Geometric
<i>E</i>
→
<i>Z</i>
Isomerisation of Alkenyl Silanes by Selective Energy Transfer Catalysis: Stereodivergent Synthesis of Triarylethylenes via a Formal
<i>anti</i>
‐Metallometallation
作者:Svenja I. Faßbender、John J. Molloy、Christian Mück‐Lichtenfeld、Ryan Gilmour
DOI:10.1002/anie.201910169
日期:2019.12.16
An efficient geometrical E→Z isomerisation of alkenyl silanes is disclosed via selective energy transfer using an inexpensive organic sensitiser. Characterised by operational simplicity, short reaction times (2 h), and broad substrate tolerance, the reaction displays high selectivity for trisubstituted systems (Z/E up to 95:5). In contrast to thermal activation, directionality results from deconjugation
Yttrium-Mediated Conversion of Vinyl Grignard Reagent to a 1,2-Dimetalated Ethane and Its Synthetic Application
作者:Ryoichi Tanaka、Hiroaki Sanjiki、Hirokazu Urabe
DOI:10.1021/ja077992u
日期:2008.3.1
ethane was generated from a vinyl Grignard reagent in the presence of yttrium(III) chloride, sodium cyclopentadienide, and diisobutylaluminum hydride (Dibal). This reagent enables the regio- and stereoselective (metaloethyl)metalation of acetylenes to produce ethylated alkenes after hydrolysis. In addition to simple hydrolysis, further carbon−carbon bond formation or functionalization at the metaloethyl
The contra-thermodynamic E→Zisomerization of vinyl silanes was reported using rac-BINAP as the photocatalyst. This reaction proceeds via the in situ formation of a chromophoric species, in the presence of catalyst. Under irradiation at 405 nm the interconversion of E-isomers into the Z-congeners were carried out in good to excellent yields and outstanding Z/E selectivities (18 examples) and the reaction
The addition of dialkylzincs or diphenylzinc to substituted phenylacetylenes in the presence of catalytic amounts of Ni(acac)(2) in THF : NMP mixtures produces syn-carbozincation products with good to excellent regio-and stereoselectivity. After quenching with an electrophile (iodine, acyl chloride, allyl bromide) tetrasubstituted olefines are obtained in good to satisfactory yields. An intramolecular version of the reaction is possible using a terminal triple bond bearing an iodine at a remote position. More substituted iodo-alkynes furnish only reductive elimination products. An application to a stereoselective synthesis of (Z)-tamoxifen (Z: E > 99: 1) has been developed. (C) 1998 Elsevier Science Ltd. All rights reserved.
Wong, Ken-Tsung; Ni, Zhi-Jie; Luh, Tien-Yau, Journal of the Chemical Society. Perkin transactions I, 1991, # 12, p. 3113 - 3116