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.     

Enantioselective Claisen rearrangements with a hydrogen-bond donor catalyst

N,N'-Diphenylguanidinium ion associated with the noncoordinating BArF counterion is shown to be an effective catalyst for the [3,3]-sigmatropic rearrangement of a variety of substituted allyl vinyl ethers. Highly enantioselective catalytic Claisen rearrangements of ester-substituted allyl vinyl ethers are then documented using a new C2-symmetric guanidinium ion derivative.     

Derivatisation of steroid hormones with t-butyldimethylsilyl imidazole

An efficient procedure for the derivatisation of hydroxyl and alpha,beta-unsaturated ketonic steroids using t-butyldimethylsilyl imidazole is described. The conditions which employ potassium acetate as a basic catalyst result in quantitative formation of BDMS ethers and greater than 96% yield of BDMS-enol ethers. Various mechanisms involving the catalysed and uncatalysed reactions of t-butyldimethylsilyl imidazole with alcohols and enols are also discussed. The mass spectra of the BDMS-enol ethers, in contrast to the BDMS ethers, are dominated by an intense molecular ion, which facilitates the quantitation of these derivatives in biological samples. An example of the method is shown by the determination of 4-androstene-3,17-dione in urine using a stable-isotope internal standard.     

Regioselectivity in aromatic Claisen rearrangements

Theoretical calculations and the isomeric product composition for a series of eight meta-substituted allyl aryl ethers confirm the reliability of a new (1)H NMR methodology used to predict aromatic Claisen regioselectivity from ground-state conformational preference of the reactant allyloxy group. Frontier HOMO-LUMO intramolecular orbital interactions, a classical approach in predicting reactivity and selectivity for Claisen rearrangements of allyl vinyl ethers, is shown to fail to mimic transition-state orbital interactions for aromatic Claisen rearrangements of meta-substituted allyl aryl ethers. B3LYP/6-31G(d,p) calculations on reactants and transition states are shown, however, to correctly predict the outcome of such aromatic Claisen rearrangements from either the preferential reactant ground-state conformation (theoretical predictions that agree with the NMR measurements) or the less energetic transition state, or both.     

The ring-closing metathesis of vinyl ethers with Grubbs'' catalyst for the synthesis of dihydropyrans

A series of acyclic vinyl ethers have been prepared and treated with Grubbs' ruthenium catalyst ((Cy₃P)₂RuCl₂=CHPh). Contrary to previous findings, it has been shown that certain vinyl ethers are excellent substrates for the ring closing metathesis with ruthenium based catalysts.     

An efficient intermolecular BINAM-copper(I) catalyzed Ullmann-type coupling of aryl iodides/bromides with aliphatic alcohols

A wide range of alkyl aryl ethers are synthesized from the corresponding aryl iodides and aliphatic alcohols through Ullmann-type intermolecular coupling reactions in the presence of a catalytic amount of easily available BINAM-CuI complex. Less reactive aryl bromides have also been shown to react with aliphatic alcohols under identical reaction conditions to give good yields of the alkyl aryl ethers without increasing the reaction temperature and time.     

The mass spectra of some cyclic ethers

The mass spectral fragmentations of the saturated five-, six- and seven-membered ring ethers have been determined by studying their site-specifically deuterated analogues by both high and low-resolution mass spectrometry. The initial processes, governing the fragmentations of the cyclic ethers are shown to be identical with the well-known processes of linear nonbranched ethers, i.e. predominant α-fisson in the lower members and predominant carbon-oxygen fisson with charge retention on the carbon atom in the higher members.     

