Stereoselective synthesis of methyl monate C

[Structure: see text] The stereoselective synthesis of methyl monate C 2 is described using as a key step an ene-intramolecular modified Sakurai cyclization (IMSC) reaction to prepare tetrahydropyran 5. An asymmetric allylic alkylation, followed by a cross-metathesis, enables the insertion of the right-hand side chain.     

凹凸棒石负载Cu-Fe-Co基催化剂组合体系用于CO加氢制备低碳醇

采用浸渍法(IM)和浸渍燃烧法(IMSC)制备了凹凸棒石(ATP)及凹凸棒石-多孔硅胶微球混合物(ATPS)负载CuFe-Co基改性费托催化剂,通过N_2吸附-脱附、X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、透射电镜(TEM)、H_2-程序升温还原(H_2-TPR)和CO_2-程序升温脱附(CO_2-TPD)等手段对催化剂进行了表征,并将它们应用于CO加氢制备低碳醇反应。结果表明,IMSC较IM制备催化剂更有利于CuO的负载、分散和还原,促进H_2和CO与Cu活性位的接触,但两者的最佳低碳醇合成温度均为280℃。通过对ATP和ATPS负载Cu-Fe-Co基催化剂(CFCK/ATP、CFCK/ATPS)与Cu/ZnO/Al_2O_3(CZA)甲醇催化剂的组合体系的优化,获得较理想的低碳醇合成催化剂组合体系CZA║CFCK/ATPS-IMSC。利用它们之间的"产物转化耦合效应",实现CO转化率为46.3%,低碳醇选择性为39.6%,C_(2+)醇含量为22.7%。     

An α-diaminoboryl carbanion assisted stereoselective single-pot preparation of α,β-disubstituted acrylonitriles

An α-diaminoboryl carbanion-mediated one-pot olefination directly converts an acetonitrile or the homologous nitrile into a series of α,β-disubstituted acrylonitriles in a stereoselective manner. The protocol involves the formation of an α-substituted α-diaminoboryl acetonitrile and subsequent olefination with an aldehyde. The use of an aryl or conjugated aldehyde preferentially leads to a (Z)-acrylonitrile, while an aliphatic aldehyde gave an (E)-isomer as a major product. Two complementary approaches, a linear method and a divergent method, are developed.     

Chiral Amine Catalyzed Reductive Aldol/Reductive Michael Addition Cascade Towards Enantioselective Synthesis of Benzannulated Diquinanes

Disclosed here an amine-catalyzed reductive aldol-condensation followed by an intramolecular reductive Michael-addition cascade employing Hantzsch ester as hydride source to a keto-bis-enone to provide enantio- and diastereoselective benzannulated diquinanes having three consecutive stereocenters, one of which is an all-carbon quaternary formyl stereocenter. Interestingly, on changing a tether connecting the ketone and an enone moiety from an aliphatic to an aromatic, a change in reactivity is observed. In this case, instead of the above-mentioned reductive aldol condensation, an asymmetric aldol reaction occurs, followed by an iminium/enamine isomerization and, finally diastereoselective Michael addition reaction occurs. As a result, a bis-benzannulated diquinane is obtained with vicinal congested quaternary chiral centers.     

Macrolactonization via Ti(IV)-mediated epoxy-acid coupling: a total synthesis of (-)-dactylolide [and zampanolide

A total synthesis of dactylolide (1) is described. The key feature involves the Ti(IV)-mediated coupling of structurally complex "Sharpless epoxides" and carboxylic acids in either an intramolecular (macrolactonization) or an intermolecular mode. Other notable aspects include a proton-catalyzed, cis-selective construction of the 4-methylenetetrahydropyran ring; a selective oxidation of an allylic alcohol in the presence of a 1,2-diol by an oxoammonium ion; an efficient ring-closing metathesis reaction of an in situ (bis-TMS) protected alpha,omega-diene-vic-diol; and an aluminum-mediated aza-aldol reaction of a primary amide to 1 to construct the acyclic carbinolamide in zampanolide.     

One-pot preparation of azobenzenes from nitrobenzenes by the combination of an indium-catalyzed reductive coupling and a subsequent oxidation

We demonstrated how a reduction step with a reducing system comprised of In(OTf)₃ and Et₃SiH and a subsequent oxidation that occurred under an ambient (oxygen) atmosphere allowed the highly selective and catalytic conversion of aromatic nitro compounds into symmetrical or unsymmetrical azobenzene derivatives. This catalytic system displayed a tolerance for the functional groups on a benzene ring: an alkyl group, a halogen, an acetyl group, an ester, a nitrile group, an acetyl group, an ester moiety, and a sulfonamide group.     

