Prototropic control of the di-π-methane photorearrangement
作者:Miguel Garcia-Garibay、John R. Scheffer、Darrell G. Watson
DOI:10.1039/c39890000600
日期:——
state of protonation and hydrogen bonding in a monoester (1) of dibenzobarrelene-11,12-dicarboxylic acid (9,10-etheno-9,10-dihydroanthracene-11,12-dicarboxylic acid) controls the regioselectivity of its di-π-methanephotorearrangement.
Prototropic control of organic photochemistry. Hydrogen bonding effects on the di-.pi.-methane photorearrangement
作者:Miguel A. Garcia-Garibay、John R. Scheffer、Darrel G. Watson
DOI:10.1021/jo00027a043
日期:1992.1
The IR and UV spectra as well as the photochemistry of the isopropyl monoester of dibenzobarrelene dicarboxylic acid 2 were analyzed in detail in several media. A correlation was found between the photochemical results and the spectroscopically detected hydrogen-bonded structures of 2. An equilibrium between dimeric (2-HD) and intramolecularly hydrogen bonded (2-HI) structures was detected by IR spectroscopy in nonpolar solvents having weak hydrogen-bond-accepting capabilities. The ratio of the two regioisomeric dibenzosemibullvalene products 3 and 4 formed in the di-pi-methane photorearrangement of 2 was found to correlate with such an equilibrium, and it was concluded that intramolecular (2-HI) and dimeric (2-HD) hydrogen-bonded structures display significantly different photochemical reactivity. The infrared spectra and the photoproduct ratio in polar solvents possessing hydrogen-bond-accepting capabilities (e.g., acetonitrile), on the other hand, turned out to be concentration independent. High regioselectivity was found in the solid state where the dimer 2-HD is the only species, leading to 4 as the major product. In contrast, 3 was obtained preferentially in aqueous sodium bicarbonate solutions where 2 exists as the carboxylate anion. Supporting evidence regarding the different hydrogen bonding arrangements in 2 was found in the solvent effects on its UV spectra.