The alkylation of alcohols and polyols has been investigated with alkylphosphates in the presence of a Lewis or Brønsted acid catalyst. The permethylation of polyols was developed under solvent‐free conditions at 100 °C with either iron triflate or Aquivion PW98, affording the isolated products in yields between 52 and 95 %. The methodology was also adjusted to carry out peralkylation with longer alkyl
Selective radical-chain epimerisation at electron-rich chiral tertiary C–H centres using thiols as protic polarity-reversal catalysts
作者:Hai-Shan Dang、Brian P. Roberts、Derek A. Tocher†
DOI:10.1039/b103558b
日期:——
Radical-chain epimerisation at chiral tertiary CH centres adjacent to ethereal oxygen atoms can be brought about in the presence of thiols, the function of which is to act as protic polarity-reversal catalysts for hydrogen-atom transfer between pairs of nucleophilic α-alkoxyalkyl radicals. The viability of the method is demonstrated by epimerisation of a series of simple molecules that contain two chiral centres and then the procedure is applied to more complex carbohydrate-based systems, where it is possible to convert a readily available diastereoisomer into a rarer one in a straightforward manner. Of necessity, epimerisation always proceeds in the direction of thermodynamic equilibrium and, in general, the results obtained are in accord with the predictions of molecular mechanics calculations using the MMX force-field. When the required isomer is less stable than the starting diastereoisomer, thiol-catalysed epimerisation of a suitable derivative of the parent can provide a means to obtain the desired compound in satisfactory yield, after deprotection of the epimerised derivative. This strategy is demonstrated for the conversion of trans-cyclohexane-1,2-diol into the less stable cis-isomer and for related contra-thermodynamic isomerisation of some carbohydrates, as well as for the conversion of meso-1,2-diphenylethane-1,2-diol into the dl-form. Thiol-catalysed epimerisation at a CH centre adjacent to an ether-oxygen atom is much faster than at a similar centre adjacent to an amido-nitrogen atom, a result that can be understood in terms of the importance of polar effects on the rate of abstraction of hydrogen by electrophilic thiyl radicals.
作者:Mattia Annatelli、Davide Dalla Torre、Manuele Musolino、Fabio Aricò
DOI:10.1039/d1cy00465d
日期:——
Dimethylisosorbide (DMI) is a well-known bio-based green replacement for conventional dipolar solvents such as dimethyl sulfoxide and dimethylformamide. The synthesis of DMI mainly relies on the etherification of the bio-based platform chemical isosorbide in the presence of basic or acid catalysts and by employing different alkylating agents. Among them, dimethyl carbonate (DMC) is considered one
Catalytic etherification of hydroxyl compounds to methyl ethers with 1,2-dimethoxyethane
作者:Penghua Che、Fang Lu、Xiaoqin Si、Jie Xu
DOI:10.1039/c4ra15919e
日期:——
1,2-Dimethoxyethane is explored as a new useful etherification agent for the 12-tungstophosphoric acid-catalyzed synthesis of methyl ethers from biomass-derived hydroxyl compounds.
Acid catalyzed synthesis of dimethyl isosorbide via dimethyl carbonate chemistry
作者:Davide Dalla Torre、Mattia Annatelli、Fabio Aricò
DOI:10.1016/j.cattod.2022.08.034
日期:2022.9
Dimethyl isosorbide (DMI) is a bio-based solvent that can be used as green alternative for conventional dipolar media (dimethyl sulfoxide, dimethylformamide, and dimethylacetamide). The main synthetic procedures to DMI reported in the literature are based on the methylation of isosorbide employing different alkylating agents including toxic halogen compounds such as alkyl halides. A more sustainable