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.
SARTORI G.; CASIRAGHI G.; BOLZONI L.; CASNATI G., J. ORG. CHEM., 1979, 44, NO 5, 803-805
作者:SARTORI G.、 CASIRAGHI G.、 BOLZONI L.、 CASNATI G.
DOI:——
日期:——
Pharmaceutical preparations containing flavene or thioflavene derivatives, the use thereof, novel flavenes and thioflavenes, and processes for their manufacture
申请人:Zyma SA
公开号:EP0140830B1
公开(公告)日:1989-08-30
Heteroatom-Guided, Palladium-Catalyzed, Site-Selective CH Arylation of 4<i>H</i>-Chromenes: Diastereoselective Assembly of the Core Structure of Myristinin B through Dual CH Functionalization
palladium‐catalyzed direct arylation of 4H‐chromenes is reported. The CHfunctionalization is driven not only by the substituents and structure of the substrate but also by the coupling partner being used. The diastereoselectiveassembly of the corestructure of MyristininB has been achieved by using a dualCHfunctionalization strategy for regioselective direct arylation.