Combined gas chromatography-mass spectrometry of the inositol trimethylsilyl ethers and acetate esters

Each of the inositol diastereomers have been subjected to low resolution gas chromatography-mass spectrometry as their hexa-O-trimethylsilyl (TMSi) ethers and as their hexaacetyl esters. The TMSi ethers of the inositols each possess a unique spectrum consisting of the same ions occurring with remarkable variation in intensity. This variation, which is much greater with the inositol TMSi ethers than in the spectra of the inositol acetates, is presumably an expression of the stereochemistry of each isomer exaggerated by the bulky TMSi groups. Using TMSi-d₉, labeling as well as ring labeling with deuterium we identified several fragment ions which are characteristic of the cyclitols. The spectra of the TMSi inositols are compared with the spectra of other TMSi carbohydrates. Two main series of fragmentation processes are observed in the inositol hexaacetates. With the aid of acetyl-d₃ labeling each of these series were found to divide into two more pathways consisting of ions of the same m/e values but of different structures. These pathways are compared with similar pathways observed in other acetyl carbohydrates. A method is described for the direct conversion of TMSi ethers to acetate esters which has potential usefulness in natural product studies.     

A novel aminomethylation of silyl enol ethers with aminomethyl ethers catalyzed by iodotrimethylsilane or trimethylsilyl trifluoromethanesulfonate

The iodotrimethylsilane-catalyzed reaction of silyl enol ethers with aminomethyl ethers in acetonitrile gives aminomethylation products of the corresponding ketones readily. The reaction can slso be catalyzed by trimethylsilyl trifluoromethanesulfonate in dichloromethane.     

NH4Cl.CrO3对烯丙基醚和苄基醚的选择性氧化成酯的研究

本文报道了NH4Cl.CrO3(简称ACC)在无溶剂反应条件下, 以较好的产率, 将烯丙基醚或苄基醚选择性地氧化成相应的酯。     

Protonation of acetyl and formyl derivatives of pyrrole

By electronic spectroscopy and PMR spectroscopy it has been shown that the protonation of derivatives of - and -acetylpyrroles and the corresponding formylpyrroles in 14–26 N H₂SO₄ takes place at the oxygen atom of the carbonyl group. The derivatives substituted by an alkyl group (CH₃, C₂H₅) in position 4 have a similar structure of the conjugate acids in concentrated H₂SO₄. Under the same conditions, the derivatives not substituted in position 4 are capable of adding a proton to C₄ of the pyrrole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1498–1504, November, 1973.     

Removal of methoxyethoxymethyl ethers with trimethylsilyl chloride-sodium iodide

Trimethylsilyl chloride-sodium iodide has been used for the mild removal of methoxyethoxymethyl ethers.     

CAN/[nbp]FeCl4 as a reusable catalytic system for direct conversion of trimethylsilyl ethers to their acetates under microwave irradiation

A rapid and easy procedure for direct conversion of TMS-ethers to their acetates catalyzed by cerium(IV) ammonium nitrate (CAN) immobilized on n-butylpyridinium tetrachloroferrate ([nbp]FeCl₄) as a room temperature ionic liquid under microwave irradiation was developed. This methodology is enough mild so that the acid sensitive groups such as methoxy, furyl or thiophenyl were remained intact. No side products were observed by this method.     

Reaction of acetals and trialkylsilanes catalyzed by trimethylsilyl trifluoromethanesulfonate. A simple method for conversion of acetals to ethers

A mild, catalytic procedure for converting acetals to ethers is described.     

An efficient method for the reductive conversion of acyclic esters to ethers via a TMS-protected acetal

We report an efficient two step process for the reduction of non-aromatic esters to the corresponding ethers via the intermediate TMS-protected acetal. The acetal formed after the first step can be carried on directly to the subsequent reduction to the ether without purification. The ester reduction step was monitored using in-situ ReactIR for disappearance of the CO peak, allowing for the exact determination of time and equivalents of the reducing agent. Furthermore, use of TMS-imidazole to form the acetal has allowed us to dramatically reduce the overall reaction time required for the two step procedure.     

