Intramolecular Palladium(II)-Catalyzed 1,2-Addition to Allenes
作者:Catrin Jonasson、Attila Horváth、Jan-E. Bäckvall
DOI:10.1021/ja001748k
日期:2000.10.1
were performed in the presence of LiBr with Pd(OAc)2 as the catalyst. Two different reoxidants, p-benzoquinone or Cu(OAc)2, were used, the choice of oxidant being dependent on the substrate. The reaction proceeds through an external nucleophilic attack (Br-) on a (π-allene)palladium complex to produce a (π-allyl)palladium intermediate. Subsequent intramolecular attack by the second internal nucleophile
钯 (II) 催化分子内 1,2-加成到被内部亲核试剂取代的丙二烯。羧酸、醇、N-取代酰胺和氨基甲酸酯用作钯催化反应中的内部亲核试剂,以良好的分离产率提供内酯、四氢吡喃、四氢呋喃、吡咯烷和恶唑烷酮。该反应在 LiBr 存在下以 Pd(OAc)2 作为催化剂进行。使用了两种不同的再氧化剂,对苯醌或 Cu(OAc)2,氧化剂的选择取决于底物。该反应通过对(π-丙二烯)钯络合物的外部亲核攻击(Br-)进行,以产生(π-烯丙基)钯中间体。随后第二个内部亲核试剂的分子内攻击产生产物。中间体(π-烯丙基)钯配合物被分离和表征。研究了反应的范围和局限性及其机理和选择性,在不同的反应...
Highly regioselective isomerization of acetylenes to allenes
Internal acetylenes bearing a hydroxyl group at the appropriate position of an alkyl chain, isomerized regioselectively to allenes by the treatment with alkyl lithium in the presence of ,,,-tetramethylethylenediamine.
Highly Regio- and Stereoselective Cyclic Iodoetherification of 4,5-Alkadienols. An Efficient Preparation of 2-(1′(<i>Z</i>)-Iodoalkenyl)tetrahydrofurans
作者:Bo Lü、Xinpeng Jiang、Chunling Fu、Shengming Ma
DOI:10.1021/jo802079b
日期:2009.1.2
In this paper, an efficient way to synthesize 2-(1'(Z)-iodoalkenyl)tetrahydrofurans from 4,5-alkadienols and 12 was developed. The reaction of the 4,5-allenols with a substituent in the 3-position afforded the trans-2,3-disubstituted tetrahydrofurans with very high diastereoselectivity. However, when the axially optically active 4,5-allenol was treated with 12 in n-hexane, the efficiency for chirality transfer was low. This problem was circumvented by conducting the reaction in CH2Cl2 at room temperature and applying N-iodosuccinimide as the electrophilic reagent; however, the Z/E ratio for the products is much lower. Highly optically active Z-products may be prepared via the kinetic resolution via a Sonogashira coupling reaction with propargyl alcohol.