Copper-free asymmetric allylic alkylation with grignard reagents
(Chemical Equation Presented) Open wide and say AAA: The copper-free asymmetric allylic alkylation reaction of Crignard reagents, catalyzed by N-heter-ocyclic carbenes, is reported for allyl bromide derivatives. This reaction offers good enantioselectivit
Jackowski, Olivier,Alexakis, Alexandre
supporting information; experimental part
p. 3346 - 3350
(2010/07/15)
Novel ortho-Alkoxy-Substituted Phosphorus Ylides and Their Stereoselectivity in Wittig Reactions
The stereochemistry of the reactions between tris(2-methoxymethoxypheny)phosphonioethanide (1f), -butanide (2f), and -phenyl-methanide (3f) and a variety of aldehydes was investigated.Ylides having a β-unbranched aliphatic sidechain, such as 2f, and saturated straight-chain aldehydes give olefins with unprecedented cis-selectivity (cis/trans ca. 200:1).
Untersuchungen im Wittig-System nach einem ordnenden Konzept auf der Basis alternativer Prinzipien
Our results show that the stereoselectivity of the Wittig-reaction can be controlled by the variation of substituents in accord with the ORDERING CONCEPT OF ALTERNATIV PRINCIPLES (individual pairs, known and unknown classes of alternatives).The "all-phenyl Wittig-system" having three phenyl groups on phosphorous two in ylid- and aldehyd-position was chosen as a standard for our investigations.Differentiation in ylid-position and compensation on phosphorous and aldehyd-position were observed by the comparison of "patterns".Consequently, most of the selectivity rules of Wittig-reactions can be explained by the differentiation through alternatives in the ylid-position.Inversion or conservation of the "patterns" of measured data points to the variation in structure of starting materials, reaction rates and selectivities.Amount-controls were also described in certain systems.
NMR RATE ON THE WITTIG REACTION OF 2,2-DIMETHYLPROPANAL AND TRIBUTYLBUTYLIDENEPHOSPHORANE
The fate of intermediate oxaphosphetanes in the reaction of t-BuCHO and Bu3P=CHPr was monitored with time.Cis oxaphosphetane 1a was converted to trans oxaphosphetane 1b at -55 deg C with k3=1.5E-4 s-1, and 1b was converted to Bu3P=O and alkene 2b at -15 deg C with k6=2.7E-5 s-1 (t1/2=7.0 h).
Maryanoff, Bruce E.,Reitz, Allen B.,Graden, David W.,Almond, Harold R.Jr.
p. 1361 - 1364
(2007/10/02)
(E)-Selective Olefination of Aldehydes by means of gem-Dichromium Reagents Derived by Reduction of gem-Diiodoalkanes with ChHromium(II) Chloride
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Okazoe, Takashi,Takai, Kazuhiko,Utimoto, Kiitiro
p. 951 - 953
(2007/10/02)
Detailed Rate Studies on the Wittig Reaction of Nonstabilized Phosphorus Ylides via 31P, 1H, and 13C NMR Spectroscopy. Insight into Kinetic vs. Thermodynamic Control of Stereochemistry
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Maryanoff, Bruce E.,Reitz, Allen B.,Mutter, Martin S.,Inners, Ruth R.,Almond, Harold R. Jr.
p. 1068 - 1070
(2007/10/02)
HOMOALLYLIC SUBSTITUTION REACTIONS OF LITHIUM DIALKYL CUPRATES WITH CYCLOPROPYLCARBINYL HALIDES: MECHANISTIC CONSIDERATIONS
Highly reactive lithium dialkyl cuprates and 1-bromo-1-cyclopropylalkanes, 4, react to give good yields of the homoallylic substitution product, 6.Less reactive organocuprates react with 4 to give mixtures of 6 and the direct substitution product 7.These results are consistent with a copper(I) radical intermediate which undergoes facile rearrangement prior to reductive coupling.
Hrubiec, Robert T.,Smith, Michael B.
p. 1457 - 1468
(2007/10/02)
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