Anti Stereoselectivity Research Articles

Phosphine-Catalyzed Vicinal Acylcyanation of Alkynoates.

Phosphine organocatalysis enabled vicinal acylcyanation of alkynoates with acyl cyanides to form acrylonitrile derivatives with a tetrasubstituted alkene moiety. The acyl and cyano groups were introduced at the α and β carbon atoms, respectively, of the C-C triple bond in the alkynoates with complete regioselectivity and high anti stereoselectivity. A variety of functional groups in the acyl cyanides and alkynoates were tolerated.

ChemInform Abstract: The Total Synthesis of Inostamycin A.

The first total synthesis of inostamycin A is described. With efficient and stereoselective synthetic routes to aldehyde 3 and ketone 4 developed through asymmetric aldol reactions, addition reactions and reduction, and with chiral building blocks, the two large fragments were coupled with remarkable anti stereoselectivity and efficiency by aldol condensation. The coupling reaction provided the complete carbon skeleton with all the requisite functional groups and stereogenic centers for inostamycin A. The two quaternary carbons at C20 and C16 of ketone 4 were elaborated in a highly stereocontrolled manner by addition reactions of the transmetallated 5 to ethyl ketone 6 and the transmetallated 7 to methyl ketone 8, respectively, in which the use of LaCl3 for transmetallation was critical for high coupling efficiency.

The Total Synthesis of Inostamycin A

The first total synthesis of inostamycin A is described. With efficient and stereoselective synthetic routes to aldehyde 3 and ketone 4 developed through asymmetric aldol reactions, addition reactions and reduction, and with chiral building blocks, the two large fragments were coupled with remarkable anti stereoselectivity and efficiency by aldol condensation. The coupling reaction provided the complete carbon skeleton with all the requisite functional groups and stereogenic centers for inostamycin A. The two quaternary carbons at C20 and C16 of ketone 4 were elaborated in a highly stereocontrolled manner by addition reactions of the transmetallated 5 to ethyl ketone 6 and the transmetallated 7 to methyl ketone 8, respectively, in which the use of LaCl3 for transmetallation was critical for high coupling efficiency.

The Total Synthesis of Inostamycin A

AbstractThe first total synthesis of inostamycin A is described. With efficient and stereoselective synthetic routes to aldehyde 3 and ketone 4 developed through asymmetric aldol reactions, addition reactions and reduction, and with chiral building blocks, the two large fragments were coupled with remarkable anti stereoselectivity and efficiency by aldol condensation. The coupling reaction provided the complete carbon skeleton with all the requisite functional groups and stereogenic centers for inostamycin A. The two quaternary carbons at C20 and C16 of ketone 4 were elaborated in a highly stereocontrolled manner by addition reactions of the transmetallated 5 to ethyl ketone 6 and the transmetallated 7 to methyl ketone 8, respectively, in which the use of LaCl3 for transmetallation was critical for high coupling efficiency.

Transition-metal-free direct anti-carboboration of alkynes with boronic acids to produce alkenylheteroarenes.

The transition-metal-free intermolecular direct 1,2-carboboration reaction of heteroarylacetylenes using boronic acids as reagents is achieved by utilizing tartaric acid as promoter. The reaction proceeds with excellent regioselectivity and anti stereoselectivity to afford boroxole frameworks. The resulting compounds are of use for the stereoselective preparation of polysubstituted alkenylheteroarenes.

Anti-selective vicinal silaboration and diboration of alkynoates through phosphine organocatalysis.

Trialkylphosphine organocatalysts have enabled anti-selective vicinal silaboration and diboration of the C-C triple bond in alkynoates to produce β-boryl-α-silyl acrylates and α,β-diboryl acrylates, respectively. The anti stereoselectivity was complete and robust. A variety of functional groups were tolerated in the alkynoates. The two vicinally installed heteroatom substituents of the β-boryl-α-silyl acrylates and α,β-diboryl acrylates could be differentiated and transformed in a stepwise manner, allowing the synthesis of a diverse array of unsymmetrical tetrasubstituted alkenes.

Synthesis of Lactones and Lactams from Vinylcyclopropane by Palladium- Catalyzed Nucleophilic Allylation

A palladium-catalyzed nucleophilic allylation of aldehydes with vinylcyclopropane in the presence of diethylzinc proceeded to provide homoallyl alcohols with anti stereoselectivity. Aldimines prepared from aldehyde and primary amines in situ underwent a similar nucleophilic allylation to give homoallylamines with syn stereoselectivity. The resulting homoallyl alcohols and homoallylamines could be converted by treatment with a tetranuclear zinc cluster into γ-vinyl-δ-valerolactones and γ-vinyl-δ-valerolactams, respectively.

Phosphine-catalyzed anti-carboboration of alkynoates with alkyl-, alkenyl-, and arylboranes.

We found that trialkylphosphine organocatalysts promoted unprecedented anti-carboboration of alkynoates with alkyl-, alkenyl-, or arylboranes to form β-boryl acrylates. The regioselectivity of the carboboration across the polar C-C triple bond exhibited inverse electronic demand, with the less electronegative B atom being delivered to the positively charged β carbon atom. The regioselectivity and the anti stereoselectivity were both complete and robust. In addition, the substrate scope was broad with excellent functional group compatibility.

Nano ZrO2: an efficient, recyclable, and inexpensive catalyst for diastereoselective three-component Mannich reactions

A facile procedure is developed for the three-component Mannich reactions of several heterocyclic, homocyclic, and acyclic ketones by using catalytic quantities of nano ZrO2. As a result, the starting ketones undergo rapid reactions with a variety of aromatic aldehydes and aniline derivatives at room temperature to produce stereoselectively high yields of the corresponding anti β-amino ketones. Interestingly, the catalyst could be recycled for several runs in a row without significant loss of its activity. The structure of the products was assigned based on their spectroscopic data and the anti stereoselectivity was confirmed by X-ray crystallography.

