A stereospecific total synthesis of (±)-epipentenomycin I, (±)-epipentenomycin II and (±)-epipentenomycin III

A highly efficient, stereospecific synthesis of the epimeric pentenomycins is reported utilizing the stereospecific addition of OsO₄ to substituted cyclopentenes.     

Interaction between Divalent Copper Fluoride and Carboxamide Group Enabling Stereoretentive Fluorination of Tertiary Alkyl Halides

Herein, we report a copper-catalyzed stereospecific fluorination involving CsF and α-bromocarboxamides as tertiary alkyl sources that, unlike traditional stereospecific routes involving stereoinversive S_N2 reactions, proceeds with retention of stereochemistry. The developed stereospecific Cu-catalyzed reaction is among the most efficient methods for synthesizing fluorinated molecules that possess highly congested stereogenic carbon centers. Mechanistic studies revealed that the combined reactivity of CuF₂ and Cs salt is essential for completing the catalytic cycle. Our catalytic system underwent fluorination exclusively with tertiary alkyl bromides and did not react with primary alkyl bromides, indicating that this stereospecific fluorination methodology is suitable for synthesizing fluorinated building blocks possessing stereo-defined F-containing tertiary carbon stereogenic center.     

A stereospecific phosphonium ylide-salt coupling reaction

The stereospecific formation of a phosphonium ylide-salt via the stereospecific coupling of an allylic phosphonium ylide with the corresponding phosphonium salt is described.     

The sulfinyl moiety as an internal nucleophile. Part 8: Efficient, stereospecific synthesis of (+)-polyoxamic acid

A straightforward and stereospecific synthesis of (+)-polyoxamic acid is disclosed. The key step of the synthesis involves the regio- and stereospecific bromohydration of an olefin via intramolecular participation by the sulfinyl group.     

Regio- and stereospecific syntheses of syn- and anti-1,2-imidazolylpropylamines from the reaction of 1,1'-carbonyldiimidazole with syn- and anti-1,2-amino alcohols

The regio- and stereospecific conversion of syn- and anti-1,2-amino alcohols to their respective syn- and anti-1,2-imidazolylpropylamines via treatment with 1,1'-carbonyldiimidazole is described. The rationale behind the regio- and stereospecific nature as well as the generality of the reaction is discussed.     

Stereoselective Synthesis of Trisubstituted Vinylboronates from Ketone Enolates Triggered by 1,3‐Metalate Rearrangement of Lithium Enolates

An unprecedented stereoselective synthesis of trisubstituted vinylboronates is reported to proceed by direct borylation of lithium ketone enolates under transition‐metal‐free conditions. The stereospecific C?O borylation of lithium enolates was triggered by a carbonyl‐induced 1,3‐metalate rearrangement via a C‐bound boron enolate. DFT calculations and control experiments revealed that the stereoselectivity is controlled by sterics. A variety of stereospecific trisubstituted vinylboronates, together with several tetrasubstituted vinylboronates, were conveniently synthesized with the newly developed methodology. Based on the transformation of stereospecific vinylboronate, a single isomer of Dienestrol was efficiently obtained.     

3-甲基-5-苯砜基-3E-戊烯-1-醇的立体专一性合成

3-甲基-5-苯砜基-3E-戊烯-1-醇(1)是合成某些萜类化合物的重要中间体.它具有反式烯丙基苯砜基双键.Julia等曾报道用含砜基的环丙基醇的开环重排反应来实现这类化合物的立体选择性合成,但其开环前体不易得到.本文以4-羟基-2-丁酮(2)为起始原料,经4步反应立体专一性地合成了标题化合物1.合成路线短、操作简便、易于大量制备.合成路线用方程式表示如下:     

Stereospecific synthesis of hydroxylated steroid side chains. Synthesis of 25,28-dihydroxy-7,8-dihydroergosterol and its c-24 epimer via [2,3] sigmatropic rearrangement.

An efficient, stereospecific synthesis of hydroxylated ergosterol and C-24 epi-ergosterol side chains has been developed using a C-20 keto-steroid as starting material. The side chain is elaborated via stereoselective hydroboration, asymmetric reduction and a stereospecific [2, 3] sigmatropic rearrangement.     

Stereospecific assignments of protein NMR resonances based on the tertiary structure and 2D/3D NOE data

In many cases of protein structure determination by NMR a high-quality structure is required. An important contribution to structural precision is stereospecific assignment of magnetically nonequivalent prochiral methylene and methyl groups, eliminating the need for introducing pseudoatoms and pseudoatom corrections in distance restraint lists. Here, we introduce the stereospecific assignment program that uses the resonance assignment, a preliminary 3D structure and 2D and/or 3D nuclear Overhauser effect spectroscopy peak lists for stereospecific assignment. For each prochiral group the algorithm automatically calculates a score for the two different stereospecific assignment possibilities, taking into account the presence and intensity of the nuclear Overhauser effect (NOE) peaks that are expected from the local environment of each prochiral group (i.e., the close neighbors). The performance of the algorithm has been tested and used on NMR data of alpha-helical and beta-sheet proteins using homology models and/or X-ray structures. The program produced no erroneous stereospecific assignments provided the NOEs were carefully picked and the 3D model was sufficiently accurate. The set of NOE distance restraints produced by nmr2st using the results of the SSA module was superior in generating good-quality ensembles of NMR structures (low deviations from upper limits in conjunction with low root-mean-square-deviation values) in the first round of structure calculations. The program uses a novel approach that employs the entire 3D structure of the protein to obtain stereospecific assignment; it can be used to speed up the NMR structure refinement and to increase the quality of the final NMR ensemble even when no scalar or residual dipolar coupling information is available.     

