Singlet oxygen oxidation of substituted furans to 5-hydroxy-2(5H)-furanone
摘要:
The conditions for the regiospecific singlet oxygen oxidation of various 2,4-disubstituted furans 9 to 4-substituted-2 (5H)-furanones 3 are developed. The presence of a C-2 substituent (e.g., trimethylsilyl, tert-butyldimethylsilyl, or tributylstannyl) in 9 is an absolute requirement for the formation of the 4-substituted-5-hydroxy-2(5H)-furanone regioisomer 3. When the C-2 substituent is triethylsilyl (TES) or TBDMS, however, apart from 3, the corresponding 5-trialkylsiloxy derivative 11 is also isolated in a significant amount. These silyl acetals are unexpectedly stable but can be hydrolyzed back to 3 on stirring with dilute acid. The formation of silyl acetals, to our knowledge, has never been reported in the singlet oxygen oxidation of (trialkylsilyl)furan. A plausible mechanism for their formation is proposed. The presence of a catalytic amount of water in the oxidation of 2-(trialkylsilyl)-4-substituted-furans not only eliminates the formation of the silyl acetals but also speeds up the rate of the oxidation process. Moreover, the oxidation can then be carried out at 0-degrees-C instead of at -78-degrees-C. Oxidation of 2-(1-hydroxyalkyl)-4-substituted-furans in the absence of a reducing agent gives little or no sign of 2,5-disubstituted-6-hydroxy-3(2H)-pyranone 23 but instead 26 selectively. Thus, the (1-hydroxy)alkyl group can be utilized as the trialkylsilyl or trialkylstannyl group in dictating the regioselectivity in the singlet oxygen oxidation of substituted furans.
Organoceriumreagents, prepared in situ by the treatment of organolithium compounds with cerium(III) iodide, exhibit characteristic reactivities toward ketones; at –65 °C, nucleophilic additions give the corresponding tertiary alcohols in excellent yields, while, at 0 °C to ca. room temperature, reductive coupling and/or reduction of the ketones prevail.
catalytic methods for the oxidative furan-recyclizations remain scarcely investigated. Given this, we report a means of manganese-catalyzed oxidations of furan with low loading, achieving the Achmatowiczrearrangement in the presence of hydrogen peroxide as an environmentally benign oxidant under mild conditions with wide functional group compatibility.
Tandem Catalysis: Alcohol Oxidation and CC Bond Formation via CH Bond Activation
作者:Marc-Olivier Simon、Gaël Ung、Sylvain Darses
DOI:10.1002/adsc.201000884
日期:2011.5.9
A tandem process involving oxidation of a benzylicalcohol functionality followed by hydroarylation is described. These two atom‐economic sequences are very convenient to access functionalized aromatic ketones, using simple ruthenium trichloride as catalyst precursor. Moreover they appear to be highly compatible, tolerant, and selective toward various functional groups, and the ease of the protocol
作者:Daniel Thiel、Fabian Blume、Christina Jäger、Jan Deska
DOI:10.1002/ejoc.201800333
日期:2018.6.7
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Structure–Odor Correlations in Homologous Series of Mercapto Furans and Mercapto Thiophenes Synthesized by Changing the Structural Motifs of the Key Coffee Odorant Furan-2-ylmethanethiol
作者:Sebastian Schoenauer、Peter Schieberle
DOI:10.1021/acs.jafc.8b00857
日期:2018.4.25
seeds. Its unique coffee-like odor quality elicited at very low concentrations, and the fact that only a very few compounds showing a similar structure have previously been described in foods make 1 a suitable candidate for structure–odor activity studies. To gain insight into the structural features needed to evoke a coffee-like odor at low concentrations, 46 heterocyclic mercaptans and thio ethers