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  • Inorganic Chemistry  (8)
  • Koenigs-Knorr reaction  (2)
  • Cyanohydrins  (1)
  • 1
    ISSN: 0170-2041
    Keywords: Glycosylation ; Koenigs-Knorr reaction ; Acyl-group migration ; Transesterification ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-O-[2,2,2-D3]Acetyl-3,4,6-tri-O-acetyl-α-D-galactopyranosyl bromide (3) was prepared and used as the glycosyl donor in studying the silver trifluoromethanesulfonate-promoted reaction with methyl 2,3,4-tri-O-benzoyl-β-D-galactopyranoside (4) and methyl 2,4,6-tri-O-benzoyl-β-D-galactopyranoside (7). In addition to the expected β-linked disaccharides, methyl 6-O-[2,2,2-D3]acetyl-2,3,4-tri-O-benzoyl-β-D-galactopyranoside (6) and methyl 3-O-[2,2,2-D3]acetyl-2,4,6-tri-O-benzoyl-β-D-galactopyranoside (9), respectively, were formed. The latter compounds were isolated from the reaction mixture and their structures were confirmed based on spectral data. Thus, it has been proven that, with fully acetylated glycosyl halides as glycosyl donors, in silver trifluoromethanesulfonate-promoted couplings, O-acetylation of the nucleophile occurs as a side reaction, the acetyl group involved originating from position 2 of the glycosyl halide.
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  • 2
    ISSN: 0170-2041
    Keywords: 2-Amino alcohols ; Cyanohydrins ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-Catalyzed Reactions, 8. - Stereoselective Synthesis of 2-Amino Alcohols from (R)- and (S)-Cyanohydrinserythro-2-Amino alcohols (1R,2S)- and (1S,2R)-4 may be synthesized stereoselectively by addition of Grignard compounds to cyanohydrins (R)-, (S)-1 and their O-trimethylsilyl derivatives 3, respectively, followed by hydrogenation. The threo-2-amino alcohols (1S,2S)- and (1R,2R)-4 are easily accessible by inversion at C-1 of the (1R,2S) and (1S,2R) compounds.
    Additional Material: 3 Tab.
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  • 3
    ISSN: 0170-2041
    Keywords: Glycosyl halides ; Haloacetates ; Koenigs-Knorr reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chloroacetylation of alkyl glycopyranosides of β-D-galactose, β-D-glucose and α-D-mannose as well as of free D-glucose, D-galactose, D-mannose and D-xylose, using chloroacetic anhydride as acylating reagent, gave the corresponding fully chloroacetylated pyranose derivatives in excellent yields. From D-glucose, 1,2,3,6-tetra-O-chloroacetyl-α-D-glucopyranose (9) was also obtained. Subsequent treatment of the fully chloroacetylated α-D-glycopyranoses 3, 8, 13 and 15 of galactose, glucose, mannose, and xylose, respectively, with HBr resulted in 2,3,4,6-tetra-O-chloroacetyl-α-D-galactopyranosyl bromide (4, 98%), -glucopyranosyl bromide (10, 92%), -mannopyranosyl bromide (14, 72%) and 2,3,4-tri-O-chloroacetyl-α-D-xylopyranosyl bromide (16, 68%). 10 reacted with D-pantholactone (17) and silver trifluoromethanesulfonate under acidic conditions to give the corresponding α-linked (18, 45%) and β-linked (20, 38%) glucopyranosides. Under basic conditions the corresponding ortho ester product 21 was formed (92%) which upon treatment with BF3 gave the glucosides 18 and 20. Silver silicate as the catalyst gave only traces of 18. Thus, 20 was isolated in 80% yield. Reaction of 10 with silver crotonate and silver laurate gave 1-O-crotonoyl- (22) and 1-O-lauroyl-2,3,4,6-tetra-O-chloroacetyl-β-D-glucopyranose (24), respectively. 18 and 22 were dechloroacetylated with thiourea, affording the corresponding deblocked glucose derivatives 19 and 23, respectively.
    Additional Material: 1 Tab.
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  • 4
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Enol Ethers, XVI. Synthesis of 4-Hydroxy-2H-pyran-2-onesEnol ethers 1 are acylated by malonyl dichlorides 2 to yield pentanoic acid derivatives 3; cyclisation of 3 with conc. sulfuric acid/10% SO3 results in the formation of 6-unsubstituted 4-hydroxy-2H-pyran-2-ones 4. The formation of pyrylium salts is decisive for the avoidance of side reactions. Spectroscopic investigations establish the structure of the compounds 4 as α-pyran-ones B.
    Notes: Enolether 1 werden mit Malonyldichloriden 2 zu Pentansäurederivaten 3 acyliert, deren Cyclisierung mit konz. Schwefelsäure/10% SO3 zu in 6-Stellung unsubstituierten 4-Hydroxy-2H-pyran-2-onen 4 führt. Die Bildung von Pyryliumsalzen ist entscheidend für die Vermeidung von Nebenreaktionen. Spektroskopische Untersuchungen beweisen das Vorliegen der Verbindungen 4 in der angegebenen α-Pyranon-Struktur B.
