Rhodium-Catalyzed Selective Partial Hydrogenation of Alkynes
摘要:
The cationic rhodium complex [Rh((PPr3)-Pr-c)(2)(eta(6)-PhF)](+)[B{3,5-(CF3)(2)C6H3}(4)](-) ((PPr3)-Pr-c = triscyclopropylphosphine, PhF = fluorobenzene) was used as a catalyst for the hydrogenation of the charge-tagged alkyne [Ph3P(CH2)(4)C2H](+)[PF6](-). Pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS) was used to monitor reaction progress. Experiments revealed that the reaction is first order in catalyst and first order in hydrogen, so under conditions of excess hydrogen the reaction is pseudo-zero order. Alkyne hydrogenation was 40 times faster than alkene hydrogenation. The turnover-limiting step is proposed to be oxidative addition of hydrogen to the alkyne (or alkene)-bound complex. Addition of triethylamine caused a dramatic reduction in rate, suggesting a deprotonation pathway was not operative.
Surgical reduction: N‐Heterocyclic carbene–borane complexes such as depicted are neutral, organic soluble analogues of borohydride anions with a weak hydridic character, compatible with organometallic catalysis. They are applicable for surgical reductions in complex, multifunctional molecules.
Selective Isomerization of Terminal Alkenes to (<i>Z</i>)-2-Alkenes Catalyzed by an Air-Stable Molybdenum(0) Complex
作者:Joseph Becica、Owen D. Glaze、Derek I. Wozniak、Graham E. Dobereiner
DOI:10.1021/acs.organomet.7b00914
日期:2018.2.12
Positional and stereochemical selectivity in the isomerization of terminal alkenes to internal alkenes is observed using the cis-Mo(CO)4(PPh3)2 precatalyst. A p-toluenesulfonic acid (TsOH) cocatalyst is essential for catalyst activity. Various functionalized terminal alkenes have been converted to the corresponding 2-alkenes, generally favoring the Z isomer with selectivity as high as 8:1 Z:E at high
使用顺式-Mo(CO)4(PPh 3)2预催化剂观察到末端烯烃异构化为内部烯烃的位置和立体化学选择性。甲p -甲苯磺酸(TsOH)助催化剂为催化剂活性是必需的。各种官能化的末端烯烃已被转化为相应的2-烯烃,在高转化率下通常有利于Z异构体,其选择性高达8:1 Z:E。通过31 P NMR对催化剂引发机理的研究表明,顺式-Mo(CO)4(PPh 3)2在高温下与TsOH反应生成磷化氢键合的Mo氢化物(MoH)物种。催化可通过将末端烯烃的2,1-插入MoH基团和立体选择性β-氢化物消除以产生(Z)-2-烯烃来进行。
Enantioselective Nickel‐Catalyzed Migratory Hydrocyanation of Nonconjugated Dienes
作者:Rongrong Yu、Shanmugam Rajasekar、Xianjie Fang
DOI:10.1002/anie.202008854
日期:2020.11.23
Metal‐catalyzed chain‐walking reactions have recently emerged as a powerful strategy to functionalize remote positions in organic molecules. However, a chain‐walking protocol for nonconjugated dienes remains scarcely reported, and developments are currently ongoing. In this Communication, a nickel‐catalyzed asymmetric hydrocyanation of nonconjugated dienes involving a chain‐walking process is demonstrated
Synthetic studies towards the phomactins. Concise syntheses of the tricyclic furanochroman and the oxygenated bicyclo[9.3.1]pentadecane ring systems in phomactin A
作者:Kevin M Foote、Christopher J Hayes、Matthew P John、Gerald Pattenden
DOI:10.1039/b307985f
日期:——
A concise synthesis of the tricyclic furanochroman unit 3 found in the PAF antagonist phomactin A (1) isolated from the marine fungus Phoma sp., is described. In complementary studies, a variety of synthetic routes towards the bicyclo[9.3.1]pentadecaneringsystem 4 in phomactin A were explored. These studies culminated in a synthesis of the substituted ringsystem 79 containing all the carbon atoms
Organophosphonium salt was converted into deuterium labelled ones under hydrothermal condition in the presence of molecular sieves. The hydrothermal condition can be obtained by either heating D2O in an autoclave or irradiating with microwave to D2O in a sealed vial.