An alkyne hydrosilylation-oxidation strategy for the selective installation of oxygen functionality

Alkynes bearing propargylic, homopropargylic, and bishomopropargylic hydroxyl groups are shown to serve as precursors for ketone or alpha-hydroxy ketone functionality. The approach hinges on the intermediacy of vinylsilanes created through regioselective hydrosilylation catalyzed by the complex [Cp*Ru(MeCN)3]PF6. Several oxidative pathways of linear and cyclic vinylsilanes are studied, and the possibility of diastereoselective epoxidation of cyclic vinylsilanes is demonstrated. The sequences constitute the equivalent of stereoselective aldol, homo-aldol, and bishomo-aldol type processes. The method is applied to a short synthesis of the piperidine alkaloid, spectaline.     

The effect of substituents at silicon on the cross-metathesis of trisubstituted vinylsilanes with olefins

Efficient cross-metathesis of vinylsilanes, carrying a large spectrum of different substituents at silicon, with various olefins in the presence of the first and second generation Grubbs catalyst and Hoveyda–Grubbs catalyst is described. On the basis of the results of equimolar reactions of vinylsilanes with ruthenium alkylidene complexes and experiments with deuterium-labelled reagents, a general, metallacarbene mechanism for the cross-metathesis of trisubstituted vinylsilanes with olefins has been suggested. Reaction was proved to be a valuable method for synthesis of unsaturated organosilicon derivatives.     

A synthesis of multisubstituted vinylsilanes via ynolates: stereoselective formation of beta-silyl-beta-lactones followed by decarboxylation

(Z)-Selective synthesis of multisubstituted vinylsilanes was achieved by stereoselective protonation or alkylation of beta-silyl-beta-lactone enolates, prepared by cycloadditions of acylsilanes with ynolates, followed by decarboxylation.     

Expedient enantioselective synthesis of the δ4-oxocene cores of (+)-laurencin and (+)-prelaureatin (‡)

An expedient enantioselective synthesis of the Δ(4)-oxocene cores present in (+)-laurencin and (+)-prelaureatin was accomplished in eight steps via a novel one-pot regio- and stereoselective ring cyclization-fragmentation-expansion cascade from the tetrahydrofuran precursors which were prepared by stereocontrolled cyclization from vinylsilanes. This process is highlighted by an intramolecular oxo-carbenoid insertion and a β-silyl fragmentation sequence.     

The regio- and stereochemical course of reductive cross-coupling reactions between 1,3-disubstituted allenes and vinylsilanes: synthesis of (Z)-dienes

In investigations aimed at exploring the potential of disubstituted allenes in stereoselective synthesis, we report studies that explore the reductive cross-coupling reaction of vinylsilanes with a range of substituted allenes. Regiochemical control is attained by employing allenic alkoxides, where the proximal heteroatom dictates the site-selectivity in a process that proceeds by net formal metallo-[3,3] rearrangement (directed carbometalation/elimination). Stereoselectivity in these reactions is complex, with both the nature of allene substitution and relative stereochemistry of the substrate impacting the stereoselective generation of each alkene of a substituted 1,3-diene.     

Acid-catalyzed cyclization of vinylsilanes bearing an amino group. Stereoselective synthesis of pyrrolidines

[reaction: see text] In the presence of an acid catalyst, vinylsilanes 1 bearing an amino group protected by an electron-withdrawing group were smoothly cyclized to 2-(silylmethyl)pyrrolidines 2. This cyclization was utilized for the stereoselective synthesis of 2,n-disubstituted pyrrolidines (n = 3-5). The cyclized products could be converted to the corresponding alcohols by oxidative cleavage of the carbon-silicon bond with TBAF and H2O2.     

The sulfinyl moiety as an internal nucleophile. 2. Stereoselective synthesis of (-)-galantinic acid via 1,3-asymmetric induction

A stereoselective synthesis of (-)-galantinic acid is disclosed. The key steps include hydrolytic kinetic resolution of a racemic epoxide and regio- and stereoselective heterofunctionalization of an olefin, using a pendant sulfinyl group as the nucleophile. The participation of the sulfinyl group was unambiguously proven by conducting the reaction in the presence of H(2)(18)O.     

Diversity-oriented synthesis of multisubstituted olefins through the sequential integration of palladium-catalyzed cross-coupling reactions. 2-pyridyldimethyl(vinyl)silane as a versatile platform for olefin synthesis.

A novel strategy for the diversity-oriented synthesis of multisubstituted olefins, where 2-pyridyldimethyl(vinyl)silane functions as a versatile platform for olefin synthesis, is described. The palladium-catalyzed Heck-type coupling of 2-pyridyldimethyl(vinyl)silanes with organic iodides took place in the presence of Pd2(dba)3/tri-2-furylphosphine catalyst to give beta-substituted vinylsilanes in excellent yields. The Heck-type coupling occurred even with alpha- and beta-substituted 2-pyridyldimethyl(vinyl)silanes. The one-pot double Heck coupling of 2-pyridyldimethyl(vinyl)silane took place with two different aryl iodides to afford beta,beta-diarylated vinylsilanes in good yields. The palladium-catalyzed Hiyama-type coupling of 2-pyridyldimethyl(vinyl)silane with organic halides took place in the presence of tetrabutylammonium fluoride to give di- and trisubstituted olefins in high yields. The sequential integration of Heck-type (or double Heck) coupling and Hiyama-type coupling produced the multisubstituted olefins in regioselective, stereoselective, and diversity-oriented fashions. Especially, the one-pot sequential Heck/Hiyama coupling reaction provides an extremely facile entry into a diverse range of stereodefined multisubstituted olefins. Mechanistic considerations of both Heck-type and Hiyama-type coupling reactions are also described.     

