bluuebunny/crossref_metadata_2025_split huggingface dataset:
The IR Photochemistry of Organic Compounds. II. The IR Photochemistry of Ethers: The Decomposition Patterns
Authors: Majima Tetsuro , Ishii Tadahiro , Arai Shigeyoshi 
Published: July 2006

Abstract
The infrared multiple-photon decomposition (IRMPD) of saturated open-chain ethers has been systematically investigated with the intention of establishing their decomposition patterns. The main products in the IRMPD of ethers (1a–f, 2) are H2CO, CO, H2, and lower hydrocarbons. Acetaldehyde is additionally formed in the IRMPD of 1b and 1d, while acetone is formed in the IRMPD of 1d. The observed results are explained on the basis of the decomposition of the highly vibrationally excited ethers produced in the IRMP excitation. The initial process is the homolytic cleavage of a C–O bond to yield the corresponding alkyl and alkoxyl radicals. The alkyl radicals are trapped by Br2. Sequential splitting and addition reactions of the radicals yield primary products with a high internal energy. The primary products also decompose sequentially into stable products, in part. The sequential processes compete with collisional deactivation. Therefore, the branching ratio depends on the internal energy of the radicals and the primary products.
Relationships between Mesophase Behavior and Crystal Structures of Chiral Smectogenic 4-[(S)-2-Methylbutyl]phenyl 4′-Alkoxybiphenyl-4-carboxylates
Authors: Hori Kayako , Takamatsu Miho , Ohashi Yuji 
Published: July 2006

Abstract
Interlayer distances of Sm*C and Sm A phases of the title series were measured as functions of temperature by X-ray diffraction. With increase in temperature, molecular tilt angles in Sm*C decrease from 22–25 to 0°. Crystal structures of the heptyl (1) and octyl (2) homologues have been determined by X-ray analysis. (1): 4-[(S)-2-Methylbutyl]phenyl 4′-heptyloxybiphenyl-4-carboxylate, monoclinic, P21, a=26.929(4), b=5.4249(5), c=9.2607(9) Å, β=96.78(1)°, Z=2. (2): 4-[(S)-2-Methylbutyl]phenyl 4′-octyloxybiphenyl-4-carboxylate, orthorhombic, P212121, a=9.249(1), b=56.259(9), c=5.412(1) Å, Z=4. Final R were 0.076 and 0.121, respectively. Both crystals have distinct layer structures similar to those of Sm*C. In the former crystal, the molecules tilt to one direction uniformly throughout layers, while in the latter, they take two opposite directions alternately from layer to layer. However, structures within a layer are very similar to each other. Each molecule has a coplanar biphenyl moiety and a twisted paraffin chain. Mesophase behavior was interpreted very well by the molecular interaction revealed in the crystal structures.
Preparation and Properties of the σ-Picolyl Complexes of Palladium(II), [{PdCl(C5H4N-2-CH2)PPh3–nMen}2] (n=0, 1, and 2)
Authors: Isobe Kiyoshi , Nakamura Yukio , Kawaguchi Shinichi 
Published: July 2006

Abstract
The oxidative addition of 2-(chloromethyl)pyridine to tetrakis(triphenylphosphine)palladium(0) in toluene at 100 °C gave [{PdCl(C5H4N-2-CH2)PPh3}2] (1a), which was characterized by analytical, molecular-weight, and IR data as well as 1H, 31P, and 13C NMR spectroscopy. The chloride ligand was readily replaced by other halides, whereas tertiary phosphines such as diphenylmethyl-, phenyldimethyl-, and triethylphosphines cleaved the bridge after substitution of triphenylphosphine to result in the monomeric trans-[PdCl(C5H4N-2-CH2)(PR3)2] complexes. Reactions of 1a with carbon monoxide and other reagents are also reported. The corresponding 3-picolyl complex [{PdCl(C5H4N-3-CH2)PPh3}n] was also prepared, but could not be well characterized because of lower stability and solubility.
Single Crystal X-Ray and Optical Studies on Bis(1,5-diazacyclooctane)copper(II) Nitrate, a Thermochromic Copper(II) Complex Involving Hydrogen Bonds between the Ligand and the Counter Ion
Authors: Hoshino Naomi , Fukuda Yutaka , Sone Kozo , Tanaka Kiyoaki , Marumo Fumiyuki 
Published: July 2006

