A novel and versatile synthetic method for picene derivatives is developed using the Pd-catalyzed intramolecular double cyclization of the corresponding 2,3-bis[(1Z)-2-phenylethenyl]-1,4-dichlorobenzenes, which are readily prepared by Suzuki–Miyaura cross-coupling reactions of polyhalobenzenes with (Z)-arylethenylboronates. The physical properties of the obtained picenes can be modified via introducing
Multisubstituted olefins are efficiently prepared by the zirconocene-mediated regio- and stereoselective coupling between 1-alkynylboronates and ethylene, followed by sequential transformation in moderate to high yields. The proper combination of substrates and reaction conditions is important for high yields. The synthesis of various tetrasubstituted alkenes in a regio- and stereocontrolled manner
Stereoselective Synthesis of Trisubstituted Alkenylboron Reagents by Boron-Wittig Reaction of Ketones
作者:Sheila Namirembe、Chenpeng Gao、Ryan P. Wexler、James P. Morken
DOI:10.1021/acs.orglett.9b01663
日期:2019.6.7
Application of the boron-Wittigreaction to ketone electrophiles provides a straightforward route to trisubstituted alkenylboronic esters. With either a pentamethyldiethylenetriamine or trimethyl-1,4,7-triazacyclononane additive, the olefination can occur with very high levels of stereocontrol and in good chemical yield.
Contra-Thermodynamic, Photocatalytic <i>E</i>
→<i>Z</i>
Isomerization of Styrenyl Boron Species: Vectors to Facilitate Exploration of Two-Dimensional Chemical Space
作者:John J. Molloy、Jan B. Metternich、Constantin G. Daniliuc、Allan J. B. Watson、Ryan Gilmour
DOI:10.1002/anie.201800286
日期:2018.3.12
Designing strategies to access stereodefined olefinic organoboron species is an important synthetic challenge. Despite significant advances, there is a striking paucity of routes to Z‐α‐substituted styrenyl organoborons. Herein, this strategic imbalance is redressed by exploiting the polarity of the C(sp2)−B bond to activate the neighboring π system, thus enabling a mild, traceless photocatalytic isomerization
The photocatalytic contra-thermodynamic E→Z isomerization of vinyl boronates by using a binaphthol catalyst is disclosed. The reaction, based on the transient formation of a suitable chromophore with a BINOL derivative as the catalyst, allowed geometrical isomerization in good-to-excellent Z/E ratio and excellent-to-quantitative yields. The mechanism of this E→Z contra-thermodynamic isomerization was