The use of polymer-bound triphenylphosphine in the stereochemical inversion of secondary alcohols

Polymer-bound triphenylphosphine can replace triphenylphosphine in the Mitsunobu reaction to generate stereochemically inverted secondary alcohols. This method is comparable with the standard Mitsunobu reaction in terms of inversion of stereochemistry, yield, and reaction time, even for sterically very hindered secondary alcohols. The special merit of this reaction is that the excess polymer-bound triphenylphosphine and its by-products are easily removed by filtration from the reaction products.     

Organocatalytic Mitsunobu reactions

A catalytic Mitsunobu reaction system is described in which the azo reagent is used as an organocatalyst and iodosobenzene diacetate is used as the stoichiometric oxidant. In this system, iodosobenzene diacetate oxidizes the formed hydrazine byproduct to regenerate the azo reagent. Yields obtained in the catalytic reactions using a variety of carboxylic acids and alcohols were slightly lower than those obtained from corresponding stoichiometric reactions. Both primary and secondary alcohols can be used as substrates in this reaction system, with the secondary alcohols affording products with inverted stereochemistry at the carbinol center.     

Stereocontrolled synthesis of (-)-galanthamine

An enantioselective synthesis of (-)-galanthamine has been realized in 11 linear steps starting from isovanillin. A Mitsunobu aryl ether forming reaction was used to assemble the galanthamine backbone, which was stitched together using enyne ring-closing metathesis, Heck, and N-alkylation reactions affording the tetracyclic ring system. Control of relative and absolute stereochemistry was derived from an easily accessible enantiomerically enriched propargylic alcohol 13.     

Synthesis of Molecular Frameworks Containing Two Distinct Heterocycles Connected in a Single Molecule with Enhanced Three‐Dimensional Shape Diversity

Herein, we report the synthesis of fused‐triazole scaffolds that are connected by pyrimidines, pyrazoles, or pyrazolopyrimidines through carbohydrate‐derived stereodivergent linkers. Pyrimidine‐, pyrazole‐, or pyrazolopyrimidine‐based carbohybrids were constructed through condensations of the key intermediates, 2‐C‐formyl glycals, with various dinucleophiles. Fused‐triazole scaffolds were obtained through intramolecular 1,3‐dipolar cycloadditions after selective functionalization of the carbohybrid polyol moieties with azide and alkyne functionalities using S_N2‐type alkylations or Mitsunobu reactions. Overall, this synthetic method affords two distinct privileged substructures in a single molecule, connected by stereodivergent diol linkers derived from abundant natural chiral sources, namely, carbohydrates. The resulting vicinal diols in the linker were further modified to achieve unique connectivities between the two privileged structures for maximized three‐dimensional shape diversity, which we called the linker diversification strategy.     

Mercury(II) oxide/tetrafluoroboric acid-promoted vicinal hydroxy- and alkoxylation of alkenes

The reaction of alkenes with mercury(II) oxide/tetrafluoroboric acid and alcohols or water involves reduction to Hg(O) and vicinal diethers or diols are produced in good yields. Olefins bearing benzylic hydrogens in an α position lead to cinnamyl ethers. Mechanisms are proposed to account for the products and their stereochemistry.     

Glycol-cleavage reagents also act on stannylene derivatives.

The well-known cleavage reactions of vicinal diols by such reagents as Pb(OAc)₄, NaIO₄, PhI(OAc)₂ and Ph₃Bi^V-compounds have now been observed for the first time on covalent derivatives of these vicinal diols, their dibutylstannylenes.     

Investigations into the selective oxidation of vicinal diols to α-hydroxy ketones with the NaBrO3/NaHSO3 reagent: pH dependence, stoichiometry, substrates and origin of selectivity

The NaBrO₃/NaHSO₃ reagent is one of the few oxidizing agents that chemoselectively oxidizes vicinal diols to α-hydroxy ketones with little overoxidation to the corresponding vicinal-dione or dicarboxylic acid. Oxidation reactions performed with this reagent showed strong pH dependence. cis-Vicinal diols reacted faster than trans-vicinal diols to the α-hydroxy ketone product. Hydroxy functional groups at axial ring positions were more readily oxidized than equatorial hydroxy groups. The application of the NaBrO₃/NaHSO₃ reagent for the chemoselective oxidation of vicinal diols was limited to simple systems and failed with more complex monosaccharide compounds probably due to acid catalyzed dehydrogenation reactions. Despite the simple reaction set-up and good selectivity towards the α-hydroxy ketone product, the actual oxidation reaction mechanism is highly complex and postulated to involve at least six different equilibria with a plethora of bromine containing species. A possible oxidation reaction mechanism is discussed.     

