C−N Axial Chiral Hypervalent Iodine Reagents: Catalytic Stereoselective α-Oxytosylation of Ketones

A simple synthesis of a library of novel C−N axially chiral iodoarenes is achieved in a three-step synthesis from commercially available aniline derivatives. C−N axial chiral iodine reagents are rarely investigated in the hypervalent iodine arena. The potential of the novel chiral iodoarenes as organocatalysts for stereoselective oxidative transformations is assessed using the well explored, but challenging stereoselective α-oxytosylation of ketones. All investigated reagents catalyse the stereoselective oxidation of propiophenone to the corresponding chiral α-oxytosylated products with good stereochemical control. Using the optimised reaction conditions a wide range of products was obtained in generally good to excellent yields and with good enantioselectivities.     

Stereocontrolled synthesis of novel 6′(α)-hydroxy carbovir analogues

This paper describes the racemic and stereoselective synthetic route for a novel 6′(α)-hydroxy-carbovir from a simple acyclic precursor, Solketal. The relative stereochemistry of the target nucleosides was successfully controlled by a sequential stereoselective glycolate Claisen rearrangement followed by a ring-closing metathesis (RCM). Adenine and cytosine were coupled using a Pd(0) catalyzed allylic alkylation strategy in a high regio- and stereoselective manner.     

A novel synthesis of amino-1,2-oxazinones as a versatile synthon for beta-amino acid derivatives

The radical addition-cyclisation of alpha, beta-unsaturated hydroxamates containing an oxime ether provides a novel method for the stereoselective synthesis of amino-1,2-oxazinones. Its synthetic utility is demonstrated by a stereoselective synthesis of beta-amino acid derivatives, such as alpha-alkyl-beta-amino-gamma-lactone and alpha,beta-disubstituted beta-lactam.     

The first total synthesis of (+/-)-scopadulin, an antiviral aphidicolane diterpene

[reaction: see text] The first total synthesis of (+/-)-scopadulin was accomplished by a stereoselective construction of a quaternary carbon at C-4, conversion of the hindered cyano group to a methyl group via our novel reaction for conversion of primary aliphatic amines into alcohols, and a highly chemo- and stereoselective methylation at C-16.     

Sulfinyl moiety as an internal nucleophile. 1. Efficient stereoselective synthesis of fragment a of cryptophycin 3

A novel, efficient, and stereoselective synthesis of fragment A of cryptophycin 3 is disclosed. The key step involves the regio- and stereoselective transformation of an unsaturated ester to a bromohydrin via anchimeric assistance by the sulfinyl group.     

A novel modification of the Ritter reaction: stereoselective synthesis of bridgehead-fused Δ2-norbornanethiazolines from thiocamphor and thiofenchone

An easy two-step route for the stereoselective synthesis of novel bridgehead-fused norbornanethiazolines from readily available natural camphor and fenchone is described. The key step of the synthetic route is the highly stereoselective trapping of 1-(trifluoromethylsulfonylthio)-2-norbornyl cations by nitriles followed by intramolecular cyclization, which constitutes a new modification of the Ritter reaction.     

Stereoselective synthesis of the enantiomer of the key fragment of crocacin

A novel, stereoselective synthesis of the enantiomer of alcohol 5 is disclosed. The key steps of the synthesis include mercuric trifluoroacetate promoted regio- and stereoselective hydration of an α,β-unsaturated ester, Frater-alkylation and use of morpholine derived amide for acylation.     

Synthetic studies on neomarinone: practical and efficient stereoselective synthesis of the side chain

A practical and efficient stereoselective synthesis of the side chain of neomarinone is reported. The synthesis was achieved in six steps (41% overall yield) from 2-methyl-2-cyclohexenone. The key step is a novel stereoselective 1,4-conjugate addition/enolate alkylation by an epoxide-opening reaction.     

A stereoselective route to 6-substituted pyrrolo-1,5-benzoxazepinones and their analogues

We developed a novel and convenient stereoselective path for the preparation of pyrrolo-1,5-benzoxazepinones (PBOs). This innovative route envisaged the employment of (−)-menthol as convenient chiral auxiliary and a key S_NAr for the stereoselective preparation of a tertiary aryl–alkyl ether. As a further advancement, we exploited this newly conceived synthetic route for the preparation of 2-substituted PBO analogues to either undergo biological evaluation themselves or give access to a variety of further functionalization options.     

Stereoselective biotransformations using fungi as biocatalysts

The development of novel biocatalytic methods is a continuously growing area of chemistry, microbiology, and genetic engineering due to the fact that biocatalysts are selective, easy-to-handle, and environmentally friendly. A wide range of reactions are catalyzed by microorganisms. Fungi can be considered as a promising source of new biocatalysts, mainly for chiral reactions. Chemo-, regio-, and stereoselective processes are very important in the synthesis of many chemical, pharmaceutical, and agrochemical intermediates; active pharmaceuticals; and food ingredients. This report reviews stereoselective reactions mediated by fungi, such as stereoselective hydroxylation, sulfoxidation, epoxidation, Baeyer–Villiger oxidation, deracemization, and stereo- and enantioselective reduction of ketones, published between 2000 and 2007.     

