Bismuth-Substituted “Sandwich” Type Polyoxometalate Catalyst for Activation of Peroxide: Umpolung of the Peroxo Intermediate and Change of Chemoselectivity
作者:Srinivasa Rao Amanchi、Alexander M. Khenkin、Yael Diskin-Posner、Ronny Neumann
DOI:10.1021/acscatal.5b00066
日期:2015.6.5
formation of a nucleophilic peroxo intermediate. There are two lines of evidence that support the formation of a reactive nucleophilic peroxo intermediate: (1) More electrophilic sulfoxides are more reactive than more nucleophilic sulfides, and (2) nonfunctionalized aliphatic alkenes and dienes showed ene type reactivity rather than epoxidation pointing toward “dark” formation of singletoxygen from the
W VI,Mo VI,V V和Ti IV化合物用过氧化物对烯烃进行环氧化是公认的方法,并且公认的是,活性中间过氧化物对亲核底物是亲电子的。Polyoxotungstates,例如,那些在“三明治”结构,[WZn(TM-L)的2(ZnW 9 ö 34)2 ] q - ,其中TM =过渡金属和L = H 2 O,在过去已经发现是出色的环氧化催化剂。现已发现,用刘易斯基本的Bi III代替进入“三明治”多金属氧酸盐结构的末端位置,生成[Zn 2 Bi III 2(ZnW 9 O 34)2 ] 14–导致明显的过氧化物种类的形成和亲核过氧化物中间体的形成。有两条证据支持反应性亲核过氧中间体的形成:(1)更多的亲电子亚砜比更多的亲核硫化物更具反应性;(2)未官能化的脂肪族烯烃和二烯显示出烯型反应性,而不是环氧化,指向“亲核中间体过氧物种形成单线态氧的“暗”形。烯丙醇的反应比烯烃快得多,但对醇的C–H
Employing Water as the Hydride Source in Synthesis: A Case Study of Diboron Mediated Alkyne Hydroarylation
We present an approach to utilize water as the hydride source via Pd(II)/Pd(0) catalysis. As a case study, we have achieved a diboron mediated Pd(II)-catalyzed hydroarylation of alkynes using arylboronic acids. This approach not only complements conventional reactivity of Pd via Pd(0)/Pd(II) cycle for the hydroarylation but also utilizes water as the hydride source. We believe this would particularly
mechanistic investigations, including (1)H and (31)P(1)H} NMR studies; isolation and characterization of several catalytic intermediates, Pt(xantphos)Cl(2), Pt(eta(2)-C(3)H(5)OH)(xantphos), etc; confirmation of the structure of [Pt(eta(3)-allyl)(xantphos)]OTf by X-ray crystallographic analysis; and crossover experiments, suggested that formation of the pi-allylplatinum complex through the elimination of water
Tungsten-Catalyzed Asymmetric Epoxidation of Allylic and Homoallylic Alcohols with Hydrogen Peroxide
作者:Chuan Wang、Hisashi Yamamoto
DOI:10.1021/ja411379e
日期:2014.1.29
A simple, efficient, and environmentally friendly asymmetricepoxidation of primary, secondary, tertiary allylic, and homoallylic alcohols has been accomplished. This process was promoted by a tungsten–bishydroxamic acid complex at room temperature with the use of aqueous 30% H2O2 as oxidant, yielding the products in 84–98% ee.
伯、仲、叔烯丙醇和高烯丙醇的简单、高效和环境友好的不对称环氧化已经完成。该过程在室温下由钨-双异羟肟酸配合物促进,使用 30% H2O2水溶液作为氧化剂,产生 84-98% ee 的产物。
Allylic alcohol synthesis by Ni-catalyzed direct and selective coupling of alkynes and methanol
作者:Herong Chen、Zhijun Zhou、Wangqing Kong
DOI:10.1039/d1sc02625a
日期:——
nickel-catalyzed direct coupling of alkynes and methanol, providing direct access to valuable allylicalcohols in good yields and excellent chemo- and regioselectivity. The approach features a broad substrate scope and high atom-, step- and redox-economy. Moreover, this method was successfully extended to the synthesis of [5,6]-bicyclic hemiacetals through a cascade cyclization reaction of alkynones and methanol