- Hydrogen Rearrangements in Alkyl-, Styryl- and Alkyl Propenyl Sulfoxides
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The McLafferty-type rearrangements, which are the most facile fragmentation for the styryl- and the alkyl propenyl sulfoxides, have been proven to involve at least a β-hydrogen by deuterium labelling studies. γ-Hydrogen also rearranges, yet a cyclopropane instead of an alkene is eliminated.Furthermore, alkyl propenyl sulfoxides undergo hydrogen migration only to the sulfinyl oxygen.
- Liu, Lilian Kao,Su, C. Y.,Li, Wen-Shan
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- A simple preparation of hexadeuteriocholesterol
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26,26,26,27,27,27 Hexadeuterio cholesterol has been prepared in 9 steps from pregnenolone and hexadeuterio acetone with an overall yield of 7%.
- Holm, Torkil,Crossland, Ingolf
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- A stable isotope labeled 2 - isopropyl thioxanthone and its synthesis method
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The invention relates to stable isotopic labeled 2-isopropylthioxanthone and a synthetic method thereof. The stable isotopic labeled 2-isopropylthioxanthone is 2-isopropylthioxanthone labeled by D or 13C. The synthetic method comprises the following steps of using benzene and acetone which are labeled by stable isotopic D or 13C as raw materials; reacting the benzene and the acetone with magnesium to obtain Grignard reagent after benzene bromination; performing reduction and hydroxide radical bromination on the acetone to obtain 2-bromic propane; performing Grignard reaction to obtain isopropyl benzene; reacting the isopropyl benzene with dithio-salicylic acid; and synthesizing to obtain the 2-isopropylthioxanthone labeled by the stable isotopic D or 13C. Compared with the prior art, the stable isotopic labeled 2-isopropylthioxanthone has the advantages that a process route is simple, the 2-isopropylthioxanthone is easy to synthesize, products are easy to separate and purify, the chemical purity of the products is above 99.0%, isotope abundance is above 98.0% atom, requirements of trace detection in the field of food safety can be met fully, and economical efficiency and using value are excellent.
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Paragraph 0053; 0098-0099; 0108-0109; 0118-0119; 0202
(2018/04/21)
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- Efficient synthesis of D6-clenproperol and D6-cimaterol using deuterium isopropylamine as labelled precursor
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This report presents an efficient synthesis of D6-clenproperol and D6-cimaterol with 99.5% and 99.7% isotopic abundance in acceptable yields and excellent chemical purities with deuterium isopropylamine as labelled precursor. Their structures and the isotope-abundance were confirmed by proton nuclear magnetic resonance and liquid chromatography–mass spectrometry.
- Sun, Kai,Fang, Chao,Yang, Weicheng,Xu, Zhongjie,Wang, Haoran,Sun, Wen,Luo, Yong,Xu, Yi
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p. 552 - 556
(2016/11/23)
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- Synthesis of isotopically labelled 2-isopropylthioxanthone from 2,2′-dithiosalicylic acid and deuterium cumene
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Two efficient synthetic routes of stable deuterium labelled 2-isopropylthioxanthone were presented with 98.1% and 98.8% isotopic abundance in acceptable yields and excellent chemical purities. Their structures and the isotope-abundance were confirmed according to proton nuclear magnetic resonance and liquid chromatography–mass spectrometry.
- Fang, Chao,Yang, Weicheng,Yang, Chao,Wang, Haoran,Sun, Kai,Luo, Yong
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p. 313 - 316
(2016/07/11)
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- Hydrodehalogenation of 1,1-dibromocyclopropanes by Grignard reagents promoted by titanium compounds
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1,1-Dibromocyclopropanes are converted into the corresponding monobromocyclopropanes (as mixtures of stereoisomers where appropriate) by reaction with 1.0-1.3 mol equiv. of ethylmagnesium bromide and 2-10 mol% titanium isopropoxide for 90%). With ethylmagnesium bromide, the reaction occurs very slowly in the absence of catalyst; with methylmagnesium bromide, the reaction does occur in the absence of catalyst, but is only slightly promoted in the presence of titanium isopropoxide. Reactions with a number of other Grignard reagents are also discussed. In the case of phenethylmagnesium bromide, the major product containing the phenethyl-group is ethylbenzene, together with small amounts of styrene and ethyl 4-phenyl-2-butyl ether, a product of trapping of the solvent, ether. In other cases, relatively large amounts of a diether, formally derived by hydrogen ion adjacent to the ether oxygen followed by dimerisation, are isolated. No products were identified incorporating the cyclopropane and either the Grignard alkyl group or the solvent. Labelling studies indicate that the hydrogen introduced into the cyclopropane is not derived from either the α- or β-positions of the Grignard reagent. When the reduction is carried out with phenethylmagnesium bromide in d8-tetrahydrofuran both monobromides contain deuterium.
