Elimination of β-Thioalkoxy Alcohols under Mitsunobu Conditions. A New Synthesis of Conjugated Enynes from Propargylic Dithioacetals
作者:Chih-Wei Chen、Tien-Yau Luh
DOI:10.1021/jo8013885
日期:2008.11.7
Treatment of propargylic dithiolanes 1 with (n)BuLi followed by a carbonyl electrophile yields the corresponding homopropargylic alcohol 3. Upon treatment with 2 equiv of PPh3 and DIAD, elimination of SR and OH moieties from 3 affords the corresponding olefins 4 in moderate to good yield. The reaction can be considered an alternative of McMurry coupling of two different carbonyl equivalents.
A CoCl2·6H2O/Zn reagent using 2-(2,6-diisopropylphenyl)iminomethylpyridine (dipimp), 1,2-bis(diphenylphosphino)ethane (dppe), or 1,2-bis(diphenylphosphino)benzene (dppPh) as a ligand effectively catalyzed the cross-addition reaction of silylacetylene to internal alkynes. The reaction of some unsymmetrical internal alkynes, such as 3-arylpropargyl alcohols, proceeded in a highly regioselective manner
使用2-(2,6-二异丙基苯基)亚氨基甲基吡啶(dipimp),1,2-双(二苯基膦基)乙烷(dppe)或1,2-双(二苯基膦基)苯(dppPh)的CoCl 2 ·6H 2 O / Zn试剂)作为配体有效地催化了甲硅烷基乙炔与内部炔烃的交叉加成反应。一些不对称内部炔烃(例如3-芳基炔丙醇)的反应在dppe或dppPh的存在下以高度区域选择性的方式进行,但在dipimp的存在下产生了近1:1的区域异构体混合物。使用1-氘代2-甲硅烷基乙炔的反应结果表明,该反应涉及甲硅烷基乙炔C–H键与钴的直接氧化加成。
Stereoselective Iterative Convergent Synthesis of <i>Z</i>-Oligodiacetylenes from Propargylic Dithioacetals
A series of Bu-t-substituted Z-oligodiacetylenes (Z-ODAs) are synthesized from the reactions of allenyl/propargylic zinc reagents, obtained from the corresponding propargylic dithiolanes and BuLi, with dithiolane-substituted propargylic aldehydes followed by stereospecific elimination of beta-thioalkoxy alcohols under Mitsunobu conditions. The stereochemical assignments are based on NOE experiments. The X-ray structure of the hexamer further supports the Z configuration for each of the double bonds in these ODAs. The photophysical properties of these Z-ODAs have been examined and are compared with known related E- and Z-ODAs with different substituents.