    Additional Material: 8 Tab.
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  • 5
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Enol Ethers, XVII. Acylation of Trimethylsilyl Enol Ethers with Malonyl Dichloride  -  Synthesis of 4-Hydroxy-2H-pyran-2-onesTrimethylsilyl enol ethers of aldehydes 1, acyclic and cyclic ketones 4 and 10, respectively, are acylated by malonyl dichloride (2) at room temperature or even at -60°C. After aqueous workup, the 6-unsubstituted 4-hydroxy-2H-pyran-2-ones 3 are obtained from 1-(trimethyl-siloxy)alkenes 1, whereas the 5,6-alkylene-bridged 4-hydroxy-2H-pyran-2-ones 11 are formed from 1-(trimethylsiloxy)cycloalkenes 10. Acylation of 2-(trimethylsiloxy)-1-propene (4a) and 3-(trimethylsiloxy)-2-pentene (4b) results in mixtures of 4-(trimethylsiloxy)-2H-pyran-2-ones 5 (main products) and phloroglucinol tris(trimethylsilyl) ethers 6 (by-products).
    Notes: (Trimethylsilyl)enolether von Aldehyden 1 und nichtcyclischen bzw. cyclischen Ketonen 4 bzw. 10 lassen sich mit Malonyldichlorid bei Raumtemperatur bzw. bereits bei -60°C acylieren. Hierbei entstehen nach wäßriger Aufarbeitung aus den 1-(Trimethylsiloxy)alkenen 1 die bislang nur schwer zugänglichen 6-unsubstituierten 4-Hydroxy-2H-pyran-2-one 3 und aus den 1-(Trimethylsiloxy)cycloalkenen 10 die 5,6-Alkylen-überbrückten 4-Hydroxy-2H-pyran-2-one 11. Die Acylierung von 2-(Trimethylsiloxy)-1-propen (4a) und 3-(Trimethyl-siloxy)-2-penten (4b) führt zu Gemischen aus 4-(Trimethylsiloxy)-2H-pyran-2-onen 5 (Hauptprodukte) und Phloroglucin-tris(trimethylsilylethern) 6 (Nebenprodukte).
    Additional Material: 2 Tab.
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  • 6
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diels-Alder Reactions with 2H-Pyran-2-ones: Reactivity and Selectivity2H-Pyran-2-ones 1 react with maleic anhydride (2) in a double Diels-Alder reaction to give bicyclo[2.2.2]oct-2-ene-5,6:7,8-tetracarboxylic dianhydrides 5; the syn/syn structure was established. As expected, the reactivity of 1 was increased by electron donor substituents (OR, alkyl) and diminished by electron withdrawing substituents (CO2R). The steric influence of substituents at C-6 also decrease the reactivity of 1. - Methyl propiolate (6) and phenylacetylene (9) react with 1 to form the Diels-Alder products 7 which suffer CO2 elimination to yield methyl benzoates 8 with low and biphenyls 10 with high regioselectivity, respectively.
    Notes: 2H-Pyran-2-one 1 gehen mit Maleinsäureanhydrid (2) eine zweifache Diels-Alder-Reaktion zu Bicyclo[2.2.2]oct-2-en-5,6:7,8-tetracarbonsäure-dianhydriden 5 ein, deren syn/syn-Struktur nachgewiesen wurde. Die Reaktivität von 1 wird erwartungsgemäß durch Donor-Substituenten (OR, Alkyl) erhöht und durch Acceptor-Substituenten (CO2R) verringert; Substituenten in 6-Stellung der α-Pyrone 1 führen infolge ihres sterischen Einflusses zu einer deutlichen Reaktivitätsverminderung. - Aus 1 und Propiolsäuremethylester (6) bzw. Phenylaceylen (9) entstehen über die primären Diels-Alder-Cycloadditionsprodukte 7 unter CO2-Abspaltung isomere Benzoesäure-methylester 8 mit geringer bzw. Biphenyle 10 mit hoher Regioselektivität.
    Additional Material: 11 Tab.
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  • 7
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Syntheses of Highly Substitued Benzenes via Diels-Alder Reactions with 2H-Pyran-2-onesThe 2H-pyran-2-ones (α-pyrones) 1 react as dienes in Diels-Alder reactions with acetylene derivatives. The primarely formed cycloadducts immediately aromatize to benzenes by CO2 elimination. Thus, methyl acetylenedicarboxylate (2a) gives dimethylphthalates 3, and methyl acetylenediphosphonate (2b) gives dimethyl 1,2-phenylenediphosphonates 8. The reactions of 1-(dimethylamino)-1-methoxyethene (9) with 1 regioselectively produce N,N-dimethylanilines 10 and isomeric homophthalate derivatives 12. Naphthoquinones 14 could be generated from 1,4-benzoquinone (13) and 1 in the presence of acetic anhydride and Pd/C. Hydroxy-2H-pyran-2-ones 4 react via their trimethylsilyl ether 6 analogously with 2a to give dimethyl (trimethylsiloxy)-phthalates 7 which are easily converted to phenols 5 by acidcatalyzed hydrolysis.