- Dulayymi, Juma'a R. Al,Baird, Mark S.,Bolesov, Ivan G.,Nizovtsev, Alexey V.,Tverezovsky, Viacheslav V.
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p. 1603 - 1618
(2007/10/03)
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- Intermediacy of ion neutral complexes in the fragmentation of short-chain dialkyl sulfides
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The main fragmentation processes after electron ionization of butyl methyl and butyl ethyl sulfides are rationalized by the intermediacy of the ion neutral complex [RSH · methylcyclopropane](+·) as demonstrated by extensive labeling and collision activation studies.
- Filsak,Budzikiewicz
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p. 601 - 610
(2007/10/03)
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- The enzymatic synthesis of isotopically labelled penicillin Ns with isopenicillin N synthase
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The preparation of isotopically labelled penicillin Ns using a chemico-enzymatic approach is described. This route involves the chemical synthesis of variously labelled D,L,D,-aminoadipoyl-cysteinyl-valine tripeptides via well established facile protocols and concludes with the conversion of these tripeptides directly into penicillin Ns by the action of recombinant isopenicillin N synthase. Milligram quantities of isotopically labelled penicillin Ns, which would otherwise represent very challenging and expensive synthetic targets, are readily accessible from this route.
- Baldwin, Jack E.,Adlington, Robert M.,Crouch, Nicholas P.,Pereira, Ines A.C.
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p. 1145 - 1163
(2007/10/03)
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- Regiospecificity and Isotope Effects Associated with the Methyl-Methylene Eliminations in the Enzyme-Catalyzed Biosynthesis of (R)- and (S)-Limonene
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-, -, and geranyldiphosphates (1-t, 1-d4, and 1-d6,t) were synthesized and used as substrates for several monoterpene cyclases to determine the regiospecificity and isotope effects attending the terminating proton transfers in the enzyme-catalyzed biosynthesis of (R)- and (S)-limonene.Degradation of enantiomeric limonenes produced by cyclization of 1-t with the (+)- and (-)-pinene cyclases (synthases) from Salvia officinalis demonstrated that the eliminations occur at both the cis- (55-65percent) and trans-methyl (45-35percent) groups.In contrast, the terminating eliminations in the formation of (+)- and (-)-limonene catalyzed by limonene cyclases from Citrus sinensis and Perilla frutescens, respectively, were shown by degradation to occur exclusively (>/=97-98percent) at the cis terminal methyl group.The intramolecular isotope effects for the methyl-methylene elimination in limonene biosynthesis catalyzed by (+)- and (-)-pinene cyclases from S. officinalis were found to be kH/kD = 2.3 +/- 0.2 and 5.9 +/- 0.5, respectively, by GC/MS determinations of -limonene derived from enzymatic cyclizations of 1-d4.Similar experiments with (-)-limonene cyclase from Mentha spicata resulted in kH/kD = 4.0 +/- 0.4.Incubations of 1-d6,t with pinene and bornyl PP cyclases from S. officinalis exhibited significant remote isotope effects (kH/kD = 1.16-1.27) on the total rate of monoterpene formation which suggest that the initial cyclization step of the enzyme-bound linalyl diphosphate intermediate is an important component of the overall rate of the enzymatic reactions.The isotope effects on the partitioning of the α-terpinyl carbocation intermediate between bicyclization and elimination to limonene were determined from the effects of deuterium substitution on the product ratios derived from enzymatic cyclization of 1-d6,t.The small size of these product isotope effects (kH/kD = 1.2-1.7) is attributed to a conformational inversion of the α-terpinyl ion to a half-chair conformer prior to proton elimination to limonene, thereby rendering the bicyclizations relatively immune to the intrinsic deuterium isotope effect.The regiospecific proton transfers from the cis terminal methyl group effected by the limonene cyclases from Citrus and Perilla are attributed to the minimization of charge seperation in the transition state.
