Enzymatic resolution of sec-butylamine

Resolution of (±)-sec-butylamine by Candida antarctica lipase provided a very low enantiomeric excess of the residual amine when either ethyl or vinyl butyrate was used as the acylating agent. The enantiomeric excess was increased by using ethyl esters of long chain fatty acids. The rate of the reaction was increased by using methyl t-butyl ether as a solvent. (S)-sec-Butylamine of very high enantiomeric excess was obtained by C. antarctica lipase catalyzed acylation with ethyl decanoate in methyl t-butyl ether.     

Chiral base-catalyzed aldol reaction of trimethoxysilyl enol ethers: effect of water as an additive on stereoselectivities

An aldol reaction of trimethoxysilyl enol ether catalyzed by lithium binaphtholate is described. The aldol reaction of trimethoxysilyl enol ether derived from cyclohexanone under anhydrous conditions predominantly afforded the anti-aldol adduct with moderate enantioselectivity, whereas the reaction under aqueous conditions predominantly resulted in the syn-adduct and the enantioselectivity of the syn-adduct was considerably improved. The best enantioselectivity was obtained in the reaction of trimethoxysilyl enol ether derived from 1-indanone with cyclohexanecarboxaldehyde (97% ee (syn)). This is the first example of an aldol reaction of trimethoxysilyl enol ether catalyzed by a chiral base.     

Stereoelective radical copolymerization of (RS)-α-methylbenzyl vinyl ether with (S)-(-)- or (R)-(+)-N-(α-methylbenzyl)maleimide

Racemic α-methylbenzyl vinyl ether was copolymerized with optically active (S)-(-)- or (R)-(+)-N-(α-methylbenzyl)maleimide using 2,2′-azobisisobutyronitrile in order to examine the possibility of stereoelective radical polymerization of vinyl-type racemic monomers. The resulting copolymers were found to have almost alternating sequences of the two kinds of monomeric units. The non-polymerized α-methylbenzyl vinyl ether, recovered from the copolymerization system, showed an optical activity of opposite sign to the optically active comonomer used, indicating clearly that the co-polymerization process is stereoelective. It was confirmed that α-methylbenzyl vinyl ether preferentially incorporated in the copolymer has the same absolute configuration as the optically active N-substituted maleimide.     

Synthesis and chemistry of the phenoxasilins and dihydro-dibenzo-oxasilepins

Formation of both sila-functional and carbo-functional phenoxasilins from diphenyl ether and o,o′-dibromodiphenyl ether precursors is described. Tricyclic oxasilepins are formed from o,o′-dibromobenzylphenyl ether by metallation with n-BuLi followed by reaction with dichlorosilanes as well as by ring expansion of an appropriate phenoxasilin. Reactions at the silicon center and at the ring methylene carbon of the oxasilepins are reported, as well as attempts to generate oxasilocins.     

Claisen rearrangements—VII : Novel reactions of the coumarin,tomentin

The structure of tomentin has been confirmed as 5-hydroxy-6,7-dimethoxycoumarin (2), the derived 3,3-dimethylallyl ether giving a para-Claisen rearrangement product. Relief of strain in the corresponding 1,1-dimethylallyl ether has been found to result in a novel regiospecific ortho-Claisen rearrangement occurring on silica at room temperature. The structure 18 of the stable ortho-dienone formed has been confirmed by conversion of the corresponding dehydrodienone (15), obtained from the rearrangement of tomentin 1,1-dimethylpropargyl ether, to alloxanthoxyletin (25).     

Synthesis of symmetric HIJ-ring model of ciguatoxin

A tricyclic model ether compound comprising 6/8/6 ether rings was synthesized via a new route including conjugate addition to form a symmetric eight-membered ether-ketone with syn/trans stereochemistry in selective manner. The corresponding vinyl triflate of this ketone was allowed to convert to the vinyl methyl derivative via cross-coupling reaction. This endo-olefinic tetrahydro-2H-oxocin was selectively reduced to afford α-methyl product. The corresponding exo-olefinic oxocane derivative, on the other hand, provided the β-methyl isomer as the major diastereoisomer (2/1). Our previous report on the synthesis of this final product was revised due to some rearrangement and the mechanisms are discussed.     

Chemoselective ester/ether C–O cleavage of methyl anisates by aluminum triiodide

The aluminum triiodide mediated chemoselective ester/ether C–O cleavage of methyl anisates was investigated. o-Anisate undergoes ether cleavage at low temperatures in carbon disulfide, cyclohexane and acetonitrile. Further cleavage of the ester group occurs at elevated temperatures to afford salicylic acid. The cleavage of p-anisate is solvent-dependent. In cyclohexane, the ester and ether groups were cleaved non-selectively to give equimolar amounts of p-anisic acid and methyl p-hydroxybenzoate. The ester group was preferentially cleaved in acetonitrile, compared to ether group cleavage in carbon disulfide. The ester cleavage reaction was improved using pyridine as an acid scavenger additive. Reasons for the contrasting reactivity of anisates towards AlI₃ were explored, and the methods were applied to cleavage of the tert-butyl ester of acemetacin which gave different products under these conditions.     