Nickeladihydrofuran. Key intermediate for nickel-catalyzed reaction of alkyne and aldehyde

The formation of a nickeladihydrofuran by oxidative cyclization of an alkyne and an aldehyde with nickel(0) has been demonstrated; the transformation of the nickeladihydrofuran into an enone by decomposition, a lactone by carbonylation and an allylic alcohol by treatment with ZnMe(2) suggests that nickeladihydrofuran is an important key intermediate in a variety of catalytic reactions.     

Geometry-selective synthesis of E or Z N-vinyl ureas (N-carbamoyl enamines)

N-Vinyl ureas are emerging as a valuable class of compounds with both nucleophilic and electrophilic reactivity. They may be made by capturing the enamine tautomer of an imine with an isocyanate, a reaction which in general leads to the E isomer of the vinyl urea. Deprotonation of such a vinyl urea, or of an allyl urea, generates a dipole stabilized Z-allyl anion which may be protonated to return the Z-vinyl urea. Isomerization of an allyl urea with a Ru complex provides an alternative route to E-vinyl ureas.     

Prevention of evaporation of small-volume sample solutions for capillary electrophoresis using a mineral-oil overlay.

The suppression of evaporation of water from small volumes of sample solutions or reagents for capillary electrophoresis by the use of a mineral-oil overlay was investigated in affinophoresis applications, in which the affinity constant of a mutant protein of recombinant human galectin-1 to a lactose affinophore, a triply negative charged ion having a lactoside as an affinity ligand, was determined. When an injection was carried out from a minimum of 20 microL of an aqueous solution beneath the oil overlay, no oil contamination inside the capillary was observed, provided the capillary was cleanly cut so that the end was flat, and the polyimide coating had been removed for a distance of about 2 mm from the end. Affinophoresis was carried out using 20 microL of an affinophore solution covered with an oil overlay. The abnormalities in the electropherograms as the result of the evaporation of the water from the solution during storage prior to use in an automatic operation of a capillary electrophoresis instrument were suppressed, with respect to the formation of a base line gap, an increase in the detection time of a marker ion and an increase in the initial current. A solution in a vial could be used repeatedly for a longer period of time when overlaid with mineral oil than in the absence of an overlay. The use of a mineral-oil overlay is a simple but very efficient technique for solving the problem of the evaporation of water from small volumes of aqueous solutions for use in capillary electrophoresis.     

Devices for Assisting Human Olfaction: Some Fundamental Experiments

Olfactory assist systems that allow the user to sense smells with amplified sensitivities are reported. We have developed two types of systems. The first system, an olfaction augmenter, detects the presence of a volatile organic compound in the air using a gas sensor, and presents an odor with an amplified intensity to the user using an odor generator. The second system, an olfactory concentrator, collects odor molecules in the air using an adsorbent, and presents the concentrated odor to the user. Results of our initial experiments on a prototype concentrator are reported.     

Manipulating replication processes within a dynamic covalent framework

The reaction of an amine bearing an amidopyridine recognition site and an aldehyde bearing a carboxylic acid recognition site affords an imine that is capable of directing its own formation through a dynamic covalent replication cycle. Additionally, the amine, formed by reduction of the replicating imine, is a more efficient catalyst for the formation of the replicating imine than the imine is a catalyst for its own formation.     

Copper(I) catalyzed regioselective asymmetric alkoxyamination of aryl enamide derivatives

The copper(I) catalyzed reaction of an enamide with an iminoiodane, in the presence of an alcohol, triggers the direct alkoxyamination of the double bond. This transformation represents a straightforward access to α-amino aminals in a completely regio- and diastereoselective manner. Use of a chiral Box ligand allows this reaction to be carried out in an enantioselective fashion.     

Synthesis of block copolymer containing dextran and polyamide sequences

A novel AB-type block copolymer composed of dextran and polyamide sequences was prepared through the following two approaches. One is a coupling reaction of a terminal functional group introduced in the dextran chain with that in the polyamide chain, such as the reaction of an amine group with an acyllactam group or that of a lactone group with an amine group at the corresponding chain ends. The other is an anionic polymerization of a bicyclic lactam activated with a trimethylsilylated dextran derivative having an acyllactam end group. The latter procedure was found to be more effective for the preparation of the block copolymer having a high molecular weight polyamide sequence.     

