- Dehydroxymethylation of alcohols enabled by cerium photocatalysis
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Dehydroxymethylation, the direct conversion of alcohol feedstocks as alkyl synthons containing one less carbon atom, is an unconventional and underexplored strategy to exploit the ubiquity and robustness of alcohol materials. Under mild and redox-neutral reaction conditions, utilizing inexpensive cerium catalyst, the photocatalytic dehydroxymethylation platform has been furnished. Enabled by ligand-to-metal charge transfer catalysis, an alcohol functionality has been reliably transferred into nucleophilic radicals with the loss of one molecule of formaldehyde. Intriguingly, we found that the dehydroxymethylation process can be significantly promoted by the cerium catalyst, and the stabilization effect of the fragmented radicals also plays a significant role. This operationally simple protocol has enabled the direct utilization of primary alcohols as unconventional alkyl nucleophiles for radical-mediated 1,4-conjugate additions with Michael acceptors. A broad range of alcohols, from simple ethanol to complex nucleosides and steroids, have been successfully applied to this fragment coupling transformation. Furthermore, the modularity of this catalytic system has been demonstrated in diversified radical-mediated transformations including hydrogenation, amination, alkenylation, and oxidation.
- Zhang, Kaining,Chang, Liang,An, Qing,Wang, Xin,Zuo, Zhiwei
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supporting information
p. 10556 - 10564
(2019/08/20)
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- Dehydroxymethylation of Alcohols Enabled by Cerium Photocatalysis
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Dehydroxymethylation, the direct conversion of alcohol feedstocks as alkyl synthons containing one less carbon atom, is an unconventional and underexplored strategy to exploit the ubiquity and robustness of alcohol materials. Under mild and redox-neutral reaction conditions, utilizing inexpensive cerium catalyst, the photocatalytic dehydroxymethylation platform has been furnished. Enabled by ligand-to-metal charge transfer catalysis, an alcohol functionality has been reliably transferred into nucleophilic radicals with the loss of one molecule of formaldehyde. Intriguingly, we found that the dehydroxymethylation process can be significantly promoted by the cerium catalyst, and the stabilization effect of the fragmented radicals also plays a significant role. This operationally simple protocol has enabled the direct utilization of primary alcohols as unconventional alkyl nucleophiles for radical-mediated 1,4-conjugate additions with Michael acceptors. A broad range of alcohols, from simple ethanol to complex nucleosides and steroids, have been successfully applied to this fragment coupling transformation. Furthermore, the modularity of this catalytic system has been demonstrated in diversified radical-mediated transformations including hydrogenation, amination, alkenylation, and oxidation.
- Zhang, Kaining,Chang, Liang,An, Qing,Wang, Xin,Zuo, Zhiwei
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supporting information
p. 10556 - 10564
(2019/08/28)
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- Asymmetric conjugate addition to alkylidene malonates
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Dialkylzinc and trialkylaluminium reagents undergo conjugate addition to alkylidene malonates with 0.5% copper triflate as catalyst. The reaction could be made enantioselective by completing the reaction in the presence of 0.5-1.0 mol% of chiral phosphorus ligand. Enantiomeric excesses (e.e.s) of up to 73% could be attained with a ligand prepared from TADDOL and 2-naphthylcyclohexanol.
- Alexakis, Alexandre,Benhaim, Cyril
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p. 1151 - 1157
(2007/10/03)
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- Mixed Dialkylaluminum Chlorides and Mixed Trimethylorganoaluminates in Chemoselective 1,4 Addition Reactions to Alkylidene Malonic Acid Diethyl Ester
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Mixed alkyl-methyl- and aryl-methylorganoaluminum chlorides 6 were formed by reaction of methylaluminum dichloride with organolithium or Grignard compounds and used for chemoselective 1,4 addition of higher alkyl, aryl, alkenyl and alkinyl groups to alkylidine malonic esters 1 and 2. As an alternative, mixed trimethylorganoaluminates 7 can also be applied for these Michael addition reactions. For conjugate addition of alkenyl groups to alkylidene malonates 1 and 2, alkenyl diisopropylalanes 10 obtained from alkynes and diisopropylaluminum hydride proved the most efficient reagents. Using these novel mixed organoaluminum compounds, β-branched malonic (carboxylic) acid derivatives 3c, 8, 9 and 11 were obtained in good yields. The method offers a general access to β-branched carboxylic derivatives of quite diverse structure not dependent on the commercial availability of the organoluminum chlorides.
- Maas, Steffen,Kunz, Horst
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p. 396 - 403
(2007/10/03)
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- Conjugate addition of dialkylaluminum chlorides to alkylidenemalonic acid derivatives
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Complete regioselectivity is achieved in conjugate addition reactions of dialkylaluminum chlorides with alkylidenemalonic esters, alkylidenecyanoacetates, and alkylidenemalonodinitrile to give β-branched carboxylic acid derivatives. Sterically demanding products containing quaternary carbon atoms are obtained in good yields. In the case of diethylaluminum chloride, accompanying reductions of the substrates can be suppressed by application of boron trifluoride as an assisting Lewis acid.
- Maas, Steffen,Stamm, Armin,Kunz, Horst
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p. 1792 - 1798
(2007/10/03)
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- Acceleration of the conjugate addition of diethyl zinc to enones by either Cu(OTf)2 or trivalent phosphorus ligands
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The conjugate addition of diethyl zinc to enones under copper catalysis occurs well with copper (II) trifiate. Other copper salts need a phosphine or phosphite ligand to be efficient. The best combination is copper (II) triflate and triethyl phosphite. A very small amount of copper (II) triflate (0.5%) and triehtyl phosphite (1%) are enough for high yields.
- Alexakis,Vastra,Mangeney
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p. 7745 - 7748
(2007/10/03)
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- 170. Asymmetric Palladium-Assisted Alkylation of Alkenes
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Palladium-promoted alkylation of alkenes using chiral sulfoxide-containing carbanions and chiral lithiated oxazolines results in asymmetric induction (AI) ranging from 3-5 percent (1,5 induction), 20-40 percent (1,3 induction) to 44-52 percent (1,4 induction).No general trend allowing predictions of results was found.With 1-hexene, attack at C(1) is almost exclusive but propene gives a mixture of attack at C(1) and C(2).The use of a chiral ligand together with malonate anion also leads to some asymmetric induction (ca. 20 percent).
- Solladie-Cavallo, Arlette,Haesslein, Jean-Luc
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p. 1760 - 1773
(2007/10/02)
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- ASYMMETRIC PALLADIUM-ASSISTED ALKYLATION OF OLEFINS
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Palladium-promoted alkylation of some alkenes using chiral sulfoxide-containing carbanion as nucleophiles or using optically active N,N-dimethyl-α-phenylethylamine as ligand together with a non-chiral stabilized carbanion as nucleophile results in an asymmetric induction of 10-40percent.
- Solladie-Cavallo, A.,Haesslein, J. L.,Baeckvall, Jan-E.
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p. 939 - 942
(2007/10/02)
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