Enzymatic resolution of 2-dialkylaminomethylcyclopentanols and -cycloheptanols

Extensive lipase screening was performed in relation to the asymmetric acetylation of rac-2-dialkylaminomethylcyclanols 1–5. The lipase PS- and Novozym 435-catalysed resolutions of compounds 1–5 were based on asymmetric acylation of the secondary OH group at the R-stereogenic centre with various vinyl esters, in different organic media. High enantioselectivity (E>200) was observed when vinyl acetate was used as acylating agent, with diethyl ether or with diisopropyl ether as solvent. The reaction rates were markedly affected by the size of the alicyclic ring, and by the solvent.     

Excess molar volumes,and excess molar enthalpies of (N-methyl-2-pyrrolidinone + an ether ) at the temperature 298.15 K

Excess molar volumes V_m^E have been calculated from measured density values over the whole composition range at T =  298.15 K and atmospheric pressure for six { N -methyl-2-pyrrolidinone  +  1,1-dimethylethyl methyl ether, or dipropyl ether, or 1,1-dimethylpropyl methyl ether, or diisopropyl ether, or dibutyl ether, or dipentyl ether}. Excess molar enthalpiesH_m^E were also measured for five { N -methyl-2-pyrrolidinone  +  1,1-dimethylethyl methyl ether, or dipropyl ether, or 1,1-dimethylpropyl methyl ether, or diisopropyl ether, or dibutyl ether} at T =  298.15 K and atmospheric pressure. The results are discussed in terms of intermolecular associations. The experimental results have been correlated with the UNIQUAC and NRTL equations.     

Synthesis of proposed structure of rennellianone B: A study on rearrangement of anthraquinonyl propargyl ether toward 2H-pyranoanthraquinone

Rennellianone B was originally reported as a natural 2H-pyranoanthraquinone, isolated from the root of Rennellia elliptica Korth. An efficient synthesis of the proposed structure of rennellianone B was accomplished, starting from alizarin. The key feature of the synthesis involves the Claisen rearrangement of the anthraquinonyl propargyl ether intermediate to provide a 2H-pyranoanthraquinone moiety. In addition, intensive studies on rearrangement reaction conditions of anthraquinonyl propargyl ether toward the 2H-pyranoanthraquinone skeleton were described.     

Structural studies of organometallic compounds in solution: I. Magnesium iodide in diethyl ether and tetrahydrofuran

The structure of 2.8 M MgI₂ in diethyl ether solution and that of 1.7 M MgI₂ in tetrahydrofuran solution have been determined by large angle X-ray scattering measurements. The measurement on the diethyl ether solution was performed at 44°C, on a phase crystallizing at approximately 30°C. In diethyl ether a dimeric structure is found, arranged in a square-planar fashion. The bond lengths are: MgI 2.652(2), II (diagonal) 3.75(2) and II (linear) 5.30 Å. Three diethyl ether molecules are probably coordinated to each magnesium to complete an octahedral arrangement. In tetrahydrofuran the ion MgI⁺ from a dissociated complex predominates. In the MgI₂ complex a tetrahedral arrangement is found. In both the MgI⁺ and MgI₂ complexes the MgI distance is 2.56(2) Å. In the MgI₂ complex the II distance is 4.44(4) Å. In both solutions the MgO and MgC distances were kept fixed at 2.10 and 3.48 Å, respectively. The solubility of MgI₂ in diethyl ether has been shown to be strongly dependent on the water content of the ether; 0.2 M was the highest concentration obtained in anhydrous diethyl ether.     

Interfacial behavior of phase transfer catalysis of the reaction between potassium thiocyanate and p-nitrobenzyl bromide with crown ethers as catalysts

A very simple and novel method is devised to study the mechanism of phase transfer catalysis (PTC) for a nucleophilic substitution reaction between potassium thiocyanate and p-nitrobenzyl bromide (p-NB); the mechanism of the nucleophilic substitution reaction is illustrated by characterizing the interfacial dilational viscoelastic properties of the crown ether catalysts and intermediates, which are closely related to the interfacial behavior of the species in the PTC reaction. The results obtained from this study can be used to infer the mechanism of the nucleophilic substitution reaction that uses 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) as phase transfer catalysts. This mechanism begins with formation of the intermediates [K · Crown ether]⁺ and [K · Crown ether]⁺SCN^? through mutual collisions between crown ethers and KSCN in the aqueous phase near the interface. Then the complex, [K · Crown ether]⁺Br^?, was obtained due to the collision between [K · Crown ether]⁺SCN^? and p-NB in the organic phase near the interface and simultaneously the products were obtained.     

Synthesis of perfluoro-t-butyl trifluorovinyl ether and its copolymerization with TFE

Perfluoro-t-butyl trifluorovinyl ether (CF₃)₃COCFCF₂ was prepared by the addition of perfluoro-t-butyl hypofluorite (CF₃)₃COF to 1,2-dichloro-1,2-difluoroethylene followed by dechlorination. The obtained trifluorovinyl ether monomer readily copolymerizes with TFE in the presence of a radical initiator.     

