Stereoselective Synthesis and Reactivity of Dienyl Zirconocene Derivatives
作者:Ilan Marek、Nicka Chinkov、Swapan Majumdar
DOI:10.1055/s-2004-829189
日期:——
Stereoselective dienyl zirconocene derivatives have been prepared via a tandem allylic C-H bond activation isomerization-elimination reaction. These reagents can be either trapped directly with electrophiles or transmetalated to copper to participate in several carbon-carbon bond formations. When the transmetalation is performed on allylic as well as vinylic zirconocene derivatives, the reaction occurs with inversion of stereochemistry of the dienyl system.
Three types of products by carbon nucleophiles toward methoxyphenylacetylenic sulfones
作者:Chia-Yi Cheng、Minoru Isobe
DOI:10.1016/j.tet.2011.09.078
日期:2011.12
Methoxy-arylacetylenic sulfones were examined to react with various carbanion nucleophiles to result in the three types of products; thus, (i) nucleophiles (MeLi·LiBr, Vinyl MgBr, LiCH2CN) showed the α-addition, however, (ii) Li–CC–TMS afforded β-addition (conjugate addition) products. The (iii) displacement reaction through α-addition/isomerization/trans-elimination was enhanced by the presence of ortho-methoxy
检查了甲氧基-芳基乙炔砜与各种碳负离子亲核试剂反应生成三种类型的产物。因此,(i)亲核试剂(MeLi·LiBr,乙烯基MgBr,LiCH 2 CN)显示出α加成,但是,(ii)Li– CC C–TMS提供了β加成(共轭加成)产物。通过在高温下存在邻甲氧基,可以增强通过α-加成/异构化/反式消除的(iii)置换反应。质子溶剂中的杂原子亲核试剂(氮,氧或硫原子)仅提供了所报道的缀合物加成产物。
New Reactions of -Halocarbanions: Simple Synthesis of Substituted Tetrahydrofurans
gamma-halocarbanions that undergo fast intramolecular substitution of the halogen to produce substituted cyclopropanes. We found that these short-lived carbanionic intermediates can be trapped with active external electrophilic partners, such as aldehydes, to give the aldol anions. These anions then undergo rapid intramolecular substitution of chloride to produce 2,3-disubstituted tetrahydrofurans. Under the right
New reactions of γ-halocarbanions: underestimated reactive intermediates in organic synthesis
作者:M. Barbasiewicz、M. Judka、M. Makosza
DOI:10.1007/s11172-005-0043-8
日期:2004.9
Michael acceptors to give anionic adducts, which undergo intramolecular substitution to give substituted tetrahydrofurans, pyrrolidines, and cyclopentanes. This has underlain a new method for the synthesis of these valuable ring systems. We have determined the acidity of the γ-halocarbanion precursors and have shown that the halogen atoms in the γ-position relative to the carbanion center exert a significant
New Approach to the Stereoselective Synthesis of Metalated Dienes via an Isomerization−Elimination Sequence
作者:Nicka Chinkov、Swapan Majumdar、Ilan Marek
DOI:10.1021/ja027027y
日期:2002.9.1
Treatment of Cp2ZrBu2 with enol ether containing a remote double bond lead to conjugated metalated diene as single isomer via a tandem isomerization-elimination sequence. 2-Arylsulfonyl 1,3-dienes can also be used as a source of dienyl zirconocene derivatives, and the stereochemistry of the diene is dependent on the transmetalation reaction.