium‐catalyzed intramolecular O?H insertion reaction, and a sequential Wessely oxidative dearomatization/intramolecular Diels–Alder reaction to forge the pentacyclic framework of maoecrystal V.     

Further observations on the rhodium (I)-catalysed tandem hydrosilylation-intramolecular aldol reaction

The rhodium (I) catalysed tandem hydrosilylation-intramolecular aldol reaction provides a simple strategy for construction of a range of usefully functionalised five-membered rings from readily prepared 6-oxo-2-hexenoates in good yield and with good to excellent stereoselectivity. A series of silanes and rhodium catalysts have been investigated. Stereoselectivity proved to be highly dependant on the catalyst as well as on the substitution pattern of the parent substrate. The extension of this methodology for the synthesis of larger ring sizes has also been evaluated.     

Rhodium Enalcarbenoids: Direct Synthesis of Indoles by Rhodium(II)‐Catalyzed [4+2] Benzannulation of Pyrroles

Disclosed herein is the design of an unprecedented electrophilic rhodium enalcarbenoid which results from rhodium(II)‐catalyzed decomposition of a new class of enaldiazo compounds. The synthetic utility of these enalcarbenoids has been successfully demonstrated in the first transition‐metal‐catalyzed [4+2] benzannulation of pyrroles, thus leading to substituted indoles. The new benzannulation has been applied to the efficient synthesis of the natural product leiocarpone as well as a potent adipocyte fatty‐acid binding protein inhibitor.     

Total Synthesis of the Post‐translationally Modified Polyazole Peptide Antibiotic Goadsporin

The structurally unique polyazole antibiotic goadsporin contains six heteroaromatic oxazole and thiazole rings integrated into a linear array of amino acids that also contains two dehydroalanine residues. An efficient total synthesis of goadsporin is reported in which the key steps are the use of rhodium(II)‐catalyzed reactions of diazocarbonyl compounds to generate the four oxazole rings, which demonstrates the power of rhodium carbene chemistry in organic chemical synthesis.     

The interaction of rhodium carbenoids with carbonyl compounds as a method for the synthesis of tetrahydrofurans

The transition metal catalyzed reaction of α-diazo carbonyl compounds has found numerous applications in organic synthesis, and its use in either heterocyclic or carbocyclic ring formation is well precedented. In contrast to other catalysts that are suitable for carbenoid reactions of diazo compounds, those constructed with the dirhodium(II) framework are most amenable to ligand modification that, in turn, can influence reaction selectivity. The reaction of rhodium carbenoids with carbonyl groups represents a very efficient method for generating carbonyl ylide dipoles. Rhodium-mediated carbenoid–carbonyl cyclization reactions have been extensively utilized as a powerful method for the construction of a variety of novel polycyclic ring systems. This article will emphasize some of the more recent synthetic applications of the tandem rhodium carbenoid cyclization/cycloaddition cascade for natural product synthesis. Discussion centers on the chemical behavior of the rhodium metal carbenoid complex that is often affected by the nature of the ligand groups attached to the metal center.     

Rhodium(III)‐Catalyzed Transannulation of Cyclopropenes with N‐Phenoxyacetamides through CH Activation

An efficient rhodium(III)‐catalyzed synthesis of 2H‐chromene from N‐phenoxyacetamides and cyclopropenes has been developed. The reaction represents the first example of using cyclopropenes as a three‐carbon unit in rhodium(III)‐catalyzed C(sp²)? H activations.     

Rhodium(III)-catalyzed C-H alkylation of heterocycles with allylic alcohols in water: A reusable catalytic system for the synthesis of β-aryl ketones

A highly efficient, green and sustainable protocol for rhodium(III)-catalyzed C-H alkylation of heterocycles with allylic alcohols has been achieved, which affords a series of β-aryl ketones in high yields. The reaction proceeds smoothly in water under air, and works well with heterocycles such as indoles, indolines, pyrroles and carbazoles. Notably, the expensive rhodium catalyst in water could be easily separated from the organic products, and reused for at least five times without loss of its catalytic activity and selectivity, which is a promising, green and sustainable pathway for the synthesis of β-aryl ketones. To the best of our knowledge, this is the first example for the reuse of expensive rhodium catalyst in water.     

Rhodium(III)‐Catalyzed Transannulation of Cyclopropenes with N‐Phenoxyacetamides through C?H Activation

An efficient rhodium(III)‐catalyzed synthesis of 2H‐chromene from N‐phenoxyacetamides and cyclopropenes has been developed. The reaction represents the first example of using cyclopropenes as a three‐carbon unit in rhodium(III)‐catalyzed C(sp²) H activations.     

Enantioselective Hydrogenation of Acetophenone over Cinchonidine-Stabilized and Supported Rhodium Clusters

Because of the importance of the chirality in chemicals in everyday, the synthesis of enantiomerically pure chiral compounds has become an important academic and commercial advantage. In asymmetric synthesis field, enantioselective catalysis has been the most challenging subject over the past decades. Among the numerous enantioselective heterogeneous catalysts, the rhodium is always an unsuccessful example under favorable reaction conditions with only 20%-30% enantiomeric excess (e.e.)^[1].And almost all of papers about heterogeneous enantioselective catalysis have reported that rhodium is not suitable for heterogeneous enantioselective hydrogenation^[1-3].     

