- Impregnated palladium on magnetite as a water compatible catalyst for the cycloisomerization of alkynoic acid derivatives
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This work describes the catalytic activity of palladium(ii) species in the cycloisomerization of alkynoic acids and their derivatives in aqueous media as well as in Deep Eutectic Solvents (DESs), with one of the lowest metal catalyst loadings reported so far in the literature. Different substrates such as terminal and internal alkynes or alkynyl sulfonylimides were studied, obtaining selectivity either to the cyclic compound or the hydrolysed keto derivative. This new system avoids the use of harmful solvents and employs very efficient and recoverable heterogeneous catalysts.
- Saavedra, Beatriz,Pérez, Juana M.,Rodríguez-álvarez, María J.,García-álvarez, Joaquín,Ramón, Diego J.
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p. 2151 - 2157
(2018/05/23)
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- Decomposition du percarbonate de O,O-t-butyle et O-isopropenyle en solution: acetonylation des esters, acides et nitriles
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The free-radical decomposition of O,O-t-butyl and O-isopropenyl peroxycarbonate in substrates possessing mobile H-atoms (S-H) consists mainly in an induced chain process leading to acetonylated derivatives of the solvent.Fairly good yields are obtained but the acetonylation of functional substrates often gives mixtures of isomers.In the case of methyl acetate, the acetonylation occurs on the C-atoms adjacent to the carbonyl (acyloxy moiety) and to the O-atom (alkoxy moiety).However, the relative amounts of the isomeric products depend on the concentration of the peroxycarbonate solutions; at lowest concentration, methyl 4-oxopentanoate (acyloxy moiety) is obtained selectively.It is assumed that the free radicals issued from the solvent are able to abstract H-atoms of other molecules of solvent before adding to the double bond of the peroxycarbonate; the more the peroxycarbonate solution is diluted the more the transfers from the C-atom adjacent to the carbonyl to the radicals adjacent to the O-atom are favoured.In the case of methyl alkanoates, H-transfers from the α-C-atoms to β-radicals of the acyloxy moiety may account for the orientation of the process.Owing to similar H-transfer processes, the acetonylation of functional esters, of acids and nitriles is selective in most cases.
- Lalande, Robert,Filliatre, Claude,Villenave, Jean-Jacques,Jaouhari, Rabih
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p. 149 - 159
(2007/10/02)
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