nucleophilic catalyst for umpolung addition of azoles to electron-deficient allenes. This strategy offers a simple and efficient method for functional allylation of azoles under neutral conditions and affords heterocyclic substituted Michaelolefins. Furthermore, this catalytic methodology has been extended to addition–cyclization reactions between electron-deficient allenes or alkynes and pyrrole-2-carboxaldehyde
The initially formed N-phenylnitrone-intermediates are converted by a tandem-reaction (cycloaddition, Cope rearrangement, retro-Michael addition, and indolization) to 2-vinylindoles . Thus these indoles can be synthesized simply and stereoselectively in a one-pot reaction from N-phenylhydroxylamine , aldehydes , and electron-deficient allenes .
Regio- and Diastereoselective Insertion of Allenes into Stable Oxapalladacycles with a Metal-Bonded Stereogenic Carbon. Preparation of Contiguously Substituted 3,4-Dihydro-2<i>H</i>-1-Benzopyrans
作者:Genliang Lu、Helena C. Malinakova
DOI:10.1021/jo0486847
日期:2004.11.1
2-propadiene afforded benzopyran IV in 98% yield as the trans diastereomer in 92% de. In contrast, allenes with electron-withdrawing substituents yielded benzopyrans V with an E double bond exclusively. Nonracemic palladacycles featuring a palladium-bonded stereogenic carbon as the only element of asymmetry underwent the allene insertion with 63−93% retention of the stereochemical information, providing benzopyrans
研究了将单取代的异戊烯插入稳定的氧杂四环四环Ⅰ中。这项工作的目的是定义能够实现2,3-二取代的3,4-二氢-2 H -1-苯并吡喃的区域和非对映选择性合成的异戊二烯的空间和电子参数,而这不能通过相关方法制备。催化方案。在C-3和C-4碳上空间不受限的具有供电子性烷基取代基R的丙二烯与palladacycles I反应,以良好的收率(45-81%)提供苯并吡喃IV,仅作为顺式非对映异构体。在粗反应混合物中检测不到少于10%的区域异构苯并吡喃V。甲氧基1,2-丙二烯制得的苯并吡喃IV的产率为98%,反式非对映体的产率为92%。相比之下,具有吸电子取代基的丙二烯仅产生具有E双键的苯并吡喃V。以钯键合立体异构碳为非对称性唯一元素的非外消旋palladacycles进行了丙二烯插入,保留了63-93%的立体化学信息,从而提供了苯并吡喃IV或V在40−47%ee中。这些结果表明,O-键合的烯醇钯在插入
Organocatalytic Asymmetric Conjugate Addition to Allenic Esters and Ketones
作者:Petteri Elsner、Luca Bernardi、Giorgio Dela Salla、Jacob Overgaard、Karl Anker Jørgensen
DOI:10.1021/ja710689c
日期:2008.4.1
having different ring sizes, ring systems, and substituents in high yields and enantioselectivities. Glycine imine derivatives also undergo the asymmetric conjugate addition to electron-deficient allenes in high yields and with enantioselectivities in the range of 60-88% ee, thus providing a rapid entry to optically active alpha-vinyl-substituted alpha-amino acid derivatives. It is shown that the enantioselectivity
C−C-Bond Formation by the Palladium-Catalyzed Cycloisomerization/Dimerization of Terminal Allenyl Ketones: Selectivity and Mechanistic Aspects
作者:A. Stephen K. Hashmi、Thorsten L. Ruppert、Thomas Knöfel、Jan W. Bats
DOI:10.1021/jo970837l
日期:1997.10.1
conditions, besides the normal functional group tolerance known for palladium-catalyzed reactions, an interesting selectivity was observed with functional groups that are known to react either in palladium-catalyzed reactions or reactions catalyzed by other transition-metals. Thus aryl halides, terminal alkynes, 1,6-enynes, and alpha-allenic alcohols were tolerated. In the latter example the selective reaction