Enantiospecific synthesis of optically active cyclohexylidene bromomethanes

Optically pure cyclohexylidene bromomethanes were prepared by stereospecific bromination alpha to a chiral sulfoxide, followed by the stereospecific pyrolytic elimination of the sulfoxide moiety.     

Base-mediated stereospecific synthesis of aryloxy and amino substituted ethyl acrylates

The stereospecific synthesis of aryloxy and amino substituted E- and Z-ethyl-3-acrylates is of interest because of their potential in the polymer industry and in medicinal chemistry. During work on a copper-catalyzed cross-coupling reaction of ethyl (E)- and (Z)-3-iodoacrylates with phenols and N-heterocycles, we discovered a very simple (nonmetallic) method for the stereospecific synthesis of aryloxy and amino substituted acrylates. To study this long-standing problem on the stereoselectivity of aryloxy and amino substituted acrylates, a series of O- and N-substituted nucleophiles was allowed to react with ethyl (E)- and (Z)-3-iodoacrylates. Screening of different bases indicated that DABCO (1,4-diazabicyclo[2.2.2]octane) afforded successful conversion of ethyl (E)- and (Z)-3-iodoacrylates into aryloxy and amino substituted ethyl acrylates in a stereospecific manner. Herein are the details of this DABCO-mediated stereospecific synthesis of aryloxy and amino substituted E- or Z-acrylates.     

磷脂的不对称合成研究进展

本文综述了磷脂不称合成方面的研究进展, 包括半合成法和化学合成法。着重讨论了利用不对称反应和手性前体合成不对称甘油型磷脂骨架的方法。     

Total synthesis of (-)-senepodine G and (-)-cermizine C

An efficient, stereospecific synthesis of the alkaloids senepodine G (2) and cermizine C (1) has been completed using the BF3.Et2O-promoted stereospecific addition of Me2CuLi to alpha,beta-unsaturated lactam 6 to provide lactam 3, the addition of MeMgBr followed by HCl to convert 3 to senepodine G (2) (six steps, 40% overall yield), and the stereospecific NaBH4 reduction of 2 to give cermizine C (1) (seven steps, 40% overall yield).     

Stereospecific allylsilane reactions: a total synthesis of dihydronepetalactone

A stereospecific synthesis of allylsilanes and their stereospecific reaction with peracid are used to prepare the endo-prop-1-enylnorbornenol (6), a substrate for an oxy-Cope rearrangement leading eventually to dihydronepetalactone (10) with complete stereocontrol.     

Novel 6-position modified 1-thioalkyl-lincosamines

A general method for the synthesis of 6-position modified lincosamines via stereospecific nucleophilic addition to readily available galactose 6-nitrone has been developed. A new route for the stereospecific installation of thioalkyl groups at the 1-position was also developed. These methods allow access to a variety of new derivatives of antibacterial lincosamides.     

A combined time-resolved and stereospecific deuterium labelling study of the elimination of methanol from the molecular ion of methoxycyclohexane

It is shown by field ionization kinetics in combination with both site-specific and stereospecific D-labelling that the loss of a molecule of methanol from the molecular ion of methoxycyclohexane can occur via 1,4- and 1,3-eliminations. The 1,4-elimination predominates at molecular ion lifetimes of ≥10^?10.1 s. It is found that ～19% of this reaction channel corresponds to a stereospecific cis-elimination, whereas the remaining 81% is only site-specific. At molecular ion lifetimes of between 10^?10 and 10^?9 s, a very sudden increase of the 1,3-elimination is observed at the expense of the 1,4-elimination. A stereospecific loss of methanol, however, is not observed at all for the 1,3-elimination within the limits of error. Possible intermediates and reaction pathways, which can account for the observations made, are discussed.     

Metal-catalyzed coupling reactions on an olefin template: the total synthesis of Bupleurynol

The naturally occurring polyacetylene Bupleurynol was synthesized in a convergent and stereospecific manner using a series of metal-mediated cross-coupling reactions. The synthesis demonstrates the utility of using a di-functional olefin template for the stereospecific synthesis of a disubstituted alkene product and its elaboration to a natural product target.     

Synthese stereospecifique de l'ester methylique de l'acide amino-2 oxo-8 epoxy-9,10 decanoique (2s,9r) N - protege.

The first stereospecific synthesis of methyl (2S,9R) N-tBOC 2-amino 8-oxo 9,10-epoxydecanoate has been carried out by using two steps allowing a chirality control: a stereospecific alkylation of the Schiff base 4 and Sharpless epoxidation of the allylic alcohol 6.     

Stereospecific total synthesis of cycloeudesmol

A stereospecific sequence from the allylic alcohol $\text{3}$ to the new antibiotic, cycloeudesmol $\text{2}$, in 9 steps (21.7% overall yield) is described. The key stereospecific construction of the bicyclo [3.1.0] hexane system was conveniently achieved by an olefin-ketocarbene cyclization reaction.     

A new method for the stereospecific synthesis of ether phospholipids. Preparation of the amide analog of platelet-activating factor and related derivatives

A novel stereospecific synthesis of biologically active ether-phospholipids is reported.