Catalysis by heteropoly acids (HPAs) and related compounds is a field of growing importance, attracting increasing attention worldwide, in which many new and exciting developments are taking place in both research and technology [1–111, HPAs are polyoxometalates incorporating anions (heteropolyanions) having metal-oxygen octahedra as the basic structural units [ll-141. Among a wide variety of HPAs those belonging to the so-called Keggin series are the most importance for catalysis. They include heteropolyanions (HPANs)

Heteropoly Acids and Related Compounds as Catalysts for Fine Chemical Synthesis

How easy are the syntheses of allenes

As the chemistry of saccharides and related molecular species plays a significant role in the metabolic pathways of living organisms, detecting the presence and concentration of biologically important sugars in aqueous solution is necessary in a variety of medicinal and industrial contexts. The recognition of d-glucose is of particular interest, for example in the monitoring of diabetics. Recent research provides clear evidence that tight control of blood sugar levels in diabetics sharply reduces the risk of long term complications, which include blindness, kidney failure, heart attacks and even gangrene and amputation of the limbs. Current enzymatic detection methods of sugars offer specificity for only a few saccharides; additionally, enzyme based sensors are unstable in harsh conditions. Phenylboronic acid has been known for 120 years. However, it took until 1959 for the first quantitative evaluation of saccharide boronic acid interactions. Boronic acids react with 1,2 or 1,3 diols of saccharides to form five- or six-membered cyclic esters in non-aqueous or basic aqueous media. The stable boronic acid-based saccharide receptors offer the possibility of creating saccharide sensors ‘chemosensors’ which are selective and sensitive for any chosen saccharide.

Artificial Receptors as Chemosensors for Carbohydrates

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered.

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Electrochemically synthesized polymers in molecular imprinting for chemical sensing

As master craftsmen, modern synthetic chemists are challenged to achieve remarkable feats of efficiency and elegance toward molecular targets. The nature of this pursuit necessitates the collection of synthetic repertoires that are tried and true. With methodologies and pathways increasingly scrutinized, the adept chemist must seek out propitious tools to incorporate into the arsenal. With this in mind, this Account highlights the versatility of alkoxyallenes as precursors to valuable heterocyclic building blocks for such efforts as natural product synthesis. Accessed by the etherification of either propargyl alcohols or propargylic halides, alkoxyallenes are obtained after base-catalyzed isomerizations of the propargylic ethers. A host of umpolung synthons are available through this scheme after metalation, generating C3 nucleophiles synthetically equivalent to vital anionic and zwitterionic synthons. Reactions with a diverse set of heteroatomic electrophiles yield carbohydrates, spiroketals, alkaloids, ...

Sugars, Alkaloids, and Heteroaromatics: Exploring Heterocyclic Chemistry with Alkoxyallenes†

Enyne-hydrocarbons, -alcohols and -ethers with the system can be converted into the isomers with a terminal acetylenic group , by treating them with an excess of potassium amide in liquid ammonia and hydrolysing the reaction mixture thus formed. In most cases yields are excellent.



Enyne thioethers RCC-CHCH-SC2H5 (R alkyl) undergo an elimination of ethanethiol under these conditions. Hydrolysis affords the 1,3-diynes RCC-CCH in very good yields.

Chemistry of acetylenic ethers: 78 Isomerization of some conjugated enyne compounds

Bifunctional acetylenic ethers ROC≡C(CH2)nC≡COR can be prepared by alkylation of alkoxyethynyl-sodium or -lithium with α,ω-dihalides in liquid ammonia The compounds obtained, and other acetylenic ethers synthesized by alkylation of alkoxyethynes, are listed in table I



The bifunctional ether CH3C≡C·O·CH2CH2·O·C≡CC;H3 was prepared as outlined in the reaction scheme on page 520

Chemistry of acetylenic ethers LVII: Bifunctional acetylenic ethers

The amino-acid sequence of 2,4-dinitrophenyl-peptide methyl esters has been determined by mass spectral analysis. Using this technique, the structure of a number of simple peptides isolated from pig neurohypophysis, could be elucidated. The structure of valyl-leucine, alanyl-valyl-leucine, tyrosyl-glycine and O-Acetyl-tyrosyl-valine was established.

Structure determination of unknown peptides isolated from pig neurohypophysis, by mass spectrometrical analysis: (Of their 2,4-dinitrophenyl peptide methyl esters)

Chemistry of acetylenic ethers. LIII: Conversion of acetylenic ethers into α‐ketoesters

Treatment of the carbinols (CH3)2C=C=C=C(OCH3)CR1R2(OH) (I) with potassium tert-butoxide in dimethyl sulfoxide gives derivatives of furan (III) if R2 = H and derivatives of 2,5-dihydrofuran (II) if R1 and R2 are both alkyl or if R1R2C = cyclohexyl. Acid-catalysed hydrolysis of II and III affords derivatives of 3-oxo-2,3-dihydrofuran (IV).



Potassium amide in liquid ammonia, when used in excess, causes isomerisation of I into CH2=C(CH3)CH=C=C(OCH3)CR1R2(OH) (Ia).

J. F. Arens

Papers

Chemistry of acetylenic ethers: 78 Isomerization of some conjugated enyne compounds

Chemistry of acetylenic ethers LVII: Bifunctional acetylenic ethers

Structure determination of unknown peptides isolated from pig neurohypophysis, by mass spectrometrical analysis: (Of their 2,4-dinitrophenyl peptide methyl esters)

Chemistry of acetylenic ethers. LIII: Conversion of acetylenic ethers into α‐ketoesters

Derivatives of furan and 2,5-dihydrofuran from cumulenic carbinol ethers