Photocyclization and photooxidation of 3-styrylthiophene
摘要:
The photocyclization, dye-sensitized photooxidation and auto-photooxidation of 3-styrylthiophene have been examined, cis-3-Styrylthiophene undergoes photochemical cis-trans isomerization and cyclization to dihydronaphtho-[1,2-b]thiophene. The quantum efficiency for photocyclization in nonpolar solvents is greater than that in polar solvents. Dye-sensitized photooxidation of 3-styrylthiophene gives benzaldehyde and 3-thiophenecarboxaldehyde. This oxidation proceeds via a superoxide radical anion pathway rather than singlet oxygen pathway. In the presence of oxygen photoirradiation of 3-styrylthiophene solution results in photocyclization, oxidation and dimerization. The mechanism of the latter two reactions was described in terms of formation of a charge transfer complex between oxygen and the substrate. (C) 2000 Elsevier Science Ltd. All rights reserved.
Diarylethenes were obtained from the corresponding ethenyl sulfones by photocatalyzed desulfonylation using UV or blue LEDs. When perylene and i-Pr2NEt were used as a photocatalyst and a sacrificing reagent, respectively, this desulfonylation proceeded smoothly to afford the desired ethenes with the functional groups such as chloro, alkoxy and heteroaromatic rings remaining untouched. The use of a flow photoreactor enabled this desulfonylation to proceed more rapidly to finish in an hour of residence time.
Stereodivergent Alkyne Reduction by using Water as the Hydrogen Source
作者:Santhosh Rao、Kandikere Ramaiah Prabhu
DOI:10.1002/chem.201803147
日期:2018.9.18
homogeneous Pd‐catalyzed stereodivergent reduction of alkynes to Z and E alkenes by using H2O as the H2 source is presented. Mediated by a diboron reagent, the transfer hydrogenation has been accomplished to yield the desired geometrical isomer by rational ligand selection. The switchable stereoselectivity achieved using simple phosphine ligands is generally excellent. D2O has also been used as a D2 source
Copper-catalysed, diboron-mediated <i>cis</i>-dideuterated semihydrogenation of alkynes with heavy water
作者:Xiaowei Han、Jiefeng Hu、Cheng Chen、Yu Yuan、Zhuangzhi Shi
DOI:10.1039/c9cc03213d
日期:——
efficiently mediate the transfer of two D atoms from heavy water directly onto alkynes through copper-catalysed cis-selective semihydrogenation. Avoiding the use of costly and flammable D2 gas, this safe and practical process can proceed with excellent chemoselectivity and stereoselectivity. Utilizing the present method as the key step, the formal asymmetrictotalsynthesis of d2-deuterium-labeled cis-combretastatin
were formed. Stilbene derivatives also gave two regioisomers under the same reaction conditions. However, 1-methoxy-4-(4-nitrostyryl)benzene provided a single cycloaddition product. The observed regioselectivity was discussed in terms of atomic charge distribution on the olefinic double bond carbon atoms. Furthermore, activation barriers for transition states were calculated.
Ruthenium-Catalyzed <i>E</i>-Selective Alkyne Semihydrogenation with Alcohols as Hydrogen Donors
作者:Andreas Ekebergh、Romain Begon、Nina Kann
DOI:10.1021/acs.joc.9b02721
日期:2020.3.6
Selective direct ruthenium-catalyzed semihydrogenation of diaryl alkynes to the corresponding E-alkenes has been achieved using alcohols as the hydrogen source. The method employs a simple ruthenium catalyst, does not require external ligands, and affords the desired products in > 99% NMR yield in most cases (up to 93% isolated yield). Best results were obtained using benzyl alcohol as the hydrogen