Regioselective allylzincation of alkenylboronate

[reaction: see text] Boryl substitution on an olefin activates the olefinic double bond toward addition of an organozinc reagent. Addition of an allylic zinc reagent to an alkenylboronate thus takes place smoothly to afford a variety of gem-zincio/boryl species. Theoretical studies with density functional calculations on the reaction pathway revealed that the reaction proceeds via a zincio-ene reaction rather than a bora-Claisen rearrangement.     

Electrodialysis in a non-aqueous medium: A clean process for the production of acetoacetic ester

Alkoxide is used as an agent and consumed in condensation reactions, e.g., in the production of acetoacetic ester. Working in an alcoholic medium and starting from a salt, it is possible to produce an alkoxide by means of electrodalysis. This principle was applied successfully for the production of acetoacetic ester and the recovery of the alkoxide in a single step. Such a process would offer self-sufficiency; the alkoxide could be recovered, thus foregoing the use of mineral acids and the consequent production of a salt as a waste. The merits can be seen in an economical as well as in an ecological context.     

Curtius rearrangement of aromatic carboxylic acids to access protected anilines and aromatic ureas

The reaction of a chloroformate or di-tert-butyl dicarbonate and sodium azide with an aromatic carboxylic acid produces the corresponding acyl azide, presumably through the formation of an azidoformate. The acyl azide undergoes a Curtius rearrangement to form an isocyanate derivative which is trapped either by an alkoxide or by an amine to form the aromatic carbamate or urea. The reaction conditions are compatible with a variety of functional groups and allow the synthesis of a number of aniline derivatives containing alkyl, halide, nitro, ketone, ether, and thioether substituents. [reaction: see text]     

Exploring the chemistry of epoxy amides for the synthesis of the 2'-epi-diazepanone core of liposidomycins and caprazamycins

New synthetic strategies have been explored for the synthesis of the structural core of liposidomycins and caprazamycins, an intriguing class of complex nucleoside-type antibiotics. This structural core is comprised of a cyclic diazepanone system linked to an uridyl fragment. The various synthetic approaches have in common that they originate from an epoxy amide derived from uridine, obtained via reaction of uridyl aldehyde 19 with an amide-stabilized sulfur ylide. Two different strategies were shown to be efficient in constructing the diazepanone ring system: (a) a reductive amination of an epoxy aldehyde with N-methylamine with subsequent intramolecular oxirane ring opening and (b) a carbene insertion reaction of an acyclic diazoamine precursor.     

De novo asymmetric synthesis of D- and L-swainsonine

[reaction: see text] The enantioselective syntheses of both enantiomers of the indolizidine natural product swainsonine have been achieved in 13 steps from furan. The indolizidine ring system is installed by a one-pot hydrogenolysis of both an azide and an O-Bn group along with an intramolecular reductive amination reaction. The asymmetry of swainsonine was introduced by Noyori reduction of an acylfuran. This route relies upon an Achmatowicz rearrangement, a diastereoselective palladium-catalyzed glycosylation, Luche reduction, and a dihydroxylation reaction.     

Total synthesis of (-)-anisatin

A novel synthetic route to (-)-anisatin has been developed. Our synthesis features a rhodium-catalyzed 1,4-addition of an arylboronic acid, an intramolecular Diels-Alder reaction of an ortho-quinone monoketal, a stereoselective [2,3]-Wittig rearrangement, and construction of the oxabicyclo [3.3.1] skeleton via cleavage of an epoxide by a primary amide.     

Anodic cyclization reactions: capitalizing on an intramolecular electron transfer to trigger the synthesis of a key tetrahydropyran building block

An anodic cyclization reaction between an enol ether radical cation and an oxygen nucleophile has been used to make a tetrahydropyran building block for the C(10)-C(16) portion of bryostatin. The oxidative cyclization was successful despite the presence of a thioacetal group that has a lower oxidation potential than the enol ether. Experimental evidence suggested that the reaction proceeded through an initial oxidation of the thioacetal followed by an intramolecular electron transfer to form the enol ether radical cation that was subsequently trapped by the oxygen nucleophile. The formation of the desired cyclic product could be explained using the Curtin-Hammett principle. By taking advantage of the intramolecular electron-transfer reaction, we used the presence of a thioacetal in an electrolysis substrate to selectively oxidize a proximal enol ether in the presence of an otherwise identical but more remote enol ether.