Journal of Organic Chemistry p. 5139 - 5147 (1999)
Update date:2022-08-03
Topics:
Motschiedler, Krista
Gudmundsdottir, Anna
Toscano, John P.
Platz, Matthew
Garcia-Garibay, Miguel A.
The photochemistry of several arylalkyldiazo compounds has been investigated by steady-state direct and triplet sensitized irradiations and by nanosecond laser flash photolysis. Steady-state photolyses in methanol yielded methyl ethers and alkenes as the only significant products. Ethers were formed by denitrogenation of the diazo compound followed by carbene insertion into the MeO-H bond, and alkenes were obtained by 1,2-R (R = H,Ph) migrations both in the free carbene and in the singlet excited state of the diazo precursor. Evidence for the exited-state precursor reaction came from differences in product yields as a function of excitation wavelength and excited-state multiplicity. The yields of methyl ethers increased with increasing excitation wavelengths and were greatest upon triplet-state sensitization but were never the sole products formed despite expected diffusion-controlled insertion rates. Accordingly, the formation of pyridine ylides analyzed by laser flash photolysis in the presence of high concentrations of the base yielded relatively modest transient absorptions. The kinetics of the 1,2-H reaction, analyzed by time-resolved detection of stilbene in the case of 1,2-diphenylethylidenes, displayed fast and slow components. The fast component was attributed to stilbene that formed from the excited-state precursor and from the originally formed singlet carbene within the 20 ns pulse. The long-lived component was attributed to a spin-state equilibrated carbene with a lifetime of 70-80 ns in fluorocarbon solvents. Analysis of the long-lived component by a Stern-Volmer treatment upon addition of MeOH gave a lower limit for the reaction rate constant with a value of k1,2-H > 5 × 109 s-1 in a mixed Freon-methanol solvent. It is concluded that the combined effect of phenyl substituents at the carbon bearing the migrating group and high solvent polarity can lead to intramolecular 1,2-H shifts and 1,2-Ph migrations that are fast enough to compete with diffusion-controlled intermolecular MeO-H insertion in concentrated MeOH solutions.
View MoreTaixing Shenfeng Chemical Co., Ltd.
Contact:+86-523-87117033, 87117666
Address:4# Yinsanlu, Huangqiao town, Taixing, Jiangsu, China.
Shanghai shibo Chemical Co., Ltd
Contact:+86-021-60753516
Address:688 Qiushi Road, Jinshan High-tech Park, Shanghai, China,201512
Weifang Yukai Chemical Co.,Ltd.
website:http://www.yukaichem.com/en.html
Contact:+86-536-8865336
Address:binhai economic development zone,262737 shangdong,china
Changzhou Ansciep Chemical Co.,Ltd.
Contact:+86 519 8630 5871
Address:A-710 Boan International, 8 East Guangdian Road,Wujin,Changzhou
Dongguan Albiya Energy Science and Technology Co.,Ltd
Contact:+86-769-22181286
Address:Huanan Industial Park, Dongguan,China
Doi:10.1007/s00706-011-0662-8
(2012)Doi:10.1055/s-0036-1591860
(2018)Doi:10.1016/j.tet.2011.11.078
(2012)Doi:10.1021/jo00296a073
(1990)Doi:10.1002/chem.201200294
(2012)Doi:10.1021/jo00976a017
(1972)