A simple asymmetric organocatalytic approach to optically active cyclohexenones

Asymmetric Synthesis of α-Arylcyclohexenones Catalyzed by Diphenylprolinol Silyl Ether

A general methodology for the asymmetric synthesis of α-arylcyclohexeneones from arylacetones and α,β-unsaturated aldehydes catalyzed by diphenylprolinol silyl ether followed by p-TSA-mediated cyclization is developed. A variety of arylacetones and α,β-unsaturated aldehydes were successfully converted to α-arylcyclohexeneones in 34-67% yield, 10:1-100:0 dr, and 81-99% ee. The scalability of this methodology by a gram-scale synthesis and their utility by converting the product to the corresponding epoxide, alcohol, and diol are demonstrated.

Enantioselective and collective total synthesis of pentacyclic 19-nor-clerodanes

We report herein the collective asymmetric total synthesis of seven pentacyclic 19-nor-clerodane diterpenoids, namely (+)-teucvin (+)-cracroson A, (+)-cracroson E, (+)-montanin A, (+)-teucvisin C, (+)-teucrin A, and (+)-2-hydroxyteuscorolide. An ytterbium-catalyzed asymmetric inverse-electron-demand Diels-Alder reaction of 4-methyl-2-pyrone with a chiral C5-substituted cyclohexa-1,3-dienol silyl ether is the key feature of the synthesis, which provides the common cis-decalin intermediate with five continuous stereocenters in excellent yield and stereoselectivity. From this diversifiable intermediate, the total synthesis of (+)-teucvin and (+)-2-hydroxyteuscorolide was realized in thirteen and eighteen steps, respectively. From (+)-teucvin, five other pentacyclic 19-nor-clerodanes were divergently and concisely generated through late-stage oxidation state adjustments.

Asymmetric Total Synthesis of Brasiliquinones B and C via Oxidative Cyclization of a Hydroquinone-Silyl Enol Ether Hybrid

The asymmetric total synthesis of angucycline antibiotics (S)-brasiliquinones B and C was accomplished. The benz[a]anthraquinone core was constructed via oxidative cyclization of a hydroquinone-silyl enol ether hybrid. The resultant pentacyclic acetal was converted to the silyl enol ether, which was treated with Pd(II)/O₂ to afford brasiliquinone C, after multistep conversion including dehydrogenation, desilylation and deacetalization, and hydroquinone oxidation. The (S)-configuration of natural brasiliquinones was confirmed based on the stereochemical correlation with the synthetic products.

Enantioselective Organocatalytic Conjugate Addition in a Tandem Synthesis of δ-Substituted Cyclohexenones and Four-Step Total Synthesis of Penienone

A bisperfluorotoluyl-BINOL catalyzed conjugate addition of trifluoroborate salts to doubly vinylogous esters and aldol condensation synthesized chiral δ-substituted cyclohexenones with high yields and enantioselectivities (10 examples, up to 89% yield, 89-98% ee). Stepwise and single-pot sequences were developed, with the former also providing β-substituted masked ketoaldehydes containing a vinyl ether. The transformation was used in a four-step total synthesis of penienone (24% overall yield), ≤ half the steps as in previous syntheses.

Asymmetric Michael reaction of malononitrile and α,β-unsaturated aldehydes catalyzed by diarylprolinol silyl ether

The asymmetric Michael reaction of malononitrile and α,β-unsaturated aldehydes catalyzed by diarylprolinol silyl ether was developed. Michael products were obtained in good yield and with excellent enantioselectivity without formation of overreaction products. As a malononitrile moiety can be transformed into alkoxy or amino carbonyl moieties by oxidative transformation, an α-chiral ester or amide with an all-carbon quaternary center can be synthesized with excellent enantioselectivity.

How to Make a Cocktail of Palladium Catalysts with Cola and Alcohol: Heteroatom Doping vs. Nanoscale Morphology of Carbon Supports

Sparkling drinks such as cola can be considered an affordable and inexpensive starting material consisting of carbohydrates and sulfur- and nitrogen-containing organic substances in phosphoric acid, which makes them an excellent precursor for the production of heteroatom-doped carbon materials. In this study, heteroatom-doped carbon materials were successfully prepared in a quick and simple manner using direct carbonization of regular cola and diet cola. The low content of carbon in diet cola allowed reaching a higher level of phosphorus in the prepared carbon material, as well as obtaining additional doping with nitrogen and sulfur due to the presence of sweeteners and caffeine. Effects of carbon support doping with phosphorus, nitrogen and sulfur, as well as of changes in textural properties by ball milling, on the catalytic activity of palladium catalysts were investigated in the Suzuki–Miyaura and Mizoroki–Heck reactions. Contributions of the heteroatom doping and specific surface area of the carbon supports to the increased activity of supported catalysts were discussed. Additionally, the possibility of these reactions to proceed in 40% potable ethanol was studied. Moreover, transformation of various palladium particles (complexes and nanoparticles) in the reaction medium was detected by mass spectrometry and transmission electron microscopy, which evidenced the formation of a cocktail of catalysts in a commercial 40% ethanol/water solution.