Combined carbometalation-zinc homologation-allylation reactions as a new approach for alkoxyallylation of aldehydes

The combined carbometalation reaction of ynol ethers followed by a zinc homologation and further allylation reactions lead to an efficient preparation of allylic vicinal diols. The stereochemical outcome of the reaction shows that the substituent of the aldehyde occupies a pseudoaxial position in a Zimmerman-Traxler transition state.     

Asymmetric dihydroxylation of d-glucose derived alpha,beta-unsaturated ester: synthesis of azepane and nojirimycin analogues

The asymmetric dihydroxylation of a d-glucose derived alpha,beta-unsaturated ester 3 afforded syn vicinal diols in good to high diastereoselectivity. The conversion of these vicinal diols to the corresponding cyclic sulfate, regio-, stereoselective nucleophilic ring opening by sodium azide, and LAH reduction afforded amino heptitols 7a,b that were converted to azepane 1c,d and nojirimycin analogues 2c,d.     

Aspects of stereochemistry—I Properties and reactions of some diols

The extent of intramolecular hydrogen-bonding, as determined by infra-red spectroscopy in the hydroxyl stretching region, in certain vicinal diols of cyclohexane, cyclopentane, tetrahydropyran and tetrahydrofuran and in related compounds provides evidence for the stabilities of different conformations. In certain compounds these stabilities can be affected by hydrogen bonding from a substituent hydroxyl group to a ring oxygen. Additional evidence is provided in the case of the tetrahydropyran diols by [M]_D values. The rate of reaction of the vicinal diols of these cyclic systems with glycol splitting reagents, and their zone electrophoretic mobility in an alkaline borate buffer is influenced by the presence of a ring oxygen.     

Regioselective enzymatic acylation of vicinal diols of steroids

Monoacylated derivatives of a complete set of 2,3- and 3,4-vicinal diols of steroids were prepared by regioselective lipase-catalysed transesterification reactions. The enzymes displayed different selectivities towards the vicinal diols depending on the configuration of the hydroxyl groups.     

Thermodynamic favorable CO2 conversion via vicinal diols and propargylic alcohols: A metal-free catalytic method

Organocatalysis represents a promising field in chemical fixation of CO2.Herein,a facile metal-free strategy was reported for the one-pot preparation of cyclic carbonates and a-hydroxy ketones from vicinal diols,propargylic alcohols and CO2.Wide scope of vicinal diols and propargylic alcohols was demonstrated to be efficient under the DBU-catalyzed conditions.A plausible mechanism was proposed,which included detailed main and side reactions under the metal-free conditions.     

Kinetics and mechanism of the oxidation of some vicinal and non-vicinal diols by tetrabutylammonium tribromide

Kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers, by tetrabutylammonium tribromide (TBATB) has been studied. The vicinal diols yield products arising out of glycol-bond fission, while the non-vicinal diols produce the hydroxycarbonyl compounds. The reaction is first-order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to diols. The reaction fails to induce the polymerization of acrylonitrile. There is no effect of tetrabutylammonium chloride on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of any primary kinetic isotope effect. Values of solvent isotope effect, k(H₂O)/k(D₂O), at 288 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutan-1-ol are 3.41, 0.98 and 1.02 respectively. A mechanism involving a glycol-bond fission has been proposed for the oxidation of vicinal diols. Non-vicinal diols are oxidised by a hydride-transfer mechanism, as they are monohydric alcohols.     

