Organocatalytic Process Research Articles

ChemInform Abstract: N‐Heterocyclic Carbene Catalyzed Cascade Epoxide‐Opening and Lactonization Reaction for the Synthesis of Dihydropyrone Derivatives.

N-Heterocyclic carbene was employed as an efficient organic catalyst to catalyze a cascade epoxide-opening and lactonization reaction. This organocatalytic process could transform various readily accessible γ-epoxy-α,β-enals into dihydropyrone derivatives in good to excellent yields.

Silica-supported 5-(pyrrolidin-2-yl)tetrazole: development of organocatalytic processes from batch to continuous-flow conditions

5-(Pyrrolidin-2-yl)tetrazole functionalized silica prepared by photoinduced thiol–ene coupling is packed into a short stainless steel column. The resulting packed-bed microreactor is conveniently heated to perform environmentally benign continuous-flow aldol reactions with good stereoselectivities, complete conversion efficiencies, and long term stability of the packing material.

Organocatalytic Asymmetric Additions to meso‐Anhydrides and Azlactones

AbstractThis review charts the recent progress of two related, yet distinct organocatalytic processes: the desymmetrisation of meso‐anhydrides and the dynamic kinetic resolution of azlactones. Driven by recent advances in catalyst design, both these processes have undergone something of a renaissance in recent years and are now becoming very powerful and versatile synthetic methodologies. The material is presented in a critical fashion and the material is organised by reaction type and catalyst class.

ChemInform Abstract: Oxazolones in Organocatalysis, New Tricks for an Old Reagent

AbstractReview: [40 refs.]

Oxazolones in Organocatalysis, New Tricks for an Old Reagent

Oxazolones or azlactones are among the most-common starting materials for the synthesis of quaternary amino acids. Since the seminal works of Steglich and co-workers until the recent examples from Ooi and co-workers, azlactones have been the focus of intense research. Oxazolones are also widely used in organometallic chemistry; however, with the "renaissance" of organocatalysis, this reagent has emerged as an important starting material for a broad range of new organocatalytic asymmetric methodologies. In this Focus Review, we aim to cover all of these new organocatalytic methodologies. We begin by discussing the dynamic kinetic resolution reactions developed with azlactones. Then, we disclose the organocatalytic rearrangements. Finally, we focus on the use of oxazolones as nucleophiles in organocatalytic processes.

N-Heterocyclic carbene-catalyzed cascade epoxide-opening and lactonization reaction for the synthesis of dihydropyrone derivatives

N-Heterocyclic carbene was employed as an efficient organic catalyst to catalyze a cascade epoxide-opening and lactonization reaction. This organocatalytic process could transform various readily accessible γ-epoxy-α,β-enals into dihydropyrone derivatives in good to excellent yields.

An organocatalytic approach to enantiomerically enriched α-arylcyclohexenones and cyclohexanones

The presence of a p-nitrophenyl group converts acetone into an excellent and versatile nucleophile in organocatalytic processes, able to react with α,β-unsaturated aldehydes affording β-substituted α-arylcyclohexenones via a Michael reaction/aldol reaction/dehydration sequence, which occurs in good yields, ee up to 96% and complete diastereoselectivity. The resulting compounds are excellent synthons for the diastereoselective preparation of a variety of synthetically useful polysubstituted cyclohexanones and derivatives.

Organocatalyst-mediated Aldol–Robinson Cascade Reactions: A Convenient Synthesis of Substituted Cyclohex-2-enones

Abstract A convenient organocatalytic process for the chemoselective synthesis of substituted cyclohex-2-enones was developed. The cascade reaction involves a remarkable Michael addition of an acyclic ketone-based enamine onto unmodified enones. The enamine-mediated aldol–Robinson cascade reactions of aromatic and aliphatic aldehydes with acetone produced substituted cyclohex-2-enones in moderate to high yields under mild reaction conditions.

ChemInform Abstract: Sulfones: New Reagents in Organocatalysis

AbstractReview: 76 refs.

ChemInform Abstract: Computational Studies of Organocatalytic Processes Based on Hydrogen Bonding

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxidative Amidation and Azidation of Aldehydes by NHC Catalysis

N-heterocyclic carbene catalyzed oxidative amidations of various aldehydes to the corresponding hexafluoroisopropylesters by using the readily available organic oxidant A are described. The hexafluoroisopropylesters prepared in situ are shown to be highly useful active esters for amide bond formation. In addition, oxidative azidation of aldehydes is presented. These mild organocatalytic processes do not use any transition metal.

