Utilization of neutral alumina as a mild reagent for the selective cleavage of primary and secondary silyl ethers
摘要:
The selective cleavage of primary and secondary trimethylsilyl (TMS), triisopropylsilyl (TIPS), tert-butyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) ethers with neutral alumina under very mild conditions is described. The method involves utilization of the support, previously activated by heating at 80 degrees C/0.1 torr for 16 h and later deactivated with variable amounts of water (1.5-4.5%), in 50:1 ratio with regard to the substrate and in the presence of non-polar solvents, like hexane. The deprotection rate depends on the steric bulkiness of the silicon substituents, following the order TMS > > TBDMS approximate to TIPS > TBDPS, as well as on the type of the attached carbon. The procedure can discriminate between different silyl groups located at equivalent positions of the same molecule affording the corresponding monoprotected alcohols in very good yields.
报道了使用衍生自生物可再生原料的单体合成聚甲硅烷基醚(PSE)。AB型单体是由十一碳烯酸通过氢化硅烷化和还原反应合成的,并且聚合反应是由富含土的金属盐催化的。获得了高摩尔质量的产物,并且通过改变反应中AA型单体的量来控制聚合度。PSE具有良好的热稳定性和较低的玻璃化转变温度(T g ≈−67°C)。为了证明PSE的效用,聚氨酯是由低摩尔质量的羟基telechelic PSE合成的。
Stereoselective Iodocyclopropanation of Terminal Alkenes with Iodoform, Chromium(II) Chloride, and <i>N</i>,<i>N</i>,<i>N</i>‘,<i>N</i>‘-Tetraethylethylenediamine
Chemoselectivity of a reagent for (E)-olefination of aldehydesderived by reduction of iodoform with chromium(II) chloride in THF changes markedly by addition of TEEDA (N,N,N',N'-tetraethylethylenediamine), and trans-iodocyclopropanes are produced stereoselectively from terminal alkenes by treatment with the base-added reagent system. The iodocyclopropanation occurs only at terminal double bonds, and
通过加入 TEEDA(N,N,N',N'-四乙基乙二胺)和反式碘代环丙烷,通过在 THF 中用氯化铬 (II) 还原碘仿而得到的醛的 (E)-烯化试剂的化学选择性显着变化通过用加碱试剂系统处理,从末端烯烃立体选择性地产生。碘环丙烷化仅发生在末端双键处,同一分子中的二取代和三取代双键保持不变。醇、醚、甲硅烷基醚、酯、叔胺和酰胺基等官能团与反应条件相适应。
Heterosubstituted cyclopropanation of alkenes with organochromium reagents derived from heterosubstituted dihalomethanes, CrCl2, and tetraalkylethylenediamine
stereoselectively fromterminal alkenes by treatment with a reagent derivedfrom iodoform, chromium(II) chloride, and TEEDA (N,N,N′,N′-tetraethylethylenediamine) in THF. Similarly, cyclopropylsilanes and cyclopropylboronic esters are obtained by using R3SiCHI2, and a combination of Cl2CHB(OR)2 and LiI instead of iodoform, respectively. The heterocyclopropanation occurs selectively at terminaldoublebonds, and