Abstract
A thermochromic copper(II) complex of 1,5-diazacyclooctane (daco), [Cu(daco)2](NO3)2, has been subjected to single-crystal X-ray and optical studies. This complex is orange as isolated, but it turns violet discontinuously when heated above 90 °C and returns to orange on cooling. Crystal structure of the low-temperature form has been determined at room temperature; the complex crystallizes in the monoclinic space group P21⁄n with a=7.9040(7), b=15.694(1), c=7.0886(7) Å, β=95.36(1)°; V=875.5(1) Å3, and Z=2. The CuN4 chelate plane is planar and Cu–N coordination bonds are rather short. The structure has revealed the presence of weak hydrogen bonds bridging imino groups of the ligands with the nitrate ions and forming a macrocycle-like ring system, which results in enhancement of the ligand field strength. Single-crystal visible and infrared spectra for both low- and high-temperature forms have heen obtained and compared. A high-energy d–d transition band(s) causing the orange color at room temperature is in contrast to an extremely flattened broad band(s) for the violet form. The IR spectra of the two forms clearly differ in the intensity of νNH stretching peak, implying that the thermochromic phase transition involves a change in the nature of the hydrogen bonds of the imine ligands. On the basis of these observations and comparison to reported studies on a similarly thermochromic copper(II) complex, a mechanism is suggested involving dynamic fluctuation of the ligand field and geometry due to thermal motion of the anion/ligand hydrogen bond system.
Synthesis and Properties of Copper(II) Perchlorate Complexes with Imino Oximes
Authors: Wan Songping , Mori Wasuke , Yamada Shoichiro , Murahashi Shun-Ichi 
Published: July 2006

Abstract
Three types of imino oxime copper(II) complexes were obtained by the reactions of copper(II) perchlorate with imino oximes (3-[2-[(alkylamino)ethyl]imino]-2-butanone oximes or 3-[2-[(dialkylamino)ethyl]imino]-2-butanone oximes, abbreviated as Hdox-enRR′). One type contains the dinuclear complexes [Cu2(dox-enRR′)2]2+ and uncoordinated perchlorate anions. The magnetic susceptibilities measured over the temperature range 77–320 K indicate that there exists a strong antiferromagnetic spin coupling interaction through the N–O bridge in these complexes. The magnetic behavior can be explained by using the Bleaney–Bowers equation. Complexes of the second type probably contain a square-tetranuclear complex. The copper(II) ions assume a penta-coordinated configuration with perchlorate anion coordinated at the axial coordination site. It is assumed that the dinuclear and mononuclear magnetic units coexist in the complexes of the third type. The plot of the magnetic susceptibilities versus temperature is linear in the two temperature ranges (T&gt;250 K, &lt;100 K).
Microbiosensing Device for Real Time Determination
Authors: Ikariyama Yoshihito , Shimada Naoki , Yukiashi Tomoaki , Aizawa Masuo , Yamauchi Shigeru 
Published: July 2006

Abstract
A microbiosensing device fabricated by assembling an enzyme-embodied microelectrode with a counter electrode and a reference electrode was applied to the real time determination of trace droplet of glucose sample. The microdevice demonstrated unique properties such as real time response, independence of sample volume, unnecessity of sample mixing by the rendezvous of microfabricated biosensing device with pulse voltammetry. A linear relationship between sensor output and glucose concentration was obtained in the concentration range from 10−3 to 10−1 mol L−1. The sensing device responded to every glucose sample of different concentration in 2 ms, and the coefficient of variation for 10 mM glucose determination was within 5%.
Micro-Enzyme Electrode as a High-Performance Detector of Flow Injection Analysis
Authors: Ikariyama Yoshihito , Yamauchi Shigeru , Yukiashi Tomoaki , Ushioda Hiroo , Aizawa Masuo 
Published: July 2006

Abstract
The advantages of miniaturized enzyme electrode have been applied to flow injection analysis for the development of a rapid and selective method for the continuous determination of glucose. By assembling a micro-enzyme electrode having a diameter of 10 μm for an amperometric flow-through detector, at least 600 glucose samples can be determined in one hour. And micro-enzyme electrodes are satisfactorily stable for over 4 weeks even after 1000 glucose injections.
Oxidation of Lipids. XVI. Inhibition of Autoxidation of Methyl Linoleate by Diarylamines
Authors: Takahashi Mareyuki , Tsuchiya Jyunichi , Niki Etsuo 
Published: July 2006

