Aldol reactions with trifluoroacetophenones as acceptors yield chiral α-aryl, α-trifluoromethyl tertiary alcohols, valuable intermediates in organic synthesis. Of the various organocatalysts examined, Singh's catalyst [(2S)-N-[(1S)-1-hydroxydiphenylmethyl-3-methylbutyl]-2-pyrrolidinecarboxamide] was found to efficiently promote this organocatalytic transformation a highly enantioselective manner. Detailed reaction monitoring ((19)F-NMR, HPLC) showed that, up full conversion, catalytic...

As reported by Scheidt and Bode in 2005, sterically nonencumbered α,β-enals are readily converted to saturated esters the presence of alcohols N-heterocyclic carbene catalysts, e.g., benzimidazolylidenes or triazolylidenes. However, substituents at α- β-position α,β-enal substrate typically not tolerated, thus severely limiting spectrum. On basis our earlier mechanistic studies, a set N-Mes- N-Dipp-substituted 1,2,4-triazolium salts were synthesized evaluated as (pre)catalysts redox...

Abstract We report the discovery that simple carboxylic acids, such as benzoic acid, boost activity of N‐heterocyclic carbene (NHC) catalysts in oxidative esterification aldehydes. A and efficient protocol for transformation a wide range sterically hindered α‐ β‐substituted aliphatic aldehydes/enals, catalyzed by novel readily accessible N‐Mes‐/N‐2,4,6‐trichlorophenyl 1,2,4‐triazolium salt, acid co‐catalyst, was developed. whole series α/β‐substituted aldehydes/enals hitherto not amenable to...

Abstract The roles of nickel and chromium catalysts in the coupling reaction vinyl halides aldehydes, so‐called Nozaki–Hiyama–Kishi (NHK) reaction, have been studied by UV/Vis spectroscopy, electrochemical, spectroelectrochemical methods. Electrochemical studies revealed that plays central role activating halide reductive cleavage, to form a rapidly decomposing vinyl–Ni species. latter can, however, be stabilized presence Cr complex. redox behavior Ni complexes demonstrated activation...

An efficient oxidative NHC-catalyzed one-step transformation of (S)- or (R)-8-oxocitronellal to nepetalactone (NL) in enantio- and diastereomerically pure form has been developed. Several new "easy make" N-Mes- N-Dipp-substituted 1,2,4-triazolium salts carrying nitroaromatic groups on N1 were synthesized evaluated as precatalysts combination with base stoichiometric organic oxidant. Under optimized conditions, NLs are accessible very good yields under mild conditions. The oxidant used could...

Abstract We report the discovery that simple carboxylic acids, such as benzoic acid, boost activity of N‐heterocyclic carbene (NHC) catalysts in oxidative esterification aldehydes. A and efficient protocol for transformation a wide range sterically hindered α‐ β‐substituted aliphatic aldehydes/enals, catalyzed by novel readily accessible N‐Mes‐/N‐2,4,6‐trichlorophenyl 1,2,4‐triazolium salt, acid co‐catalyst, was developed. whole series α/β‐substituted aldehydes/enals hitherto not amenable to...

The vicinal dianion 2 derived from triethyl ethanetricarboxylate reacted regioselectively with aldehydes and ketones at C(β) to provide paraconic acid derivatives 5a–f in moderate high yields as mixtures of diastereoisomers. 5e 5f were utilized the starting materials for syntheses (±)-lichesterinic (12), (±)-phaseolinic (13), (±)-nephromopsinic (14), (±)-rocellaric (15), (±)-dihydroprotolichesterinic (16).

A highly efficient asymmetric synthesis of α,γ-substituted γ-amino sulfonates via diastereoselective ring-opening enantiopure γ-sultones with inversion configuration at the attacked γ-carbon is described. In key step sodium azide used as nucleophilic nitrogen source. Secondary and tertiary were synthesized in very good yields excellent diastereo- enantiomeric excesses (de, ee ≥98%).

The first auxiliary controlled synthesis of enantiopure α,γ-substituted γ-sultones via α-allylated chiral sulfonates is described. high asymmetric inductions the α-allylations were reached with our previously described 1,2:5,6-di-O-isopropylidene-α-d-allofuranose (de≥98%). Cleavage and successive diastereoselective ring closure sulfonic acid intermediates led to title compounds in selectivities (de, ee≥98%) good excellent yields (52-90%). Enantiopure are interesting reaction various nucleophiles.

