Conversions of Allyl Ethers in a Superbasic Medium

Conversions of alkyl allyl and terpenoid allyl ethers in a superbasic medium (dimethyl sulfoxidepotassium hydroxide) are studied. The ethers with an unbranched alkyl substituent isomerize into propenyl ethers, the ethers with a branched unsaturated substituent decompose to give a hydrocarbon, and diallyl ethers isomerize into allyl vinyl ethers whose Claisen rearrangement gives rise to aldehydes.     

Twenty-five Years of "Crowning" Around: Synthesis of Crown Ethers at Brigham Young University

A review of the synthesis of crown ethers at Brigham Young University ispresented. Topics include: thiacrown ethers, diestercrown ethers,proton-ionizable crown ethers, chiral crown ethers, azacrown ethers,cryptands and other polycyclic ligands, and the Mannich reaction method toprepare azacrown ethers and cryptands.     

New methodology for the synthesis of benzoazacrown ethers by transformation of the macrocycle of benzocrown ethers

The review summarizes the results of studies aimed at constructing new promising macrocyclic ligands that bind metal and ammonium ions. A new approach to the synthesis of formyl and nitro derivatives of 1-aza-2,3-benzocrown ethers possessing considerable synthetic potential is described. The review presents a radically new methodology for the synthesis of such benzoazacrown ethers based on stepwise transformations of the macrocycle of readily accessible benzocrown ethers. The main structural factors and necessary conditions enabling stepwise transformations of the macrocycle of crown ethers into azacrown ethers were revealed. For the first time, the ability of N-methylbenzoazacrown ethers to form complexes was found, which is much superior to that of widely used N-phenylazacrown ethers and benzocrown ethers with the same size of the macrocycle.     

Komplexierungseigenschaften von Pyridinokronenethern gegenüber Alkali- und Erdalkaliionen in Methanol

Complexing Properties of Pyridino Crown Ether with Alkali and Alkali-Earth Cations in Methanol The stability constants and thermodynamic values of the complex formation of several pyridino crown ethers with alkali and alkaline-earth cations were determined by calorimetric titration in methanol. The stability of the complexes is lower than with crown ethers. This is mainly caused by a decrease of reaction enthalpies. Compared with other mono substituted crown ethers the complexes with pyridino crown ethers are fare more stable due to entropic effects. With increasing cavity size the stability constants, enthalpies and entropies for the reaction of crown ethers and pyridino crown ethers approach similar values.     

A catalytic amount of nickel(II) chloride hexahydrate and 1,2-ethanedithiol is a good combination for the cleavage of tetrahydropyranyl (THP) and tert-butyldimethylsilyl (TBS) ethers

Various THP and TBS ethers can be unmasked easily to the corresponding hydroxyl compounds in good yields by using a combination of a catalytic amount of nickel(II) chloride hexahydrate and 1,2-ethanedithiol at room temperature. In addition, alkyl TBS ethers can be hydrolyzed chemoselectively in the presence of aryl TBS ethers. Moreover, alkyl TBS ethers can be cleaved easily in the presence of alkyl or aryl THP ethers using the same conditions.     

DIRECT CONVERSION OF SILYL ETHERS OR TETRAHYDROPYRANYL ETHERS INTO THE CORRESPONDING DIPHENYLMETHYL ETHERS

Direct conversion of alcohol silyl ethers into the corresponding diphenylmethyl (DPM) ethers can be easily performed by the reaction with diphenylmethyl formate in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate. By the additional use of triethylsilane, tetrahydropyranyl ethers can be also converted into the corresponding DPM ethers.     

Spectrometrie de masse,problemes de structure et de stereochimie—CCVII Fragmentations des Ethers Insatures

In connection with work on computerized mass spectral interpretation of organic com-pounds, the behavior of three groups of unsaturated ethers was examined: allylic, substituted allylic and unsaturated ethers with 2 or 3 methylene groups between the oxygen atom and the double bond. A total of 36 compounds (11 labelled) were prepared and mechanistic rationalizations presented. The allylic ethers isomerized to vinylic ethers after ionization. No double bond migration was observed, however, before or after electron-impact of allylic and homoallylic ethers or ethers with 3 methylene groups between the oxygen atom and the double bond. The allylic ethers with seven carbon atoms in the saturated chain lost a saturated alcohol molecule [R' + C₃H₆OH] by a uni-directional quadruple hydrogen transfer prior to fragmentation.     

Collision-activated dissociation mass spectra of crown ethers,perfluorinated crown ethers and related macrocycles

The collision-activated dissociation (CAD) mass spectra for a series of crown ethers, perfluoro crown ethers, cryptands and several dicyclohexano substituted crown ethers are reported. The CAD spectra were acquired with a triple quadrupole mass spectrometer, and in some cases spectra were recorded as a function of collision energy. In general, the protonated crown ethers dissociate via a series of losses of C₂H₄O units. The perfluoro crown ethers dissociate predominantly via losses of C₂F₄O units. The dicyclohexano ethers fragment in analogous ways in conjunction with cleavage of the cyclohexano rings. CAD spectra are also reported for acyclic ether systems.     

Selective Deprotection of tert -Butyldimethylsilyl Ethers Using Nafion-H®/Sodium Iodide (or Bromodimethylsulfonium Bromide) in Methanol

Abstract

Catalytic amounts of bromodimethyl sulfonium bromide, or Nafion-H along with NaI (1 equiv.), in methanol cleave a variety of TBDMS ethers readily in high yields. Alkyl TBDMS ethers react more readily and selectively compared to phenolic TBDMS ethers, benzyl, and methyl ethers.     