Abstract
The inhibition of oxidation of methyl linoleate in homogeneous solution and in aqueous dispersions by diarylamines has been studied. Diphenylamines with electron-donating substituents exhibited antioxidant activities, while those having electron-withdrawing substituents such as niflumic acid and flufenamic acid did not suppress the oxidation appreciably. When both 4,4′-dimethoxydiphenylamine and α-tocopherol were present as antioxidants, only α-tocopherol was consumed at first and when α-tocopherol was almost completely depleted, 4,4′-dimethoxydiphenylamine began to be consumed to give nitroxide radical, which further acted as antioxidant.
Oxidation of Lipids. XVII. Crossover Effect of Tocopherols in the Spontaneous Oxidation of Methyl Linoleate
Authors: Takahashi Mareyuki , Yoshikawa Yasuyuki , Niki Etsuo 
Published: July 2006

Abstract
Tocopherols suppressed the spontaneous, thermal oxidation of methyl linoleate and produced a clear induction period. During the induction period, small amounts of cis,trans-hydroperoxides were formed but the formation of trans,trans-hydroperoxides was almost completely inhibited. Tocopherols were consumed and when they were depleted, the induction period was over and a fast oxidation proceeded to give more trans,trans-hydroperoxides than cis,trans-hydroperoxides. However, tocopherols, especially α-tocopherol, acted as prooxidants when their concentrations were extraordinarily high and the rate of initial radical formation was low. The reducing agent such as ascorbic acid diminished the prooxidant action of α-tocopherol. This prooxidant effect of tocopherols was ascribed to the spontaneous formation of tocopheroxyl radical followed by the hydrogen atom abstraction by the tocopheroxyl radical from the hydroperoxide to give a peroxyl radical.
Synthesis of a Protected Sperm Whale Myoglobin-(77–96)-Eicosapeptide and Circular Dichroism Spectra of the Related Peptides
Authors: Hashimoto Chikao , Muramatsu Ichiro 
Published: July 2006

Abstract
A protected sperm whale myoglobin-(77–96)-eicosapeptide (23) was synthesized by a solution method. The protected peptide 23 could be effectively purified by silica-gel column chromatography with 1-butanol–acetic acid–water as the eluate. The CD spectra of protected fragment peptides were measured in a solution of 2,2,2-trifluoroethanol. A protected sperm whale myoglobin-(85–96)-dodecapeptide and 23 showed CD profiles characteristic of a helical structure.
Replacement of an 11-Carbonyl Group of 11-Oxo Steroid by an Oxygen Atom. A New Partial Synthesis of 11-Oxaprogesterone
Authors: Suginome Hiroshi , Wang J B 
Published: July 2006

Abstract
We describe the transformation of commercially available 3α-hydroxy-5β-pregnane-11,20-dione acetate (1) into 11-oxaprogesterone (15) in 11 steps including the regioselective β-scission of an alkoxyl radical as a key step.
The Formation Pathway of 3,5-Bis(methoxymethyl)perhydro-1,3,5-oxadiazin-4-one
Authors: Shiba Ryuichi , Takahashi Miyuki , Ebisuno Toichi , Takimoto Michiaki 
Published: July 2006

Abstract
The investigation of the reactions of urea and its methyl derivatives with formaldehyde elucidated the formation pathway of 3,5-bis(methoxymethyl)perhydro-1,3,5-oxadiazin-4-one. 1) The addition of formaldehyde to urea became increasingly difficult according to the increase of the number of added formaldehyde molecules, probably because of the steric hindrance of the hydroxymethyl groups. 2) 3,5-Bis(methoxymethyl)perhydro-1,3,5-oxadiazin-4-one was concluded to be derived from urea via tris(hydroxymethyl)urea and 3-(hydroxymethyl)perhydro-1,3,5-oxadiazin-4-one but not via tetrakis(hydroxymethyl)urea or perhydro-1,3,5-oxadiazin-4-one.
Stereochemistry of a Chiral Germyl Radical in the Reaction of Carbon Tetrachloride
Authors: Mochida Kunio , Yamauchi Takato , Sakurai Hideki 
Published: July 2006