A practical one-pot procedure for the preparation of Singh's catalyst from either l-/d-proline or Boc-proline is described. The coupling partner, a chiral amino alcohol, can be prepared and used directly without purification corresponding acid ester. Moreover, tert-butoxycarbonyl (Boc) group removal using concentrated HCl in MeOH–DCM was developed utilized multigram-scale synthesis catalyst.

The Prins reaction is an efficient method for the direct generation of 1,3-dioxanes from alkenes and aldehydes. As first published in 2008, this process can be effected by <i>stoichiometric</i> amounts molecular iodine. We herein report a <i>catalytic</i> protocol allowing use iodine at low loading (0.5–5 mol%), smoothly effecting condensation styrenes with aliphatic aldehydes to <i>rac</i>-1,3-dioxanes. Moreover, mild catalytic system effects isomerization 1,3-dioxane products...

Abstract The first auxiliary controlled asymmetric synthesis of enantiopure α,γ‐substituted γ‐sultones via α‐allylation lithiated sulfonates by using 1,2:5,6‐di‐ O ‐isopropylidene‐α‐ D ‐allofuranose as chiral is described. high inductions the α‐allylations were reached in good to excellent yields. Successive epimerization‐free cleavage and diastereoselective ring closure sulfonic acid intermediates a one‐pot procedure led title compounds yields diastereo‐ enantiomeric excesses ( de , ee ≥...

The diastereoselective Michael addition of lithiated enantiopure sulfonates to nitroalkenes is described. High asymmetric inductions were obtained by using 1,2:5,6-di-O-isopropylidene-α-d-allofuranose as a cheap and easily available chiral auxiliary. Racemization-free cleavage the auxiliary led α,β-disubstituted γ-nitro methyl sulfonates. A change conditions resulted in β-alkoxycarbonyl via Meyer reaction (de ≥ 98%, ee 98%).

Abstract We report an efficient and practical protocol for the Cr/Ni‐catalyzed vinylation of aldehydes, based on use Mn/Cr alloy (ca. 10 % Cr) TMSCl. No additional Cr salts need to be added. In presence NiCl 2 (0.3 mol %) a bis(ketimino)‐2,2′‐bipyridine as N 4 ‐chelating ligand (1 %), vinylations proceed smoothly at room temperature. The catalytic amounts MeOH LiOAc additives was found further promote efficiency system, even in absence ligand. Detailed reaction monitoring revealed that...

The hydrolysis of enantiopure α,γ-substituted γ-sultones with water under mild conditions leads to γ-hydroxy methyl sulfonates in very good yields and excellent diastereo- enantiomeric excesses (de, ee ≥ 98%). reaction proceeds via a SN2 mechanism inversion configuration at the attacked γ-carbon atom whose absolute was established by X-ray crystallography.

An efficient asymmetric synthesis of β-hydroxy ­sulfonates is described via stereocontrolled aldol reactions using 1,2:5,6-di-O-isopropylidene-α-d-allofuranose as the chiral auxiliary. The with aromatic aldehydes yielded predominantly syn adducts in very good yields and excellent diastereo- enantiomeric excesses (de, ee ≥98%).

Abstract Introduction The active compound ( E )‐1‐(3′,4′‐dimethoxyphenyl)butadiene (DMPBD) isolated from the rhizomes of Zingiber cassumunar Roxb. has potent anti‐inflammatory and anticancer activities. Although DMPBD is one promising drug candidates for phytomedicine, its limited stability impedes widespread use. For development new drugs, assessment their chemical essential, ensuring they maintain properties within specified limits throughout period production until Objective In present...

An efficient asymmetric synthesis of substituted β-alkoxycarbonyl sulfonates is described. Enantiopure α-substituted can be obtained via α-alkylation metalated bearing 1,2:5,6-di-O-isopropylidene-α-d-allofuranose as the chiral auxiliary with alkyl bromoacetates. α,β-Di­substituted were prepared starting from corresponding enantiopure γ-nitro by using TFA for cleavage and causing a simultaneous Meyer reaction.

Abstract Clinical translation of pluripotent stem cell (PSC) derivatives is hindered by the tumorigenic risk from residual undifferentiated cells. Here, we identified salicylic diamines as potent agents exhibiting toxicity to murine and human PSCs but not cardiomyocytes (CMs) derived them. Half maximal inhibitory concentrations (IC 50 ) small molecules SM2 SM6 were, respectively, 9- 18-fold higher for than PSCs, while IC SM8 was comparable both PSC groups. Treatment embryoid bodies in...

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Abstract For see ChemInform in Full Text.