Selective Formation of Adjacent Stereocenters by Allylboration of Ketones under Mild Neutral Conditions

Allylboronic acids readily react with a broad variety of ketones, affording homoallylic alcohols with adjacent quaternary and tertiary stereocenters. The reaction proceeds with very high anti stereoselectivity even if the substituents of the keto group have a similar size. α-Keto acids react with syn stereoselectivity probably due to the formation of acyl boronate intermediates. The allylation reactions proceed without added acids/bases under mild conditions. Because of this, many functionalities are tolerated even with in situ generated allylboronic acids.

Mechanistic Studies of the CuH-Catalyzed Synthesis of α-Hydroxyallenes

The copper hydride catalyzed SN2′ reduction of propargyl oxiranes is an efficient method for the diastereoselective synthesis of α-hydroxyallenes. Herein, we represent a detailed computational study of this reaction using density functional theory (DFT), supported by kinetic investigations. The calculations partially validate the previously proposed reaction mechanism and explain the high anti stereoselectivity of the reaction arising from a diffusion-controlled Lewis acid activation of the epoxide–Cu–hydride complex.

Remarkable Stereoselectivity in Intramolecular Borono-Mannich Reactions: Synthesis of Conduramines

An unprecedented intramolecular Petasis condensation provides a novel approach to biologically important conduramines. The compounds are produced with an exclusive anti stereoselectivity for the newly created β-amino alcohol motif. The stereochemical outcome of the reaction is opposite to the one usually observed in the intermolecular reaction.

ChemInform Abstract: Vinylogous Mukaiyama—Michael Reactions Between 2‐Silyloxyfurans and Cyclic Enones or Unsaturated Oxo Esters.

AbstractIn the presence of SnCl4, cyclic enones and silyloxyfurans (II) undergo vinylogous Mukaiyama—Michael reactions to afford γ‐butenolides preferentially with anti stereoselectivity.

Biheteroaromatic diphosphine oxides-catalyzed stereoselective direct aldol reactions

A highly stereoselective direct aldol condensation of ketones to aromatic aldehydes was realized; the trichlorosilyl enolether generated in situ in the presence of tetrachlorosilane is activated by catalytic amounts of an enantiomerically pure biheteroaromatic phosphine oxide to react with aldehydes, coordinated as well as activated by the chiral cationic hypervalent silicon species. This Lewis acid-mediated Lewis base-catalyzed transformation allowed, starting from two carbonyl compounds, to directly synthesize β-hydroxy ketones generally with high anti stereoselectivity and up to 93% ee for the anti isomer.

ChemInform Abstract: Chelation Control in Metal-Assisted Aldol Addition Reactions of α -Halogenated Imide Enolates Leading to Predominantly Anti Stereoselectivity. An Example of a Stereocontrolled Darzens Reaction.

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Aerobic Oxidative Iodination of Organic Compounds with Iodide Catalyzed by Sodium Nitrite

AbstractSelective and efficient iodinations of organic compounds were achieved by an aerobic oxidative process catalyzed by sodium nitrite using potassium iodide in acidic media. Using the potasasium iodide (KI)/air/sodium nitrite (NaNO2; cat.)/sulfuric acid (H2SO4) iodinating system, activated and moderately deactivated aromatic compounds were exclusively or preferentially iodinated at the para position. In protic solvents ketones and 1,3‐dicarbonyl compounds were iodofunctionalized at the α carbonyl position, while in the case of aryl methyl ketones bearing an activated aromatic ring, the regioselectivity of iodination could be directed by the solvent used. In acetonitrile (MeCN) the aromatic ring was selectively iodinated, while in aqueous rethanol (EtOH) functionalization of the methyl carbon atom took place. Alkenes were transformed to vicinal iodohydrins or vicinal iodoalkoxy derivatives following Markovnikov‐type regioselectivity and anti stereoselectivity, while 1,2‐diiodoalkenes with preferentially E orientation were formed from alkynes.

Synthesis of Chiral 3-Pyrrolines from Propargyl Alcohols and N-Boc-amides

In this useful reaction sequence, the authors have first used a protocol for the enantioselective preparation of propargylic alcohols by the catalytic addition of alkynylzinc species to aldehydes. Then, a SN2′ substitution of an α-aminomethylcopper derivative provides aminomethylallenes with high anti stereoselectivity. Finally, their silver-catalyzed cyclization furnishes a new method of the enantioselective preparation of Δ3-pyrrolines, which are an important class of biologically active compounds.

Stereodivergent Formation of Alkenylsilanes: syn or anti Hydrosilylation of Alkynes Catalyzed by a Cyclopentadienylcobalt(I) Chelate Bearing a Pendant Phosphane Tether

AbstractThe hydrosilylation of alkynes is catalyzed by the di‐tert‐butylphosphanylethylcyclopentadienylcobalt chelate 1. While the reaction of internal alkynes exclusively affords syn hydrosilylation products with triethylsilane, the reaction with triethoxysilane shows predominant anti stereoselectivity. Reactions of terminal alkynes are less selective with triethylsilane and result in cyclotrimerization when triethoxysilane is used.

One-Pot Stereoselective Synthesis of anti 3-Alkyl and 3-Aryl-N-p-tosyl-aziridine-2-ketones and 3-Aryl-N-p-tosyl-aziridine-2-carboxylates.

For Abstract see ChemInform Abstract in Full Text.

Stereocontrolled Addition of Boron Enolates to trans α,β‐Aziridine Aldehydes. A New Route to anti‐1,2‐Amino Alcohols.

AbstractFor Abstract see ChemInform Abstract in Full Text.