Abstract
A chiral germyl radical produced from an optically active hydrogermane, 1-NpPhMeGe*H, abstracted a chlorine atom from CCl4 to give the corresponding chlorogermane with retention of configuration. Progressive dilution of CCl4 with cyclohexane demonstrated that the chiral germyl radical could also undergo inversion. A mechanism in which inversion of the chiral germyl radical competed with chlorine abstraction was proposed and the relative rate of chlorine abstraction to inversion (kCl⁄kinv) of the chiral germyl radical was found to be (0.52±0.13) mol−1 dm3 at 80 °C. The rate constant for the chlorine abstraction (kCl) by germyl radicals with CCl4 was determined to be (6.6±1.0)×108 s−1 mol−1 dm3 by laser-photolysis experiments. By using this rate constant, the kinv value for the chiral germyl radical was estimated to be ca. 2×109 s−1.
Synthesis of Nonadeca- and Octadecaribonucleotides Using the Solid-Phase Phosphotriester with Tetrahydropyranyl Groups as the 2′-Hydroxyl-Protecting Group
Authors: Hirao Ichiro , Ishikawa Masahide , Hori Hiroyuki , Watanabe Kimitsuna , Miura Kin-ichiro 
Published: July 2006

Abstract
Nonadeca- and octadecaribonucleotides corresponding to the D-loop of tRNAPhe from yeast and the leader sequence of phage f1 coat protein mRNA were synthesized by the activated phosphotriester method. Coupling yield in the synthesis of oligoribonucleotides depended on the extent of nucleosides loaded on controlled pore glass beads (CPG). N-Acyl-5′-O-dimethoxytrityl-2′-O-tetrahydropyranyl derivatives were used as fully protected ribonucleotide monomer units. The 18mer and 19mer corresponding to the D-loop did not serve as substrates for tRNA (guanosine-2′-)methyltransferase from T. thermophilus, but inhibited methylation of the 5′-half fragment of tRNAPhe. This indicates that both fragments possess some affinity with the enzyme.
Uranyl Ion as a Highly Effective Catalyst for Internucleotide Bond Formation
Authors: Sawai Hiroaki , Kuroda Kensei , Hojo Takashi 
Published: July 2006

Abstract
Uranyl ion catalyzes the polymerization of adenosine-5′-phosphorimidazolide very efficiently in aqueous solution. Up to 95% of the input adenosine-5′-phosphorimidazolide is converted to oligoadenylates from dimer to hexadecamer when 1 mM of UO22+ is used as a catalyst. The oligomeric products are predominantly 2′–5′ linked. The chain length and the regioselectivity of the resulting oligoadenylates varies greatly with the concentration of the UO22+ ion catalyst and the pH of the reaction medium. A high total yield of oligouridylates up to dodecamer is also obtained by UO22+ ion catalyst with high 2′–5′ regioselectivity. The oligonucleotide formation is mediated by UO22+-nucleotide complex.
Ring-Opening Fluorination and Ring-Expansion Fluorination of Cyclopropanemethanols with Amine/Metal Fluoride/Poly(hydrogen fluoride)–Pyridine Complex
Authors: Kanemoto Shigekazu , Shimizu Makoto , Yoshioka Hirosuke 
Published: July 2006

Abstract
Treatment of cyclopropanemethanols with pyridinium poly(hydrogen fluoride) in the presence of diisopropylamine and KHF2 gave selectively homoallylic fluorides or fluorocyclobutanes according to the mode of substitution of the starting cyclopropanemethanols. Cyclopropanemethanols with no substitution at 1-position of the cyclopropane ring gave homoallylic fluorides in a stereoselective manner. While, 1-methylcyclopropanemethanol gave the fluorocyclobutane in high stereoselectivity. Fluorocyclobutanes containing hydroxy methyl group were also prepared from 2-(1-methylcyclopropyl)oxiranes. The amine and the metal fluoride were necessary as additives for the best results. Influencing factors involving solvents and temperature for the reactions are also described.
Substrate Selectivity of Artificial Transaminase Constituted with Functionalized Bilayer Membrane
Authors: Murakami Yukito , Kikuchi Jun-ichi , Shiratori Nobuyuki 
Published: July 2006