    Notes: Acetylenderivate reagieren mit 2H-Pyran-2-onen (α-Pyronen) 1 als Dien-Komponenten primär zu Diels-Alder-Cycloadditionsprodukten, die sofort unter CO2-Abspaltung zu Benzolderivaten aromatisieren. So werden mit Acetylendicarbonsäure-dimethylester (2a) Phthalsäure-dimethylester 3 und mit Acetylenbis(phosphonsäure-dimethylester) (2b) 1,2-Phenylenbis(phosphonsäure-dimethylester) 8 erhalten. 1-(Dimethylamino)-1-methoxyethen (9) sowie 2,3-Pentadiendisäure-dimethylester (11) bilden mit 1 regioselektiv N,N-Dimethylaniline 10 sowie isomere Homophthalsäure-Derivate 12. Aus 1,4-Benzochinon (13) und 1 entstehen in Gegenwart von Acetanhydrid und Pd/C Naphthochinone 14. Hydroxy-2H-pyran-2-one 4 lassen sich über ihre Trimethylsilylether 6 mit 2a zu den (Trimethylsiloxy)phthalsäure-dimethylestern 7 umsetzen, deren säurekatalysierte Hydrolyse glatt zu den Phenolen 5 führt.
    Additional Material: 13 Tab.
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  • 8
    ISSN: 0009-2940
    Keywords: (R)-2-Hydroxy aldehydes, O-protected ; Hydrocyanation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of O-Protected (R)-2-Hydroxy Aldehydes and Their HydrocyanationThe synthesis of O-silyl- and O-benzyl-protected (R)-2-hydroxy aldehydes (R)-6 from (R)-2-hydroxy carboxylic acids (R)-1 is described. While attempts for their diastereoselective hydrocyanation with hydrocyanic acid and (R)-oxynitrilase as catalyst have not been successful, the cyano silylation with trimethylsilyl cyanide occurred diastereoselectively with a ratio of 81 : 19 preferring the threo form without racemization at C-2 of the 2-hydroxy aldehyde.
    Additional Material: 6 Tab.
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  • 9
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: In boiling 1,2-dichloroethane 3-ethoxyacryloyl chloride (1) reacts with phenols 2 to yield 3-ethoxyacrylates 3, which by treatment with conc. sulfuric acid/10% SO3 cyclize to give coumarins 9 in good yields. The methoxy-substituted compounds 3d and 3k do not react to coumarins 9 with H2SO4/SO3 but with POCl3/H2O at room temperature.
    Notes: Aus 3-Ethoxyacryloylchlorid (1) und Phenolen 2 entstehen in siedendem 1,2-Dichlorethan 3-Ethoxyacrylsäure-arylester 3, die sich mit konz. H2SO4/10% SO3 bei 0°C in guten Ausbeuten zu Cumarinen 9 cyclisieren lassen. Die 3-Ethoxyacrylsäure-methoxy-phenylester 3d und 3k cyclisieren unter diesen Bedingungen nicht, lassen sich jedoch mit POCl3/H2O bei Raumtemperatur ebenfalls in guten Ausbeuten in die entsprechenden Cumarine 9d und 9k überführen.
    Additional Material: 5 Tab.
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  • 10
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Enol Ethers, XIII. Acylation of Enol Ethers with Reactive Carbonyl ChloridesEnol ethers 2 are acylated under mild conditions with activated acyl chlorides, e.g. chloroacetyl chlorides 1a, b, cyanoacetyl chloride (6c), and malonic acid chlorides 6a,b in good yields. The products formed and the yield depend on the acylation potential of the acyl chlorides. The potential β-keto aldehydes 4, 5, and 1,3,5-tricarbonyl compounds 8 obtained are valuable intermediates for heterocyclic synthesis.
    Notes: Enolether 2 lassen sich mit aktivierten Säurechloriden wie den Chloressigsäurechloriden 1a und 1b, Cyanacetylchlorid (6c) oder Malonylchloriden 6a, b unter milden Bedingungen in guten Ausbeuten acylieren. Die Abhängigkeit der Produktbildung und der Ausbeuten vom Acylierungspotential der eingesetzten Säurechloride wird aufgezeigt. Die erhaltenen potentiellen β-Ketoaldehyde 4, 5 bzw. 1,3,5-Tricarbonylverbindungen 8 sind wertvolle Zwischenprodukte für die Synthese von Heterocyclen.
    Additional Material: 6 Tab.
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