Synthesis of Highly Functionalized Hydrindanes via Sequential Organocatalytic Michael/Mukaiyama Aldol Addition and Telescoped Hydrozirconation/Cross-Coupling as Key Steps: En Route to the AB System of Clifednamides

The AB ring systems of the clifednamide family, polycyclic tetramate macrolactames (PoTeMs), were prepared by a new, convergent approach employing an intramolecular Diels-Alder (IMDA) reaction. Key steps comprise an organocatalytic Michael addition (>90% enantiomeric excess (ee)), a Mukaiyama aldol reaction for the convergent installation of a diene moiety, and a telescoped hydrozirconation/cross-coupling grafting an enone. The following IMDA furnished a highly functionalized hydrindane (diastereomeric ratio (dr) = 91:1) with the same configuration as the clifednamide scaffold. Advantages of this route are only one required protecting group, 13% overall yield over 9 steps (reduced from previously 17 steps/1.3% overall), and the potential access to the key intermediates in the clifednamide biosynthesis.

Copper Catalyzed Decarboxylative Functionalization of Ketoacids

Selective copper catalyzed activation of ketoacids and notably bio-sourced 1,3-acetonedicarboxylic acid, represents an attractive strategy to solve key synthetic challenges. Condensation with aldehydes under exceedingly mild conditions can create more rapidly known natural products scaffolds such as 1,3 polyols. In this account, the recent progress in this field, notably through multicatalytic combination with organocatalysis is described. In addition to the rapid preparation of natural product fragments, cascade incorporation of fluorine also provided new type of synthetic analogues of improved properties in a broad range of applications.

Sprouting "sustainability" in chemical sciences curriculum

The purpose of this paper is to present a new viewpoint on how the curricula for higher education chemistry courses can be restructured, so that students understand the various dimensions of the sustainability concept and are equipped to work chemical sciences in a profitable, clean and societal friendly way, that is synthesis of materials (which collates CHNOPS-atomic symbols) in desired architecture and disperse them after their intended use, back into their natural reservoirs. A very novel idea of "sustainable chemical science facility", encompassing a teaching module capable of imparting strong fundamental Chemistry concepts, a virtual environment for undergoing the basic industrial training and a production unit with modular reactors for resource funding is proposed here. Often research is restricted to academic qualification, and a substantial band gap exists between the microscopic realm of academic research and the macroscopic domain of industrial chemistry, which thrives on research application. This band gap can be overcome by arming young chemists with training, tools and experience to possess complete control (synthetic and functional) on the materials they produce. The conceptual facility if turned into reality will definitely be the right step towards achieving materials with sustainable functionalities. We will have learning, training and production under one roof. Students will receive theoretical, practical and real-life experience of the production in industries, making them efficiently employable at a very young age. The idea is to bridge some critical engineering concepts with core chemistry, but with a clear distinction between chemical reactor engineering and core chemistry. This paper is a brainchild of the author and is more of a policy paper, needed to be elaborately discussed in academic and industrial forums.

Advances in the Asymmetric Total Synthesis of Natural Products Using Chiral Secondary Amine Catalyzed Reactions of α,β-Unsaturated Aldehydes

Chirality is one of the most important attributes for its presence in a vast majority of bioactive natural products and pharmaceuticals. Asymmetric organocatalysis methods have emerged as a powerful methodology for the construction of highly enantioenriched structural skeletons of the target molecules. Due to their extensive application of organocatalysis in the total synthesis of bioactive molecules and some of them have been used in the industrial synthesis of drugs have attracted increasing interests from chemists. Among the chiral organocatalysts, chiral secondary amines (MacMillan's catalyst and Jorgensen's catalyst) have been especially considered attractive strategies because of their impressive efficiency. Herein, we outline advances in the asymmetric total synthesis of natural products and relevant drugs by using the strategy of chiral secondary amine catalyzed reactions of α,β-unsaturated aldehydes in the last eighteen years.

l-Phenylalanine potassium catalyzed asymmetric formal [3 + 3] annulation of 2-enoyl-pyridine N-oxides with acetone

A highly enantioselective formal [3 + 3] annulation of 2-enoyl-pyridine N-oxides with acetone was developed.