Claisen rearrangements—V : Synthesis of the coumarins,dentatin (poncitrin) and glabralactone (angelicone)

Dentatin (= poncitrin) (1) has been synthesised from clausenidin methyl ether (10), the latter coumarin being obtained by Claisen rearrangement of the 3,3-dimethylallyl ether (8) derived from the chromanone (7). The synthesis of glabralactone (17) has been achieved from the methyl ether of 7via retro-Michael chromanone ring opening, and coumarin ring isomerisation. The structure of angelicone is reassigned as 17.     

Carbocyclization of d-glucose: syntheses of gabosine I and streptol

d-Glucose was differentially protected with a trans-diacetal at C-2,3, an ethoxymethyl ether at C-4, and a tert-butyldimethylsilyl ether at C-6, and then carbocyclized via a key Horner-Wadsworth-Emmons (HWE) olefination to give a versatile synthetic intermediate, enone 13, which was readily transformed into gabosine I and streptol.     

Bis(oxazoline)–ligand-mediated asymmetric [2,3]-Wittig rearrangement of benzyl ethers: reaction mechanism based on the hydrogen/deuterium exchange effect

We have investigated the mechanism of chiral induction in the asymmetric [2,3]-Wittig rearrangement of allyl benzyl ether in the presence of a bis(oxazoline) chiral ligand [(S,S)-Box–tBu] by comparing the reaction of both enantiomers of monodeuterated benzyl ether 1a–d. As a result, we found that chirality was induced via enantioselective deprotonation followed by efficient chirality transfer of the resulting chiral benzyl carbanion with the inversion of stereochemistry. It was revealed that the chiral ligand facilitates selective deprotonation as well as prevents the chiral carbanion from racemization. Moreover, we examined the effect of the o-methoxy substituent on the benzene ring.     

Electrochemical fluorination of chlorine-containing ethers

The electrochemical fluorination of chlorine-containing ethers has been studied. In general, it was found that a chlorine bonded to an a-carbon atom in the ethers was readily removed during electrochemical reaction in anhydrous hydrogen fluoride, whilst a chlorine bonded to the β-carbon atom was retained to yield β-chlorinated polyfluoroethers.Through the use of this method, several new chloropolyfluoroethers, e.g. 2-chloro-1,1,2,2-tetrafluoroethyl difluoromethyl ether, 2,2-dichloro-1,1,2-trifluoroethyl trifluoromethyl ether 2,2-dichloro-1,1,2-trifluoroethyl difluoromethyl ether, 2,2-dichloro-1,1,2-trifluoroethyl chlorodifluoromethyl ether, 2-chloro-1,1,2,2-tetrafluoroethyl chlorodifluoromethyl ether and 2,2-trichloro-1,1-difluoroethyl trifluoromethyl ether, have isolated and characterized.     

Metal-free synthesis of reactive oligomers by ring-opening oligomerization of glycidyl phenyl ether initiated with tetra-n-butylammonium fluoride in the presence of various protic compounds

Metal-free ring-opening oligomerizations of glycidyl phenyl ether (GPE) were performed with tetra-n-butylammonium fluoride (n-Bu₄NF) as an initiator in the presence of protic compounds (RHs) as chain transfer agents (CTAs). The RHs having pKa between 4.66 and 15.5 enabled to serve as the CTA in this oligomerization system, leading to reactive oligomers with relatively controlled molecular weights having narrow molecular weight distributions bearing functional groups such as alkene, benzyl ether, alkyne, ester and methacrylate groups at initiating end.     

Experimental liquid–liquid equilibria of 1-methylimidazole with hydrocarbons and ethers

The liquid–liquid equilibria (LLE) of eight binary systems containing 1-methylimidazole and n-alkanes (n-pentane, n-hexane), cyclohydrocarbons (cyclopentane, cyclohexane), aromatic hydrocarbons (hexylbenzene) or ethers (di-n-propyl ether, di-n-butyl ether, di-n-pentyl ether) have been measured from 270 K to the boiling temperature of the solvent using a “cloud point” method. Experimental solubility results are compared with values calculated by means of the NRTL equation utilizing parameters derived from LLE results.Solubility of 1-methylimidazole in many other organic solvents (aromatic hydrocarbons, branch chain ethers and ketones) has been measured at temperatures higher than 293 K and no miscibility gap was observed. The interaction of 1-methylimidazole with different solvents is discussed.     

P-stereogenic wide bite angle diphosphine ligands

Two modular synthetic approaches for the preparation of novel wide bite angle diphosphine ligands containing stereogenic P-atoms have been developed, leading to compounds (S,S)-2,2′-bis(methylphenylphosphino)diphenyl ether (L1) and (S,S)-2,2′-bis(ferrocenylphenylphosphino)diphenyl ether (L2) in very good diastereomeric ratios. Both protocols involve diphenyl ether as backbone and (2R_P,4S_C,5R_C)-(+)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine borane (R_P)-5 as initial auxiliary to induce chirality at phosphorus. The absolute configuration of intermediates (S,S)-9-(BH₃)₂ and (R,R)-10-(BH₃)₂ as well as the ligands (S,S)-L1-BH3 and (S,S)-L2 was determined by X-ray crystallographic analysis.