Synergistic organocatalysis in the kinetic resolution of secondary thiols with concomitant desymmetrization of an anhydride

Kinetic resolution is an important method for the separation of racemates into their component enantiomers. Thiols are precursors to a variety of organosulfur compounds, with high utility in both chemistry and chemical biology, yet there is a surprising dearth of methodologies for their direct and efficient catalytic kinetic resolution. Here, we demonstrate an organocatalytic process involving the highly enantioselective desymmetrization of an achiral electrophile with the simultaneous kinetic resolution of a racemic thiol. The preparative potential of the methodology is exemplified by the synthesis of a drug precursor antipode in excellent yield and enantioselectivity as a by-product of a process that also resolves a sec-thiol substrate with a selectivity of S = 226 (that is, both thiol antipodes produced in >95% ee at 51% conversion). In a second example a racemic sec-thiol representing the stereocentre-containing core of the anti-asthma drug (R)-Montelukast was resolved with synthetically useful selectivity under mild conditions.

Sulfones: new reagents in organocatalysis

The development of new asymmetric methodologies that afford different structures in an enantioselective fashion is one of the most exciting goals for chemists nowadays. In this subject, lately, the use of sulfones has become a fast growing field. From the works of Tan and Shibata until the last works of Palomo, sulfones have demonstrated their versatility and power in organocatalytic asymmetric reactions. Moreover, the easy removal of sulfones with Mg or Hg/Na makes this group a perfect choice to afford easily naked alkyls. Remarkably, bissulfones can be used as nucleophiles or electrophiles, being vinyl sulfones excellent electrophiles, while bismethylensulfones derivatives such as fluoro are excellent nucleophiles. This double possibility has been studied by several research groups, leading to new methodologies that allow obtaining formally simple alkylation in an enantioselective fashion, by using organocatalysis. The aim of this tutorial review is to summarize the last trends in the use of sulfones in organocatalytic processes, giving a complete scenario of these new reagents.

ChemInform Abstract: Highly Stereoselective One‐Pot Synthesis of Bicyclic Isoxazolidines with Five Stereogenic Centers by an Organocatalytic Process.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

New Access to Trisubstituted 3-Pyrrolines under Phosphine Catalysis

Conjugated dienes, properly activated by electron-withdrawing groups on both ends, are shown to be suitable substrates for phosphine-promoted organocatalytic processes. Their reactions with imines, under phosphine catalysis, afford a new and efficient synthetic approach to functionalized 3-pyrrolines.

Highly Stereoselective One‐Pot Synthesis of Bicyclic Isoxazolidines with Five Stereogenic Centers by an Organocatalytic Process

Highly Stereoselective One‐Pot Synthesis of Bicyclic Isoxazolidines with Five Stereogenic Centers by an Organocatalytic Process

Highly Stereoselective One‐Pot Synthesis of Bicyclic Isoxazolidines with Five Stereogenic Centers by an Organocatalytic Process

Highly Stereoselective One‐Pot Synthesis of Bicyclic Isoxazolidines with Five Stereogenic Centers by an Organocatalytic Process

Enantio- and Diastereoselective Asymmetric Addition of 1,3-Dicarbonyl Compounds to Nitroalkenes in a Doubly Stereocontrolled Manner Catalyzed by Bifunctional Rosin-Derived Amine Thiourea Catalysts

Starting from commercially available natural rosin derivatives, a class of bifunctional rosin-derived amine thiourea catalysts were designed and synthesized. The doubly stereocontrolled asymmetric addition of a variety of 1,3-dicarbonyl compounds to nitroalkenes was investigated. These rosin-derived chiral thioureas have been shown to serve as effective catalysts for this double-sterecontrolled organocatalytic process by the investigation of the efficacy of the thiourea catalysts in comparison with other thiourea catalysts reported. In addition, these chiral thiourea ligands are easily available. Furthermore, the rosin-derived tertiary amine-thiourea was also revealed to be highly efficient for construction of contiguous stereogenetic centers containing an asymmetric quaternary carbon by the Michael reaction of alpha-substituted beta-ketoesters to nitroalkenes.

Catalysts Based on Amino Acids for Asymmetric Reactions in Water

Asymmetric organometallic and organocatalytic processes in aqueous systems are currently of great interest. A few years ago, only a few practitioners studied the subject; now organic reactions in water have become one of the most exciting research areas. The quest to identify water-compatible catalysts has evoked an intense search for new possibilities. Following nature's lead, the application of amino acids as sources of chiral information seems particularly promising for aqueous systems. Herein we provide an overview of very recent advances in the area of asymmetric catalysis in water with amino acids and their derivatives as effective catalysts or essential components of catalysts.

An Efficient Enantioselective Method for Asymmetric Friedel–Crafts Alkylation of Indoles with α,β‐Unsaturated Aldehydes

Abstractmagnified imageThe Lewis base‐Lewis base bifunctional catalytic system has been developed and successfully applied to the asymmetric Friedel–Crafts alkylation of indoles with α,β‐unsaturated aldehydes. The reactions are promoted by chiral diphenylprolinol trimethylsilyl ether in the presence of triethylamine. By this protocol, optically active 3‐substituted indoles can be obtained in an organocatalytic process that is free of Lewis or protic acid in high yields with up to 98% ee. Besides, this reaction could be carried out on a gram scale without any loss in the enantioselectivity.