Organocatalytic asymmetric synthesis of cornolactones A and B, and formal synthesis of brasoside and littoralisone

The asymmetric total or formal syntheses of cornolactone A, cornolactone B, brasoside and littoralisone were accomplished in short steps.

Enantioselective Organocatalyzed Transformations of β-Ketoesters

The β-ketoester structural motif continues to intrigue chemists with its electrophilic and nucleophilic sites. Proven to be a valuable tool within organic synthesis, natural product, and medicinal chemistry, reports on chiral β-ketoester molecular skeletons display a steady increase. With the reignition of organocatalysis in the past decade, asymmetric methods available for the synthesis of this structural unit has significantly expanded, making it one of the most exploited substrates for organocatalytic transformations. This review provides comprehensive information on the plethora of organocatalysts used in stereoselective organocatalyzed construction of β-ketoester-containing compounds.

An Asymmetric Organocatalytic Quadruple Domino Reaction Employing a Vinylogous Friedel-Crafts/Michael/Michael/Aldol Condensation Sequence

An organocatalytic quadruple cascade initiated by a Friedel-Crafts-type reaction is described. The (S)-diphenylprolinol trimethylsilyl ether catalyzed reaction yields highly functionalized cyclohexenecarbaldehydes bearing a 1,1-bis[4-(dialkylamino)phenyl]ethene moiety and three contiguous stereogenic centers. The reaction tolerates various functional groups and all products are obtained with very good diastereoselectivity and with virtually complete enantiomeric excess.

Kinetic resolution of racemic 5-alkylcyclohexenones via Pd(ii)-catalyzed 1,4-additions of arylboronic acids – access to trans 3-alkyl-5-arylcyclohexanones

Ferrocenyl phosphapalladacycle catalyzed kinetic resolution of racemic 5-alkylcyclohexenones via arylboronic acid addition provides access to optically active trans-3-alkyl-5-aryl cycloalkanones.

Synergistic Cu–amine catalysis for the enantioselective synthesis of chiral cyclohexenones

An unprecedented utilization of 1,3-acetonedicarboxylic acid as a 1,3-bis-pro-nucleophile and a reactive acetone surrogate in enantioselective catalysis has been reported.

The organocatalyzed domino Michael–aldol reaction revisited. Synthesis of enantioenriched 3-hydroxycyclohexanone derivatives by reaction of enals with α,α′-diaryl-substituted acetone

The reaction of enals with α,α′-diaryl-substituted acetones (pK_a > 18) catalyzed by (S)-1-(2-pyrrolidinylmethyl) pyrrolidine provides direct access to enantioenriched 2,5,6-trisubstituted-3-hydroxy cyclohexanones.

A highly enantioselective, organocatalytic [3+2]-cycloannulation reaction towards the de novo-synthesis of 1-cyclopentenyl-α-keto esters

A novel [3+2]-cycloannulation process produces cyclopentenes with good yields and excellent enantioselectivity via a domino-vinylogous Michael–Knoevenagel reaction.

Stereoselective synthesis of epoxyisoprostanes: an organocatalytic and “pot-economy” approach

An efficient and direct synthetic route to epoxyisoprostane EC methyl ester has been accomplished in 8 steps (10% overall yield) from readily available starting materials using a series of asymmetric organocatalytic reactions and one-pot operations.

Selecting reactions and reactants using a switchable rotaxane organocatalyst with two different active sites

The activation mode of a rotaxane-based organocatalyst with both secondary amine and squaramide catalytic units can be switched with acid or base. The macrocycle blocks whichever of the catalytic sites it is positioned over. The switchable rotaxane catalyst generates different products from a mixture of three building blocks according to the location of the macrocyclic ring in the rotaxane.

A new approach to asymmetric synthesis of infectocaryone

A new approach to the asymmetric synthesis of infectocaryone featuring a regioselective and stereoselective Diels–Alder reaction of an isomeric dienophile mixture is developed.

Recent progress on asymmetric organocatalytic construction of chiral cyclohexenone skeletons

Chiral cyclohex-2-enones are important intermediates in synthetic chemistry as well as in the life science industries. In this focus review, recent advances in the organocatalytic asymmetric synthesis of chiral cyclohex-2-enone skeletons are summarized. The reaction mechanisms are also briefly discussed.