Dicobalt octacarbonyl-catalyzed cationic polymerization of allylic and enolic ethers

In the presence of silanes bearing Si H groups, dicobalt octacarbonyl [Co₂(CO)₈] efficiently catalyzes the cationic polymerization of a wide variety of enol ether and other related monomers including vinyl ethers, 1-propenyl ethers, 1-butenyl ethers, 2,3-dihydrofuran, 3,4-dihydro-2H-pyran, ketene acetals, and allene ethers. In addition, this catalyst system is also effective for the polymerization of complimentary allylic and propargylic ethers by a process involving tandem isomerization and cationic polymerization. This latter process occurs by a stepwise mechanism in which the allylic or propargylic ether is first isomerized, respectively, to the corresponding enol ether or allenic ether and then this latter compound is rapidly cationically polymerized in the presence of the catalyst. In accord with this mechanism, it has been shown that the structure of the polymers prepared from related enol and allyl ethers using the above catalyst system are identical. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1579–1591, 1997     

An efficient BINAM-copper(II) catalyzed Ullmann-type synthesis of diaryl ethers

A wide range of diaryl ethers are synthesized from the corresponding aryl iodides and phenols through Ullmann type coupling reactions in the presence of a catalytic amount of easily available BINAM-Cu(OTf)₂ complex under mild reaction conditions. Less reactive aryl bromides have also been shown to react with phenols under identical reaction conditions to give good yields of the diaryl ethers without increasing the reaction temperature and time.     

Palladium‐Catalyzed Regio‐ and Stereoselective Cross‐Addition of Terminal Alkynes to Ynol Ethers and Synthesis of 1,4‐Enyn‐3‐ones

Conjugated enynes, enol ethers, and enynones are versatile building blocks that can be elaborated by a wide variety of synthetic transformations. The selective synthesis of such units is a prerequisite for their effective utilization. The synthesis of conjugated 2‐phenoxyenynes through a palladium‐catalyzed cross‐addition of terminal alkynes to phenylethynyl ethers (hydroalkynylation) is now presented. The reaction is highly regio‐, stereo‐, and chemoselective, and shows excellent tolerance toward functional groups. The addition further features very mild reaction conditions (room temperature) and an inexpensive catalytic system (without a ligand and with a cheaply available Pd catalyst). The thus synthesized enynyl ethers with allylic hydroxy tethers, which survived the reaction, were shown to be ready precursors for valuable 1‐en‐4‐yn‐3‐ones.     

Allylsilyl Propargyl Ethers as Substrates for Intramolecular Pauson–Khand Reactions

Silyl ethers that are synthesized by coupling a propargylic alcohol with an allylsilyl chloride are shown to undergo sulfide‐promoted Pauson–Khand reactions, affording bicyclic enones.     

Identification of the products of nonregioselective organic reactions by chromatography-mass spectrometry: Chloro derivatives of dialkyl ethers

The possibilities of GC-MS identification of the products of free-radical chlorination of dialkyl ethers are considered. The principal feature of this problem was the absence of appropriate reference information (both mass spectra and GC retention indices) for chloro derivatives of ethers. It was shown that all monochloro and selected dichloro derivatives can be identified on the basis of joint interpretation of their mass spectra combined with evaluating the retention indices using different additive schemes.     

Komplexe zwischen Neutralmolekülen: Neutralkomplexe von krakenmolekülen mit kronenethern und anderen organischen molekülen

Crown ethers, water and several other neutral molecules are shown to form crystalline, strictly stoichiometric addition compounds with hexasubstituted benzene derivatives. These are suited for systematic investigations of intra- and intermolecular complexation between organic molecules.     

Templated synthesis of desymmetrized [2]catenanes with excellent translational selectivity

Desymmetrized [2]catenanes were synthesized and shown to exhibit excellent translational selectivity. The templated synthesis takes effect from the formation of pseudorotaxanes between pi-rich crown ethers and a pi-deficient pyromellitic (PmI) unit, followed by macrocyclization around the crown ethers with the creation of a bipyridinium (BPy) unit. The crown ethers preferably encircle the BPy unit in the resulting [2]catenanes in both solution and the solid state, as indicated by various spectroscopic analyses.     