Abstract
The transamination reactions of α-amino acid derivatives with α-keto acids as catalyzed by an artificial transaminase were examined in aqueous media under mild conditions. The present artificial holoenzyme was constituted with a combination of a cationic peptide lipid having a l-histidyl residue, a hydrophobic pyridoxamine derivative, and copper(II) ions, and found to exercise marked substrate selectivity which came from the molecular recognition in the course of formation of the aldimine Schiff-base chelates composed of the hydrophobic pyridoxal derivative, α-amino acids, and copper(II) ions. The transamination reaction of the hydrophobic β-benzyl l-aspartate with the hydrophilic pyruvate was most effectively catalyzed among 18 combinations of substrate species employed here. Enantioselectivity was observed for the catalytic transamination of phenylalanine with pyruvate.
The Electrolytic Reduction of p-Substituted α-(Methylsulfinyl)-α-(methylthio)acetophenones in Acetonitrile
Authors: Kunugi Akira , Takahashi Norimasa , Abe Kyo , Hirai Taketsugu 
Published: July 2006

Abstract
p-Substituted α-(methylsulfinyl)-α-(methylthio)acetophenones (1) exhibit, on polarographic reduction, three waves. The two last waves correspond to the reductions of p-substituted α-(methylthio)acetophenones (2) and p-substituted acetophenones respectively. The macroelectrolysis at the first wave potential results in the formation of 2 in good yields in the presence of benzoic acid. The electrolytic reduction of 1 is characterized by the elimination of the methylsulfinyl group rather than by the deoxygenative reduction of the sulfoxide to the sulfide or the reduction of the carbonyl group.
Photooxidation of Bis[1,2-diphenylethanedithione]nickel(0)tetrabutylamine with α-Tocopherol
Authors: Enmanji Koe 
Published: July 2006

Abstract
The photooxidation of a nickel dithiolate complex by α-tocopherol was found for the development of a recording medium which can be used to read by a laser diode. The mechanism was analyzed. As a result, it was found that α-tocopherol produced oxygen adducts by light; the oxygen adducts oxidized bis[1,2-diphenylethanedithione]nickel(0)tetrabutylamine.
Metastable Dissociations of CH3NO2+ and CD3NO2+ Ions. Isotope Effects of the Loss of a Hydroxyl Radical
Authors: Arakawa Ryuichi 
Published: July 2006

Abstract
A large kinetic isotope effect has been observed for the metastable transitions of CX3NO2+→CX2NO++OX (X=H, D). The large effect was explained by assuming a rate-determining isomerization to an aci-nitromethane ion and the quantum mechanical tunneling of a hydrogen atom.
A Molecular Orbital Study of Cyclodextrin Inclusion Complexes, II. The Structural Analysis of α-Cyclodextrin Inclusion Complex with m-Nitrophenol in Aqueous Solution Based on the Quantum-Chemical Solvation Theory
Authors: Sakurai Minoru , Kitagawa Masaki , Hoshi Hajime , Inoue Yoshio , Chûjô Richirô 
Published: July 2006

Abstract
The host–guest orientation and the position of the guest m-nitrophenol (MNP) in the α-cyclodextrin(α-CD)–MNP complex in aqueous solution have been determined by comparing the complexation-induced 13C NMR chemical shifts of MNP with those predicted by quantum chemical calculation. The results are consistent with the X-ray data of this complex.
Effects of Pressure on Hydrolysis of p-Nitrophenyl Acetate in Aerosol OT Reversed Micelles
Authors: Tamura Katsuhiro , Yoshinari Mami 
Published: July 2006

Abstract
Kinetic studies were made on imidazole-catalyzed hydrolysis of p-nitrophenyl acetate in Aerosol OT (AOT) reversed micelles (AOT/H2O/heptane) at high pressure. The rate of the reaction was found to increase with increase in the size of the aqueous core in the reversed micelles and with increase in pressure. Micellar effects on the hydrolysis are discussed in relation with the activation parameters of the reaction.
Optical Resolution of Di-2-pyridylamine Complexes of Ruthenium(II)
Authors: Fukuchi Takashi , Nagao Noriharu , Miki Eiichi , Mizumachi Kunihiko , Ishimori Tatsujiro 
Published: July 2006