绿色催化二氧化碳、炔丙醇和亲核试剂的三组分反应

近些年来,将CO₂转化为高附加值化学品受到广泛关注。其中,CO₂、炔丙醇和亲核试剂的三组分反应可用于制备用途广泛的羰基化合物,该方法具有步骤经济性、原子经济性等优点。由于CO₂分子具有热力学稳定性和动力学惰性,多数CO₂参与的化学反应在热力学上不支持。然而,CO₂、炔丙醇和双亲核试剂三组分反应是热力学有利的CO₂转化反应,实现了邻二醇或氨基醇和CO₂到环状碳酸酯以及2-噁唑啉酮的高效转化。本综述旨在于总结并讨论近年来CO₂、炔丙醇和亲核试剂三组分反应制备多种羰基化学物的主要进展。     

Grafting and initiation reactions

Grafting of acrylic monomers onto cellulose substrates in acid aqueous medium using complex of Mn³⁺ ions as a redox initiator is described. Assuming that the /Mn³⁺/ ions react with aldehydes and vicinal diols, the rate of these reactions has been measured spectroscopically. (ESR and visible light) using model compounds. It is concluded that the /Mn³⁺/ grafting onto cellulose is a radical reaction initiated mainly by oxidation of aldehydes at reducing end groups and C-C bond scission of vicinal diols at the end groups and along the cellulose chains. The initiation rates of the Ce⁴⁺, /Mn³⁺/ and VO₂²⁺ redox ions are related to their oxidation potential.     

Kinetics and mechanism of the oxidation of some diols by benzyltrimethylammoniumtribromide

The kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers by benzyltrimethylammonium tribromide (BTMAB) have been studied in 3:7 (v/v) acetic acid-water mixture. The vicinal diols yield the carbonyl compounds arising out of the glycol bond fission while the other diols give the hydroxycarbonyl compounds. The reaction is first-order with respect to BTMAB. Michaelis-Menten type kinetics is observed with respect to diol. Addition of benzyltrimethylammonium chloride does not affect the rate. Tribromide ion is postulated to be the reactive oxidizing species. Oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of a kinetic isotope effect. The reaction exhibits substantial solvent isotope effect. A mechanism involving a glycol-bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidized by a hydride ion transfer to the oxidant, as are the monohydric alcohols.     

Synthetic studies on chartelline C: stereoselective construction of the core skeleton

What a core-ker! The title synthesis was achieved using a route featuring an intramolecular Mitsunobu reaction of a nosyl amide, stereoselective construction of the β-lactam, and formation of an enamide moiety by selenoxide elimination. The stereochemistry of the alkylation for the formation of the β-lactam was controlled by a secondary hydroxy group on the ten-membered ring. SEM=2-(trimethylsilyl)ethoxymethyl; TBS=tert-butyldimethylsilyl.     

Antiradical activity of dioxolane derivatives

1,3-Benzodioxoles synthesized by condensation of 3,6-di-tert-butylbenzene-1,2-diol with carbonyl compounds showed antiradical activity due to their ability to undergo one-electron oxidation with formation of stable radical cations. On this basis, the antiknock effect of their structural analogs, 1,3-dioxolanes derived from vicinal diols, was interpreted in terms of oxidation of these compounds with active radicals generated from fuel hydrocarbons to produce more stable radical or radical ion species, depending on the fuel composition. The formation of radical species was detected in model oxidation reactions of 2,2-dimethyl-1,3-dioxolane and 2,2-dimethyl-1,3-dioxolan-4-ylmethanol with radicals generated by photolysis of iron(III) chloride and benzoyl peroxide.     

A more convenient and general procedure for O-monobenzylation of diols via stannylenes: a critical reevaluation of the Bu2SnO method

A more consistent, straightforward, and economical protocol for generation of stannylene species and their reaction with BnBr leading to products of O-monobenzylation of diols has been set. It has shown to be specially indicated for substrates bearing vicinal trans 1,2-diol moieties on cyclohexane backbones, which are more resistant to these transformations. Such protocol has been successfully applied to myo-inositol derivatives and acyclic diols.     

Asymmetric reduction of α-hydroxy aromatic ketones to chiral aryl vicinal diols using carrot enzymes system

Asymmetric reduction ofα-hydroxy aromatic ketones was carried out by using carrot enzymes system,yielding corresponding chiral vicinal diols with special functional groups.The optimum reaction conditions were obtained after investigation of various influencing factors.Chiral aryl vicinal diols were produced with good yields and excellent enantiomeric excesses under appropriate conditions.Meanwhile,the steric factors and electronic effects of the substituents on the aromatic ring were shown to have an interesting influence on both yield and enantioselectivity.