- Pyun, Hyung-Jung,Coates, Robert M.,Wagschal, Kurt C.,McGeady, Paul,Croteau, Rodney B.
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p. 3998 - 4009
(2007/10/02)
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- Tobacco Smoke Chemistry. 4. A Mass Spectral Study of Alkyl 3-Hydroxy-4-pyrones
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3-Hydroxy-4-pyrone and a series of C-alkylated 3-hydroxy-4-pyrones have been synthesized and their behaviour under electron impact investigated.The fragmentation pathways were elucidated with the aid of accurate mass measurements, metastable ion analysis and deuterium labelling.All compounds examined gave a detectable molecular ion which undergoes a retro Diels-Alder type process accompanied by hydrogen transfer to give characteristic ions, which in many cases allow differentiation of positional isomers.Loss of carbon monoxide is encountered from several ions, but to any substantial extent from the molecular ions only in the cases of 3-hydroxy-4-pyrone and 5-hydroxy-2-methyl-4-pyrone.Instead, the more general fragmentation routes involve extrusion of a hydrogen or an alkyl radical from the molecular ion prior to the elimination of carbon monoxide.When the alkyl substituent in 2-alkyl-3-hydroxy- or 2-alkyl-5-hydroxy-4-pyrone has three or more consecutive carbons the molecular ion loses an alkene fragment by a McLafferty type of reaction.The even mass ions formed by this process constitute the base peak in most spectra of this type.Another rearrangement reaction giving even mass ions after loss of an alkene fragment, occurs when the alkyl substituent in the 2-alkyl-3-hydroxy-4-pyrones is branched at the α-carbon.Moreover, γ-bond cleavage of the alkyl side chain vicinal to the hydroxy group becomes important due to anchimeric assistance by the hydroxy group.
- Arnarp, Jan,Bielawski, Jacek,Dahlin, Britt-Marie,Dahlman, Olof,Enzell, Curt R.,Pettersson, Tore
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p. 916 - 926
(2007/10/02)
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- Thermal rearrangements of allenes. Synthesis and mechanism of cycloaromatization of π and heteroatom bridged diallenes
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The synthesis and thermal rearrangement of several π and heteroatom bridged diallenes has been investigated. o-Diallenylbenzenes 5, 14, 24 and bis(γ,γ-dimethylallenyl) ether 8 were prepared by addition of dibromocarbene to the corresponding divinyl precursor, followed by treatment of the resulting dibromocyclopropane derivative with methyllithium. Bis(γ,γ-dimethylallenyl) sulfide 10 was generated by reaction of (γ,γ-dimethylallenyl)lithium with sulfur dichloride, while the corresponding selenides 12 and 16 were synthesized by an SN2′ reaction of sodium selenide with α,α-dimethylpropargyl bromide. All diallenes prepared display a remarkable thermal reactivity and undergo a facile cycloaromatization. Gentle heating of diallenes 5, 14, 12, and 16 gave the naphthalene derivatives 6 and 15 and selenophene derivatives 13 and 17, respectively, in practically quantitative yields. Diallenes 8, 10, and 24 underwent spontaneous cyclization during preparation yielding furan 9, thiophene 11, and naphtho[b]cyclobutane 25, respectively. A kinetic study of the rearrangement and measurement of the kinetic isotope effect using diallenes 5, 14, 12, and 16, revealed that the cyclization is a two-step process. The first and rate-determining step is an electrocyclic reaction yielding as intermediates ω-xylylenes 20 and 21, while the second and more rapid step entails a [1,5]hydrogen transfer.
- Braverman, Samuel,Duar, Ytzhak
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p. 5830 - 5837
(2007/10/02)
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