Abstract
Through SP-Sephadex ion exchange chromatography [Ru(Hdpa)3]2+ and [Ru(bpy)2(Hdpa)]2+ (Hdpa=di-2-pyridylamine) were resolved by the use of an aqueous sodium d-tartrate solution as the eluting agent. Λ-[Ru(Hdpa)3]2+ and Δ-[Ru(bpy)2(Hdpa)]2+ were eluted in the early fractions. The precipitation of diastereomers with dibenzoyl-d-tartrate was also successful in the resolution of [Ru(Hdpa)3]2+ and [Ru(bpy)(Hdpa)2]2+. The absolute configurations of the complexes were assigned by referring to the signs of CD spectra at around 3.2–3.8 μm−1.
The Crystal and Molecular Structures of Tetraethylammonium [Heptakis(isothiocyanato)lanthanate(III) and -praseodymate(III)]·Benzene, [(C2H5)4N]4[M(SCN)7]·C6H6 (M=La, Pr), in a Unicapped Trigonal Prism Geometry
Authors: Matsumoto Fumiko , Takeuchi Toshio , Ouchi Akira 
Published: July 2006

Abstract
The crystals of the title new lanthanum(III) complex, LaC45H86N11S7, F.W. 1144.59 are orthorhombic space group Bm21b, a=17.438(7), b=21.507(9), c=16.616(6) Å, U=6232(4) Å3, Dm=1.21(3), Dx=1.22 g cm−3, and μ(Mo Kα)=9.63 cm−1. The central lanthanum(III) atom has a unicapped trigonal-prism 7N-hepta-coordination geometry: seven thiocyanato nitrogen atom are ligated. There are no bridgings between the complexes and/or counter cations. Each benzene molecule is surrounded by the thiocynate ions and ethyl groups of the cations. Although these crystals lose benzene at about 60 °C, they are stable for more than several weeks ambient temperature, and can be regarded as a kind of inclusion compound. The isomorphous praseodymium(III) complex was also obtained.
The Fluorometric Determination of Magnesium with 2,2′-Dihydroxy-4,4′-dimethylazobenzene
Authors: Aoki Izuo , Saito Atsushi , Watanabe Kunihiro 
Published: July 2006

Abstract
In an alkaline medium, magnesium reacts with 2,2′-dihydroxy-4,4′-dimethylazobenzene to emit a strong fluorescence, which is about 5 times as intense as that obtained with its parent compound (2,2′-dihydroxyazobenzene). Nonextraction (water–ethanol–dioxane, a mixed solvent) and extraction (an isopentyl alcohol solvent) procedures for the fluorometric determination of magnesium with this reagent were established. 0.1 μg to 4.0 μg of magnesium can be rapidly determined by the nonextraction procedure. In the extraction procedure, 1000-fold excesses of calcium did not interfere even when no masking agent was used.
Rotational Isomerism in Fluorene Derivatives. XVI. Conformational Equilibria of 9-Substituted 9-(2′-Bromomethylphenyl)fluorene Derivatives
Authors: Nishida Akiko , Shirakawa Shinsuke , Yamamoto Masuji , Watanabe Shigeki , Fujisaki Shizuo , Kajigaeshi Shoji 
Published: July 2006

Abstract
(Eight 9-substituted 9-(2′-bromomethylphenyl)fluorene derivatives) (1) were prepared. Their conformational equilibria (ap\ightleftarrowssp) are discussed on the basis of kinetic data for internal rotation obtained by 1H NMR spectroscopy.
Tellurium-Assisted Cyclopropanation and Alkylidenation of α,β-Unsaturated Carbonyl Compounds with Dibromomalonic Esters
Authors: Matsuki Toshiaki , Hu Nan Xing , Aso Yoshio , Otsubo Tetsuo , Ogura Fumio 
Published: July 2006

Abstract
Dibutyl telluride assists cyclopropanation of α,β-unsaturated ketone, ester, and nitrile with dibromomalonic esters without solvent at room temperature. In addition, it effects alkylidenation of aldehydes including α,β-unsaturated aldehyde with the same reagent.
The Utility of t-Butyldimethylsilane as an Effective Silylation Reagent for the Protection of Functional Groups
Authors: Yamamoto Keiji , Takemae Makoto 
Published: July 2006

Abstract
Treatment of compounds containing functional groups, such as alcohols, amines, and carboxylic acids, with t-butyldimethylsilane in the presence of a catalytic amount of palladium on carbon is described to provide a new, convenient method for the introduction of a t-butyldimethylsilyl (TBDMS) group.