Preparation, alkylation reactions, and conformational analysis of esters of phospholanic acid. Preparation and reactivity of (2S*,5S*)-1,2,5-tribenzyl-1-oxophospholane
摘要:
Optimum conditions for the reaction of 1,4-butanediyldimagnesium dibromide and alkyl phosphorodichloridates are described. The general geometric requirements of the cyclization reaction transition state are discussed. Alkylation reactions of phospholanate esters 2b and 2c are reported. Conformational analysis of various phospholanate esters is discussed in terms of 3J(PC) and 3J(PH) data, NOE experiments, and crystal structures of related phospholane derivatives. trans-2,5-Dibenzyl phosphinate esters 15b and 15c were converted to (2S*,5S*)-1,2,5-tribenzyl-1-oxophospholane 18 by reductive alkylation. Phosphine oxide 18 was shown to participate in an olefination reaction with 4-tert-butylcyclohexanone.
Nickel-Catalyzed Arylboration of Alkenylarenes: Synthesis of Boron-Substituted Quaternary Carbons and Regiodivergent Reactions
作者:Liang-An Chen、Alan R. Lear、Pin Gao、M. Kevin Brown
DOI:10.1002/anie.201904861
日期:2019.8.5
A method for the construction of boron‐substituted quaternary carbons or diarylquaternary carbons by arylboration of highly substituted alkenylarenes is presented. A wide range of alkenes and arylbromides can participate in this reaction thus allowing for a diverse assortment of products to be prepared. In addition, a solvent dependent regiodivergent arylboration of 1,2‐disubstituted alkenylarenes
The 1H, 13C, and 15N NMRspectra of 5 exocyclic alkenes and 15 different ketimines obtained from cyclohexanone and derivatives using benzyl bromide and primary amines—are analyzed. Relative stereochemical and preferential conformations are determined by analyzing both the homonuclear coupling and the chemical shifts of the protons and carbon atoms in the aliphatic rings, which are directly related
Reduction of titanocene dichloride with dysprosium: access to a stable titanocene(<scp>ii</scp>) equivalent for phosphite-free Takeda carbonyl olefination
A new titanocene(ii) equivalent obtained from the reduction of titanocene dichloride with dysprosium allows phosphite-free and simplified Takeda carbonyl olefination reactions.
3,5-Bis(trifluoromethyl)phenyl Sulfones in the Julia–Kocienski Olefination – Application to the Synthesis of Tri- and Tetrasubstituted Olefins
作者:Diego A. Alonso、Mónica Fuensanta、Carmen Nájera
DOI:10.1002/ejoc.200600478
日期:2006.10
with carbonylcompounds employing phosphazene base P4-tBu at room temp. in THF, affording tri- and tetrasubstituted olefins in good yields. The Julia–Kocienski olefination between primary alkyl BTFP sulfones 8a,b and aromatic and aliphatic ketones affords the corresponding trisubstituted alkenes in good yields and low stereoselectivities. On the other hand, higher yields and stereoselectivities are
Double asymmetric synthesis: faster reactions are more selective and a model to estimate relative rate
作者:Christopher J. Richards、O. Stephen Ojo
DOI:10.1039/d3ob01048a
日期:——
centre. With one exception from fifteen examples, the selectivity factor (s = kfast/kslow) = kmatched/kmismatched. A model to estimate the relativerate of a fast-matched reaction vs. the corresponding slow-mismatched reaction is proposed. This model also provides insight into the basis of the selectivity displayed in the kinetic resolution procedures studied.
对映体纯底物的催化反应形成新的手性元素可能会导致催化剂的一种对映体(匹配对)比另一种对映体(错配对)具有更高的非对映选择性。使用导致形成新的立体中心的动力学解析程序的文献示例来研究匹配反应更快的假设。除 15 个示例中的一个例外外,选择性因子 ( s = k fast / k Slow ) = k匹配/ k不匹配。提出了一种估计快速匹配反应与相应的慢速错配反应的相对速率的模型。该模型还提供了对所研究的动力学拆分程序中显示的选择性基础的深入了解。