Modular and stereoselective formal synthesis of MeBmt, an unusual amino acid constituent of cyclosporin A

A convergent, flexible and stereoselective formal synthesis of MeBmt, the nonproteinogenic amino acid constituent of cyclosporin A is disclosed. The sulfinyl moiety has been exploited as the internal nucleophile to stereo- and regioselectively functionalize an allylic carbamate.     

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.     

An asymmetric synthesis of (+)-desoxoprosophylline

An efficient synthesis of (+)-desoxoprosophylline is described. The key steps in the reaction sequence include the preparation of an N-Cbz-sulfilimine from the corresponding sulfoxide using the Burgess reagent, regio- and stereoselective hetero-functionalization of an alkene using the pendant sulfilimine as the nucleophile and a stereoselective amidomercuration to form the cis-2,6-disubstituted piperidine ring.     

The sulfinyl moiety as an intramolecular nucleophile. Part 3: Synthesis of (−)-muricatacin

A short, efficient and highly stereoselective synthesis of (−)-(R,R)-muricatacin is reported. The key steps include a highly diastereoselective reduction of a β-ketosulfoxide to a β-hydroxy sulfoxide, regio- and stereoselective bromohydration of an olefin employing the sulfinyl group as an internal nucleophile and chemoselective reduction of a double bond in the presence of a halogen atom.     

N-Cbz sulfilimines as valuable intramolecular nucleophiles for the stereoselective synthesis of (−)-deoxocassine and (+)-desoxoprosophylline

N-Cbz sulfilimine, prepared from the corresponding sulfoxide using the Burgess reagent, has been employed as an intramolecular nucleophile for the regio- and stereoselective preparation of a bromo-carbamate from an alkene. The bromo-carbamate has been utilized as an advanced common synthon for the synthesis of deoxocassine and desoxoprosophylline employing the ene and amidomercuration as key reactions.     

Regioselective and stereoselective synthesis of tetrahydrofurans from a functionalized allylic silane and an aldehyde via formal [3+2]-cycloaddition reaction

Allylsilanes are known as useful reagents for the stereoselective formation of ring systems. Previous studies have shown that tetrahydrofurans can be constructed via formal [3+2]-cycloadditions of aldehydes and allylsilanes. A new challenge is to understand the intermediate, after a nucleophile attacks a carbonyl activated by the Lewis acid, in which two silyl-protected alkoxy groups with chemical equivalency could undergo formal cycloaddition reaction to afford a disubstituted and/or a trisubstituted tetrahydrofuran. Preparation of the protected α-hydroxy aldehyde and a functionalized allylic silane is discussed, as well as their formal cycloaddition reaction to form tetrahydrofurans.     

A stereoselective synthesis of the hexahydroazepine core of (−)-balanol

A stereoselective synthesis of the hexahydroazepine core of (−)-balanol is described. The key step of the route includes the bromosulfonamidation of an olefin using the intramolecular sulfilimine group as the nucleophile and the Pummerer ene reaction.     

Reactions between Grignard reagents and heterocyclic N-oxides: stereoselective synthesis of substituted pyridines, piperidines, and piperazines

In this perspective we discuss the recent developments of stereoselective synthesis of substituted pyridines, piperidines, and piperazines from cheap and commercially readily available starting materials. Pyridine N-oxides and pyrazine N-oxides are reacted with alkyl, aryl, alkynyl and vinyl Grignard reagents to give a diverse set of heterocycles in high yields. Optically active substituted piperazines are obtained by an asymmetric reaction from pyrazine N-oxides using sparteine as chiral ligand. In addition, a stereoselective synthesis of dienal-oximes from the reaction between pyridine N-oxides and Grignard reagents is presented, which results in a useful intermediate for the synthesis of a diverse set of compounds.     

Copper-catalyzed tethered aziridination of unsaturated N-tosyloxy carbamates

Aziridines were formed by copper-catalyzed intramolecular nitrene addition to alkenes. The carbamate group was used as the tether between the alkene and the nitrene. Subsequent nucleophilic attack of the aziridine was accomplished using RSH, R2NH, N3-, or ROH as the nucleophile. This addition was found to be regio- and stereoselective. This methodology has been used to demonstrate its utility in the regio- and stereoselective synthesis of a 1,2-diamino-3-hydroxycyclohexane. This substitution pattern is found in natural products such as Tamiflu.     

立体选择性还原的硼试剂及其在手性药物合成中的应用

硼试剂在药物化学合成中广泛应用. 综述了可参与立体选择性还原反应的手性硼试剂、烷基硼试剂和硼氢化钠衍生物在手性药物合成中的应用, 并讨论这些试剂用于工业化生产的潜力.     

New access to 1-deoxynojirimycin derivatives via azide-alkene cycloaddition

The synthesis of 1-deoxynojirimycin (DNJ) derivatives is described from D-glucono-delta-lactone. The DNJ derivatives were obtained via a sequence that included a stereoselective intramolecular Huisgen reaction, decomposition to an aziridine, and its subsequent reaction with a nucleophile. Minimization of allylic strain in the transition state accounts for the stereoselectivity of the cycloaddition reaction.     

Stereoselective synthesis of α-hydroxy-β-amino acid derivatives from β-hydroxy-γ,δ-unsaturated sulfilimine

The first report on the use of N-sulfinyl benzylcarbamate for the preparation of N-Cbz sulfilimine from the corresponding sulfoxide is reported. The sulfilimine moiety is utilized as an intramolecular nucleophile for the regio- and stereoselective heterofunctionalization of an alkene to furnish a bromo carbamate which is used as a key advanced intermediate in the synthesis of representative α-hydroxy-β-amino acid derivatives.