- Reactivity of benzylidene and alkylidenemalonates in radical addition mediated with dialkylzincs – An intriguing story
-
Benzylidene- and alkylidenemalonates are extremely reactive radical acceptors in dialkylzinc-mediated radical additions. Theoretical investigations showed that the multi-step radical-polar crossover process should be highly exothermic. Not only the addition of the alkyl radical to the complexed substrate is enthalpically favored but what is more, the homolytic substitution at the metal leading to a zinc enolate should also be exothermic, even though it necessitates the cleavage of the C-Zn bond from the complexed α-alkoxycarbonyl radical intermediate. This work was undertaken to highlight the power of chelation in controlling the fate of this type of reaction. Much to our surprise, no unambiguous experimental evidence could be put forward to prove the formation of the expected zinc enolate intermediate. Additionally, benzylidenemalonates and their alkylidene analogues (although to a lesser extent) exhibit an intriguing behavior. The backward reaction (retro-addition) can be triggered at work-up depending upon experimental conditions.
- Lingua, Hugo,Dwadnia, Nejib,Siri, Didier,Bertrand, Michèle P.,Feray, Laurence
-
-
Read Online
- Preparation method and application of chiral spiro aminophosphine ligand with substituent at 3-position of pyridine ring
-
The invention relates to a preparation method and application of a chiral spiro aminophosphine ligand with a substituent at the 3-position of a pyridine ring. The chiral spiro aminophosphine ligand isa compound shown as a formula 1, or a racemate or an op
- -
-
Paragraph 0057-0060; 0063
(2020/02/14)
-
- Asymmetric conjugate addition to alkylidene malonates
-
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
-
p. 1151 - 1157
(2007/10/03)
-
- Conjugate addition of dialkylaluminum chlorides to alkylidenemalonic acid derivatives
-
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
-
p. 1792 - 1798
(2007/10/03)
-
- Stereocontrol in the intramolecular Buchner reaction of diazoketones
-
Rhodium(II) acetate catalysed intramolecular Buchner cyclisation of a series of diazoketones 1 proceeds with excellent diastereoselectivity to produce the trans substituted azulenones 2, which exist as a rapidly equilibrating cycloheptatriene-norcaradiene system, from which the norcaradiene tautomers can be efficiently trapped as PTAD cycloadducts 4. The cyclisation-cycloaddition sequence can be conducted in either a stepwise or a tandem process, leading to the pentacyclic systems 4 as a single diastereomer in each case. In the reaction of diazoketone If intramolecular cyclopropanation competes with cyclisation to the aromatic ring.
- Maguire, Anita R.,Buckley, N. Rachael,O'Leary, Patrick,Ferguson, George
-
p. 4077 - 4091
(2007/10/03)
-
- Synthesis of 3-Phenoxybenzyl 3-Alkyl-3-phenyl-/p-substituted phenyl and 3-Phenoxybenzyl 2-Alkyl-3-phenyl-/p-substituted phenylpropionates
-
Some 3-phenoxybenzyl 3-alkyl-3-phenyl-/p-substituted phenylpropionates (VII, XI, XV, XIX, XXIII, XXVII) which resemble structurally the 1,2-secopyrethroids, have been prepared employing simple reactions like alkylation, decarbethoxylation and transesterification.The synthesis of 3-phenoxybenzyl 2-alkyl-3-phenyl-/p-substituted phenyl-propionates (XXXI, XXXII, XXXIII, and XXXVI) bearing close structural resemblance to 2,3-secopyrethroids has also been described.
- Kelkar, S. V.,Joshi, G. S.,Kulkarni, G. H.,Mitra, R. B.
-
-
- 170. Asymmetric Palladium-Assisted Alkylation of Alkenes
-
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
-
p. 1760 - 1773
(2007/10/02)
-
- ASYMMETRIC PALLADIUM-ASSISTED ALKYLATION OF OLEFINS
-
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.
-
p. 939 - 942
(2007/10/02)
-