An Efficient and Stereoselective Conversion of Lactones to Substituted Cyclic Ethers
摘要:
A general route to substituted cyclic ethers has been described by using nucleophilic addition of Grignard reagents to lactones in the presence of CeCl3 followed by the Lewis acid-induced deoxygenation of the corresponding hemiketals with Et3SiH. Stereoselective reduction of the 5-membered adducts to the disubstituted tetrahydrofurans has been also investigated.
transfer (LMCT) process from the consecutive excitation of the in situ formed copper(II) center. The chlorine radical abstracts a hydrogen atom selectively from C(sp3)–H bonds to generate the radical intermediate; meanwhile, the O2•– species interacted with the mimic to form mixed-valence species, giving the desired oxidization products with inherent product selectivity of copper monooxygenases and recovering
大自然的蓝图为扩大丰富金属在催化领域的应用提供了基本原则;然而,在一个用于选择性 C-H 键氧化的人工系统中同时模拟铜酶的结构和功能面临着巨大的挑战。在此,我们报告了一种组装人工单加氧酶的新方法,该方法利用双核 Cu 2 S 2 Cl 2簇来复制 Cu A酶的相同结构和催化作用。设计的单加氧酶 Cu-Cl-bpyc 促进明确定义的氧化还原电位,该电位最初通过光诱导电子转移激活 O 2 ,并通过来自原位形成的铜(II)中心的连续激发的配体到金属电荷转移(LMCT)过程。氯自由基选择性地从 C(sp 3 )–H 键中夺取一个氢原子,生成自由基中间体;同时,O 2 •–物种与模拟物相互作用形成混合价物种,提供具有铜单加氧酶固有产物选择性的所需氧化产物,并直接回收催化剂。该酶促方案具有出色的可回收性、良好的官能团耐受性和广泛的底物范围,包括一些生物学和药理学相关的靶标。机理研究表明,C-H 键断裂
Ultrathin 2D Cerium‐Based Metal–Organic Framework Nanosheet That Boosts Selective Oxidation of Inert C(sp3)H Bond through Multiphoton Excitation
Benefiting from framework confinement effects, synergistic effects of two active sites and/or flexibility of the ultrathin frameworknanosheets with high surface utilization, the observed activities increase in the order CeCl3/MV+ < bulk 3D MOF crystals < 2D MOF nanosheets in photocatalysis. This work not only contributes a new strategy to construct 3D layered MOFs and their ultrathin nanosheets but also
Electron-Transfer-Induced Reductive Cleavage of Phthalans: Reactivity and Synthetic Applications
作者:Ugo Azzena、Salvatore Demartis、Giovanni Melloni
DOI:10.1021/jo9604548
日期:1996.1.1
The behavior of phthalan (1a) was investigated under conditions of electron transfer from alkali metals in aprotic solvents. Reaction with lithium in the presence of a catalytic amount of naphthalene in THF led to the reductive cleavage of an arylmethyl carbon-oxygen bond, with formation of a stable dilithium compound. Trapping of this intermediate with several electrophiles (alkyl halides, carbonyl derivatives, CO2) was successful. The extension of this procedure to several substituted phthalans (1b-i) was investigated, and the regiochemistry as well as the synthetic usefulness of these reactions are discussed.