A Mild Dihydrobenzooxaphosphole Oxazoline/Iridium Catalytic System for Asymmetric Hydrogenation of Unfunctionalized Dialins
作者:Bo Qu、Lalith P. Samankumara、Shengli Ma、Keith R. Fandrick、Jean-Nicolas Desrosiers、Sonia Rodriguez、Zhibin Li、Nizar Haddad、Zhengxu S. Han、Keith McKellop、Scott Pennino、Nelu Grinberg、Nina C. Gonnella、Jinhua J. Song、Chris H. Senanayake
DOI:10.1002/anie.201408929
日期:2014.12.22
Air‐stable P‐chiral dihydrobenzooxaphosphole oxazoline ligands were designed and synthesized. When they were used in the iridium‐catalyzed asymmetrichydrogenation of unfunctionalized 1‐aryl‐3,4‐dihydronaphthalenes under one atmosphere pressure of H2, up to 99:1 e.r. was obtained. High enantioselectivities were also observed in the reduction of the exocyclic imine derivatives of 1‐tetralones.
Palladium(II)-catalyzed intramolecular addition of arylboronic acids to ketones
作者:Guixia Liu、Xiyan Lu
DOI:10.1016/j.tet.2008.05.056
日期:2008.7
A palladium(II)-catalyzed intramolecular addition of arylboronic acids to ketones was developed. Compared to Pd(OAc)2 catalysis system, cationic palladium complex with dppp as the ligand has higher catalytic activity and efficiency for wider scope of substrates. From this reaction, the normal addition product or the dehydrated product could be selectively furnished as controlled by additives. Highly
Picosecond to submillisecond photochromic reactions of 2,4-diphenyl-2H-benzopyran and 2,2,4-triphenyl2H-benzopyran have been investigated by time-resolved absorption spectroscopy. The C-O bond cleavage of the benzopyrans (closed forms) occurs via the first excited singlet state within 2 ps to produce vibrationally excited open forms in the ground electronic state. In the subnanosecond to submillisecond time domain, several decay components with almost the same spectral profiles are observed. These components are assigned to respective stereoisomers with respect to two double bonds and one single bond of the open enone forms. From the pump-laser power dependencies of the yields of the open forms, it is suggested that the photocleavage gives at first only the open forms revertible to the closed form by a single-bond rotation, and that the photoexcitation of the first generated open forms gives rise to other open forms which need a double-bond rotation for reversion to the closed form. The photochromic reactions of a series of 2H-benzopyrans bearing substituents on the pyran ring have also been studied using nanosecond time-resolved absorption spectroscopy. The size of a substituent in the 4-position fairly affects the rate constants of the thermal reversion of the open form to the closed form.