Conformational analyses for acetyl and formyl ligands bound to transition metal auxiliaries

Conformational analyses for acetyl and formyl ligands bound to transition metal auxiliaries reveal that, after considering primary stereoelectronic effects where appropriate, the conformations adopted by acetyl ligands are determined primarily by steric interactions while the corresponding formyl conformations are determined primarily by dipolar and electrostatic forces. No evidence for secondary stereoelectronic effects is apparent.     

A one-step conversion of esters to secondary alcohols with LiBH4-RMgX

A one-pot synthesis of secondary alcohols from esters and LiBH₄-RMgX is described.     

The mass spectra of the trimethylsilyl esters of acetyl,schiff base and isothiocyanate derivatives of some aminoalkylphosphonic acids

Trimethylsilyl esters of acetyl, Schiff base and isothiocyanate derivatives of a series of aminoalkylphosphonic acids were prepared for the purpose of characterizing these phosphorus compounds by combined gas chromatography and mass spectrometry. The mass spectra of these derivatives were investigated by means of high resolution mass measurments and deuterium labeling. Ions characteristic of the presence of the trimethylsilylphosnate group were observed at m/e 121, 195, 211 and 225 to 227 in the spectra of all the derivatives. Several ions produced by interaction between the trimethylsilyl group and the derivatized amino function were present, particularly in the spectra of the acetate derivatives ([M — 56]⁺, [M — R]⁺ and [M — 153]⁺, where R is the side chain attached to C-1), and the isothiocynate derivatives (m/e 268, 253, 241, 190 and 116).     

Palladium-catalyzed regiocontrolled alpha-arylation of trimethylsilyl enol ethers with aryl halides

Inter- and intramolecular arylations of trimethylsilyl enol ethers with aryl halides are accomplished regiospecifically in the presence of a palladium catalyst and tributyltin fluoride in refluxing benzene or toluene. The optimal catalyst system called for the use of Pd2(dba)3 and tri-tert-butylphosphine in ca. 1:2 ratio. Aryl iodides, bromides, and chlorides are all effective arylation partners in this reaction. [reaction: see text]     

Synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands

A simple and convenient procedure was developed for the synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands by condensation of 3,4-bis(2-iodoethoxy)benzaldehyde with ,-oligooxaalkanediamines or diazacrown ethers in the presence of alkali metal carbonates under high-dilution conditions in various organic solvents and their mixtures with water. In the reactions giving rise to diazacrown ethers, alkali metal cations exhibit the negative template effect resulting in a decrease in the yield of the target product if the size of the cation matches well the size of the cavity of the crown ether formed. An N,N"-bis(carboxymethyl) derivative was prepared from the formyl derivative of benzodiaza-18-crown-6.     

Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociations

Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH₂?C?O) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H₂CHO) and the acetyl radicals (CH₃C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (ΔH_f°₂₉₈) were determined using isodesmic reaction analysis at the CBS‐QCI/APNO and the CBSQ levels. Entropies (S°₂₉₈) and heat capacities (C_p°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6‐311G(d,p) level of theory. Internal rotor contributions were included in the S and C_p(T) values. A hydrogen atom can add to the CH₂‐group of the ketene to form the acetyl radical, CH₃C·O (E_a = 2.49 in CBS‐QCI/APNO, units: kcal/mol). The acetyl radical can undergo β‐scission back to reactants, CH₂?C?O + H (E_a = 45.97), isomerize via hydrogen shift (E_a = 46.35) to form the slight higher energy, formyl methyl radical, C·H₂CHO, or decompose to CH₃ + CO (E_a = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H₂CHO (E_a = 6.72). This formyl methyl radical can undergo β scission back to reactants, CH₂?C?O + H (E_a = 43.85), or isomerize via hydrogen shift (E_a = 40.00) to form the acetyl radical isomer, CH₃C·O, which can decompose to CH₃ + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice–Ramsperger–Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH₃ + CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH₂?C?O by H to form, ketenyl radical plus H₂ is identified with a barrier of 12.27, at the CBS‐QCI/APNO level. ΔH_f°₂₉₈ values are estimated for the following compounds at the CBS‐QCI/APNO level: CH₃C·O (?3.27), C·H₂CHO (3.08), CH₂?C?O (?11.89), HC·CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 20–44, 2003