Bridging the Final Gap in Stereocontrolled Wittig Reactions: Methoxymethoxy-Armed Allylic Phosphorus Ylides Affording Conjugated Dienes with Highcis Selectivity
sodium amide), 2-alkenyltris(2-methoxymethoxyphenyl)phosphonium salts carrying an allyl, crotyl, or prenyl (3-methyl-2-butenyl) side chain condense with saturated or unsaturated aldehydes to give conjugated dienes with Z/E ratios ranging from 90:10 to > 99:1 and averaging 96:4. Owing to steric congestion, yields are only moderate (on average 41%; extremes 10-79%). The nonvolatile tris(2-methoxymethoxyphenyl)phosphine
The stereochemistry of the reactions between tris(2-methoxy-methoxyphenyl)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 â 200:1).
o-DPPB-Directed Copper-Mediated and -Catalyzed Allylic Substitution with Grignard Reagents
作者:Peter Demel、Manfred Keller、Bernhard Breit
DOI:10.1002/chem.200600225
日期:2006.8.25
explored as a directing leaving group in copper-mediated and copper-catalyzed allylicsubstitution with Grignardreagents. Complete control of chemo-, regio- and stereoselectivity with complete syn-1,3-chirality transfer was observed as a result of the directed nature of the reaction. No excess of organometallic reagent is required and the directing group can be recovered quantitatively. Coordination
2-Allylic-substituted isoureas underwent Wittig-type allylidenation of aldehydes in the presence of triphenylphosphine and 2 mol% of [Pd(PPh3)3] to give the corresponding conjugated olefins in tolerable to good yields.