Perfluorocyclobutyl-linked hexa-peri-hexabenzocoronene networks

Hexa-peri-hexabenzocoronene (HBC) derivatives possess many interesting properties ranging from liquid crystallinity, to hole transport, to variable emission behavior, yet are plagued by insolubility and general accessibility of polymerizable substituents. The first synthesis of trifluorovinyl ether-substituted hexabenzocoronene and its polymerization to perfluorocyclobutyl (PFCB) polymers and copolymers is shown. Unlike hydrocarbon ethers, fluoro vinyl ethers are stable under HBC oxidation conditions. Discrete HBC units in PFCB polymers provide access to potentially processable HBC optical materials.     

冠醚配合物的研究XV．若干席夫碱及仲胺型双冠醚和碱金属离子的配位反应

本文运用微量电导滴定及计算机拟合技术，研究了若干席夫碱及仲胺型双冠醚和减金属离子的配位反应，测定了配合物的组成及稳定常数，并对实验结果进行了讨论．     

冠醚配合物的研究XV.若干席夫碱及仲胺型双冠醚和碱金属离子的配位反应

本文运用微量电导滴定及计算机拟合技术，研究了若干席夫碱及仲胺型双冠醚和碱金属离子的配位反应，测定了配合物的组成及稳定常数，并对实验结果进行了讨论。     

p-Chlorophenyldiazonium hexafluorophosphate as a catalyst in the polymerization of tetrahydrofuran and other cyclic ethers

p-Chlorophenyldiazonium hexafluorophosphate is shown to be a convenient and effective catalyst for initiating the polymerization of tetrahydrofuran (TH) and other cyclic ethers. The polymerizations apparently proceed without any significant termination or transfer reactions (i.e., “living” polymers result), and materials of very high molecular weight can be obtained. A mobile monomer-polymer equilibrium for THF was obtained during polymerization and equilibrium conversions were determined at a number of temperatures. The ceiling temperature derived from these data was 84°C., the heat of polymerization was ?4.58 kcal./mole and the corresponding entropy change was ? 17.7 cal./°C.-mole. Hydrocarbons are suitable inert solvents for these polymerizations, but concentrated solutions must be used at ambient temperatures in order to stay above the required equilibrium monomer conceiitration and also to dissolve the catalyst which is insoluble in hydrocarbons. It was shown that acyclic ethers act as transfer agents in these polymerizations and that transfer with consequent reduction of molecular weight continues even after monomer-polymer equilibrium is reached. Cyclic ethers do not act as transfer agents but only copolymerize. Trimethyl orthoformate was shown to be a particularly effective transfer agent; it resulted in a polymer with methoxy endgroups and produced methyl formate as a by-product. The data obtained are consistent with a mechanism involving initiation by hydrogen abstraction and polymerization via tertiary oxonium ions associated with PF^?₆ gegenions. This gegenion is thought to be responsible for the “living” nature of the system.     

Metal-assisted reactions—13 : Rapid, slective reductive cleavage of phenolic hydroxyl groups by catalytic transfer methods

Previous work has shown that, after converting phenols into suitable phenolic ethers, the aromatic C---H bond of the original phenol can be reductively cleaved heterogeneously to give a C---H bond through the use of molecular hydrogen or hydrogen donors together with a transition metal catalyst. The present work provides a method for selectively replacing a phenolic OH group by H in just a few minutes, compared with the 2 to 4 hr required previously using a hydrogen donor and the several hours under pressure required for molecular hydrogen. Various kinds of groups are suitable for preparing the required phenolic ethers from phenols, but the best ones are strongly electro-withdrawing heteroaromatic entities. Solvent appears to play an important role in this heterogeneous reaction, the mechanism of which is discussed.     

Pyridino-armed diaza-crown ethers for specific transport of “transition metal cations”

A new series of double armed diaza-crown ethers, bearing pyridino- and quinolino-arm groups, were first shown to effectivelybind and transport some “transition metal cations” via three-dimensional complexations, which were not attained by common crown ethers.