Photochemical C−C Bond Cleavage of 1,2-Diarylcyclopropanes Bearing an Acetylphenyl Group. Generation and Observation of Triplet 1,3-Biradicals
摘要:
The photochemical properties of 1,2-diarylcyclopropanes bearing an acetylphenyl group were studied by product analysis and laser flash photolysis. All cyclopropanes showed efficient cis-trans photoisomerization followed by inefficient isomerization to 1,3-diarylpropenes. All the products were unquenched by the addition of triplet quencher, 2-methyl-1,3-butadiene (E-T similar or equal to 60 kcal mol(-1)), whereas molecular dioxygen gave oxygenated products. Triplet 1,3-biradicals generated from a short-lived acetophenone-like triplet (less than or similar to 1 ns) were observed as intermediates in these reactions through nanosecond laser flash photolysis. Polar substituent effects on the lifetime of the 1,3-biradicals were small, except for a heavy atom effect in the case of Br. Spin-orbit coupling calculations on model 1,3-biradicals show a negligible effect on polar substituent and thus predict a negligible effect on the intersystem crossing rate. Conjugated biradicals in general now seem unlikely to show the "ionic character effect" on intersystem crossing suggested by the work of Salem and Rowland.
Palladium-Catalyzed Heck-Type Reactions of Allylic Esters with Arylboronic Acids or Potassium Aryltrifluoroborates
作者:Bo Yao、Yan Liu、Meng-Ke Wang、Jin-Heng Li、Ri-Yuan Tang、Xing-Guo Zhang、Chen-Liang Deng
DOI:10.1002/adsc.201100889
日期:2012.4.16
A selective and general route to (E)‐1,3‐diaryl‐prop‐1‐enes and (E)‐3‐arylallyl acetates has been developed by palladium‐catalyzed Heck‐type reactions of allylic esters with arylboronicacids or potassium aryltrifluoroborates. The present method selectively proceeds including β‐OAc elimination or β‐H elimination on the basis of the boronic acids. Whereas a variety of allylic esters were reacted with
Palladium-Catalyzed Selective Heck-Type Diarylation of Allylic Esters with Aryl Halides Involving a β-OAc Elimination Process
作者:Yan Liu、Bo Yao、Chen-Liang Deng、Ri-Yuan Tang、Xing-Guo Zhang、Jin-Heng Li
DOI:10.1021/ol1031552
日期:2011.3.4
Palladium-catalyzed selective Heck-type diarylation of allylic esters with arylhalides has been developed. Allylic esters are reacted with aryl iodides to provide the corresponding 1,3-diaryl propenes through a β-OAc elimination process. It is noteworthy that the methodology can be applied in constructing the indole and benzofuran skeletons.
Observation d'un diradical diaryl-1,3 propanediyle au cours de la photolyse du trans-bis-(acetyl-4' phenyl)-1,2cyclopropane et du trans-[acetyl-4' phenyl]-1 phenyl-2 cyclopropane
Observation d'un diradical diaryl-1,3 propanediyle au cours de la photolyse du trans-bis-(acetyl-4' phenyl)-1,2cyclopropane et du trans-[acetyl-4' phenyl]-1 phenyl-2 cyclopropane