Hydroformylation activity of multinuclear rhodium complexes coordinated to dendritic iminopyridyl and iminophosphine scaffolds

The synthesis of poly(propyleneimine)-iminopyridyl and iminophosphine rhodium(I) metallodendrimers, with rhodium coordinated to monodentate (N-donor) and chelating, heterobidentate (P,N) moieties respectively located on the periphery, has been accomplished in order to evaluate their potential as hydroformylation catalysts. Related mononuclear complexes were obtained in a similar manner to model the multinuclear complexes. The multinuclear rhodium(I) complexes were found to be effective catalyst precursors in the hydroformylation of 1-octene, achieving higher conversions, faster reaction rates and slightly enhanced catalytic activity when compared with analogous mononuclear rhodium complexes. Hydroformylation reactions using the tetra- and octanuclear rhodium complexes generally show a chemoselective formation of aldehydes, together with a small amount of isomerisation products.     

Asymmetric Synthesis of Protected Cyclohexenylamines and Cyclohexenols by Rhodium‐Catalyzed [2+2+2] Cycloaddition

It has been established that cationic rhodium(I)/axially chiral biaryl bis(phosphine) complexes catalyze the asymmetric [2+2+2] cycloaddition of 1,6‐enynes with electron‐rich functionalized alkenes, enamides, and vinyl carboxylates, to produce the corresponding protected cyclohexenylamines and cyclohexenols. Interestingly, regioselectivity depends on structures of substrates. The present cycloaddition was successfully applied to the enantioselective total synthesis of (?)‐porosadienone by using the amide moiety as a leaving group.     

Total Synthesis of (+)‐Asteriscanolide: Further Exploration of the Rhodium(I)‐Catalyzed [(5+2)+1] Reaction of Ene‐Vinylcyclopropanes and CO

The total synthesis of (+)‐asteriscanolide is reported. The synthetic route features two key reactions: 1) the rhodium(I)‐catalyzed [(5+2)+1] cycloaddition of a chiral ene‐vinylcyclopropane (ene‐VCP) substrate to construct the [6.3.0] carbocyclic core with excellent asymmetric induction, and 2) an alkoxycarbonyl‐radical cyclization that builds the bridging butyrolactone ring with high efficiency. Other features of this synthetic route include the catalytic asymmetric alkynylation of an aldehyde to synthesize the chiral ene‐VCP substrate, a highly regioselective conversion of the [(5+2)+1] cycloadduct into its enol triflate, and the inversion of the inside–outside tricycle to the outside–outside structure by an ester‐reduction/elimination to enol‐ether/hydrogenation procedure. In addition, density functional theory (DFT) rationalization of the chiral induction of the [(5+2)+1] reaction and the diastereoselectivity of the radical annulation has been presented. Equally important is that we have also developed other routes to synthesize asteriscanolide using the rhodium(I)‐catalyzed [(5+2)+1] cycloaddition as the key step. Even though these routes failed to achieve the total synthesis, these experiments gave further useful information about the scope of the [(5+2)+1] reaction and paved the way for its future application in synthesis.     

Review of Acetic Acid Synthesis from Various Feedstocks Through Different Catalytic Processes

Acetic acid (AA) has been largely used with a wide range of applications such as a raw material for a synthesis of vinyl acetate monomer, cellulose acetate or acetate anhydrate, acetate ester and a solvent for a synthesis of terephthalic acid and so on. The present paper briefly summarizes the commercialized chemical processes with their Rh or Ir-based catalytic systems in a liquid-phase carbonylation reaction such as Monsanto, Cativa and Acetica processes. In addition, some alternative catalytic systems such as heterogeneous catalysts to produce AA by direct oxidation or indirect carbonylation of dimethyl ether through BP-SaaBre process in a gas-phase reaction to solve some problems such as a difficult separation of homogeneous catalysts in a corrosive reaction medium. Some home-made heterogeneous catalysts such as a rhodium incorporated graphitic carbon nitride (Rh-g-C₃N₄) and some heterogenized homogeneous catalysts using the supports of tungsten carbide, iron oxide or graphitic carbon nitride containing rhodium complexes were also introduced for the synthesis of AA through a liquid-phase methanol carbonylation reaction to effectively solve the leaching problem of active rhodium metal as well as to mitigate the separation problem of homogeneous catalysts.     

Abnormal oxazol-4-ylidene and thiazol-4-ylidene rhodium complexes: synthesis, structure, and properties

A series of new 2,3,5-triaryl-substituted oxazolium and thiazolium salts are readily prepared by a Tf(2)O-mediated intramolecular cyclisation and their use as precursors for the synthesis of novel oxazol-4-ylidene and thiazol-4-ylidene rhodium complexes has been developed.     

Synthesis and reactions of rhodium compounds containing tellurium donor ligands

This paper describes the synthesis and characterization of a series of rhodium(I) and rhodium(III) complexes containing tellurium-rhodium bonds resulting from the coordination of diorgano telluride or organotelluro ligands. Oxidative addition, metathesis and substitution reactions of these compounds have been examined, and the resulting products are compared with those from the known reactions of rhodium(I) and rhodium(III) compounds containing phosphine ligands.     

Novel rhodium-catalyzed cycloisomerization of 1,6-enynes with an intramolecular halogen shift

A new Rh-catalyzed 1,6-enyne cycloisomerization process with a pi-allyl rhodium species as the key intermediate is investigated. A halogen shift happened in this novel process. The synthesis of stereodefined alpha-halomethylene gamma-butyrolactones has been achieved using the readily accessible Rh catalysts.     

Enantiospecific first total synthesis of (6S,7R)-silphiperfolan-6-ol

Enantiospecific first total synthesis of the angular triquinane sesquiterpene (6S,7R)-silphiperfolan-6-ol has been accomplished, starting from 2-(3-isopropenyl-2-methylene-1-methylcyclopent-1-yl)acetic acid (readily available from (R)-limonene) employing an efficient, regioselective intramolecular rhodium carbenoid insertion into the CH bond of a tertiary methyl group as the key step.