Lewis acid mediated endo-cyclisation of trimethylsilylmethylenecyclopropyl imines--a stereoselective route to indolizidines

Lewis acid mediated endo-cyclisation of trimethylsilylmethylenecyclopropyl imines provides a stereoselective route to indolizidines via a novel cascade sequence.     

Synthesis of the antifungal beta-1,3-glucan synthase inhibitor CANCIDAS (caspofungin acetate) from pneumocandin B0

A novel three-step synthesis of the highly functionalized antifungal agent CANCIDAS (caspofungin acetate, 2) is described, starting from the natural product pneumocandin B0 (1). The highlights of the synthesis include a stereoselective formation of a phenylthioaminal, a remarkable chemoselective, high-yielding, one-step borane reduction of a primary amide, and a stereoselective substitution of the phenylthioaminal with ethylenediamine producing 2 in a 45% overall yield.     

Facile Method for Stereoselective Synthesis of New Chiral (1R,4aR,8aR)‐1,3,4,4a,5,7,8,8a‐Octahydro‐2‐methylene‐naphthalene‐6‐one‐1‐propanenitrile,an Important Precursor of Solanapyrones

A novel and facile strategy for stereoselective synthesis of new chiral (1R,4aR,8aR)‐1,3,4,4a,5,7,8,8a‐octahydro‐2‐methylenenaphthalene‐6‐one‐1‐propanenitrile (8) by one‐pot stereoselective hydrogenation/acetalization and Beckmann fragmentation is described. Chiral octalone 8, an important precursor of solanapyrone, was obtained in good yield.     

Exploratory studies towards a total synthesis of the unusual bridged tetracyclic Lycopodium alkaloid lycopladine H

A strategy for a total synthesis of the structurally novel Lycopodium alkaloid lycopladine H has been investigated. Key steps that have been tested include: 1. a regioselective Diels-Alder cycloaddition of nitroethylene with an o-quinone ketal to produce the bicyclo[2.2.2]octane moiety of the alkaloid; 2. a stereoselective Henry reaction to generate the requisite functionality and configuration at C-5; 3. a stereoselective catalytic hydrogenation of a trisubstituted alkene to set the C-15 methyl configuration.     

Chiral trifluoromethylphosphines: a new stereoselective synthesis of Josiphos-type ligands containing two stereogenic phosphorus atoms

Intramolecular nucleophilic substitution of a trifluoromethyl group to form a 1,2-diphosphole derivative followed by the sequential addition of an alkylating agent and a carbanion are the key steps in the stereoselective synthesis of novel ferrocenyl diphosphines for asymmetric catalysis.     

Thin-Layer Chromatographic Enantioseparation of Ofloxacin and Zopiclone using Hydroxy-Propyl-Beta-Cyclodextrin as Chiral Selector and Thermodynamic Studies of Complexation

JPC – Journal of Planar Chromatography – Modern TLC - A novel economic thin-layer chromatographic procedure for stereoselective separation of racemic mixtures of each of zopiclone and...     

Total syntheses of (-)-alpha-kainic acid and (+)-alpha-allokainic acid via stereoselective C-H insertion and efficient 3,4-stereocontrol

Reported herein is a novel approach to the total syntheses of (-)-alpha-kainic acid and (+)-alpha-allokainic acid, where the stereochemistries on C(2), C(3), and C(4) of the pyrrolidine core were introduced efficiently and selectively. A regio- and stereoselective C-H insertion reaction was utilized to prepare the gamma-lactam as an intermediate. A Michael-type cyclization of phenylsulfone with a conjugated acetylenic ketone was developed to prepare the tricyclic ketone as a key intermediate for (-)-alpha-kainic acid. Subsequently, a stereoselective dephenylsulfonylation was carried out successfully to secure the cis relationship at C(3) and C(4) centers. An unprecedented acetylation on the phenylsulfone, followed by a stereoselective dephenylsulfonylation, secured the trans relationship at C(3) and C(4) centers in (+)-alpha-allokainic acid.     

Total synthesis of reveromycin B

[formula: see text] The stereoselective total synthesis of reveromycin B (2), a novel polyketide-type antibiotic, has been accomplished.     

A novel and stereospecific synthesis of (+)-preussin

A novel and stereospecific approach to (+)-preussin that would permit the synthesis of analogs for structure activity relationship studies, is disclosed. The key step includes the regio- and stereoselective elaboration of a bromohydrin via intramolecular sulfinyl group participation.     

The diverse chemistry of oxazol-5-(4H)-ones

The assembly of structurally diverse scaffolds via substrate controlled diversity oriented synthesis (DOS) has proven to be an effective tool in the discovery of novel biologically important compounds. This tutorial review aims to summarize some of the more recent applications of oxazolones as a general template for the stereoselective syntheses of amino acids and heterocyclic scaffolds. A brief introduction covers a short history, nomenclature and general reactivity of oxazolones. The main body of this tutorial review highlights several applications of oxazolones as starting blocks for the diverse and stereoselective synthesis of amino acids, oxazoles, beta-lactams, pyrroles, imidazolines, pyrrolines, and imidazoles.