A study on the reductive fission of β-aromatic imino ethers

Reduction of ethers containing various imino systems with sodium in boiling ethanol was shown to give different results, thus, β-aryl substituted imino ethers can be reduced and cleaved, while β-aliphatic imino ethers are not susceptible to sodium-alcohol reductive fission. In the synthesis of β-imino ethers it has been found that molecular sieve is a good condensation catalyst for the formation of highly hindered Schiff bases.     

Synthesis of Polycyclic Ethers by Two-Directional Double Ring-Closing Metathesis

trans-Fused tricyclic ethers containing combinations of six-, seven-, eight-, and nine-membered rings are constructed using two-directional double ring-closing metathesis reactions (see scheme). Such double cyclizations of precursors bearing alkenes, allylic ethers, enol ethers, or alkynyl ethers offer a new strategy for the synthesis of brevetoxins and ciguatoxins. PMB=(p-MeOC(6)H(4)CH(2)).     

The synthesis of unique structures of tetra-crown ethers through Michael addition

Unique structures of tetra-crown ethers were successfully synthesized by the reaction of tetramethylolmethane tetraacrylate (TMMT) reacted with crown ethers containing primary amine functional group such as 2-aminomethyl crown ethers and 4-aminobenzo crown ethers; containing secondary amine group like 1-aza crown ethers through Michael reaction. The newly synthesized tetra-crown ethers were characterized by ¹H NMR, ¹³C NMR, FAB mass spectrum, elemental analyses, IR, respectively.     

Cationic polymerization of α,β-disubstituted olefins. V. Reactivity of propenyl alkyl ethers in cationic polymerization

To elucidate the effect of the introduction of a methyl group in the β-position of a vinyl monomer, propenyl alkyl ethers were copolymerized with vinyl ethers having the same alkoxy group. Propenyl alkyl ethers with an unbranched alkoxy group (ethyl or n-butyl propenyl ether) were more reactive than the corresponding vinyl ethers. This behavior is quite different from that of β-methylstyrene derivatives. However, propenyl alkyl ethers with branched alkoxy groups at the α carbon atom (isopropyl or tert-butyl propenyl ether) were less reactive than the corresponding vinyl ethers. Also, cis- isomers were more reactive than the trans isomers, regardless of the kind of alkoxy group and the polarity of the solvent.     

Influence of allyl ethers on free radical polymerization of styrene

The effect of allyl ethers on the free radical polymerization of styrene has been studied with respect to chain transfer, copolymerization, and conversion. The studies have been performed in an inert atmosphere or in air. Six different allyl ethers have been used as model substances in order to show the effect of structural differences of the ethers on the polymerization. Contrary to what was expected, no chain transfer through hydrogen abstraction was found. Nor did any copolymerization occur. When the polymerization was performed in air, the allyl ethers had a retarding effect on the polymerization rate, due to oxidation of the allyl ethers. The oxidation rate of the allyl ethers was found to be related to their structure, where the functionality and presence of intramolecular hydrogen bonding are the main factors.     

Gas-liquid chromatography-mass spectrometry of acetates of partially methylated methyl glycosides. VII. Mono- and dimethylheptoses

The partial methylation of methyl β-glucoheptopyranoside has given a complex mixture of methyl ethers, from which five monomethyl ethers have been isolated by preparative GLC. Methylation of the latter gave a mixture in which ten dimethyl ethers were detected. The retention indices on the phase NPGS of the mono- and dimethyl ethers of methyl β-glucoheptopyranoside have been measured, and their mass spectra have been recorded and discussed. The mass spectra of these position isomers unambiguously characterize the pattern of methylation.     

Methods for the interconversion of protective groups. Transformation of mem ethers into isopropylthiomethyl ethers or cyanomethyl ethers

This letter describes methods for the synthesis of isopropylthiomethyl and cyanomethyl ethers from the corresponding MEM ethers and also a process for the cleavage of MEM or MOM ethers of 1,2- and 1,3-diols which avoids cyclization to formals.     

Isomerization of allyl ethers initiated by lithium diisopropylamide

Lithium diisopropylamide (LDA) promotes virtually quantitative conversion of allylic ethers to (Z)-propenyl ethers. It was discovered that allylic ethers can be isomerized efficiently with very high stereoselectivity to (Z)-propenyl ethers by LDA in THF at room temperature. The reaction time for the conversion increases with more sterically hindered allylic ethers. Different amides were also compared with LDA for their ability to effect this isomerization.     

Improved procedure for the reductive acetylation of acyclic esters and a new synthesis of ethers

An optimized protocol for the DIBALH reductive acetylation of acyclic esters and diesters is described. This reductive acetylation procedure allows a wide variety of esters to be converted into the corresponding alpha-acetoxy ethers in good to excellent yields. It was found that, under mild acidic conditions, many alpha-acetoxy ethers can be further reduced to the corresponding ethers. This net two-step ester deoxygenation is an attractive alternative to the classical Williamson synthesis for certain ethers.     

Direct oxidative C(sp3) -H cyanation of secondary benzylic ethers

A practical and efficient oxidative CH cyanation of secondary benzylic ethers with TMSCN in the presence of DDQ is described for the first time. The metal-free process is well tolerated with a wide variety of electronically varied α-monosubstituted isochromans for the synthesis of isochromans bearing α-aryl α-cyano substituent patterns.     

Trinitroethyl ethers of substituted alcohols

The influence of the trinitromethane salt cations and the substituents in the alkyl moiety of chloromethyl ethers of alcohols on the yields of trinitroethyl ethers of the substituted alcohols formed from them was established. On this basis a representative series of previously unavailable trinitroethanol ethers was synthesized.