PHOTOCHEMISTRY OF THE 9-HYDROXYXANTHENYL RADICAL IN THE LASER-JET - EVIDENCE FOR PHOTOCHEMICALLY INDUCED, REGIOSELECTIVE RADICAL COUPLING

被引:9
作者
ADAM, W
KITA, F
机构
[1] The Institute of Organic Chemistry, University of Würzburg, Würzburg, Am Hubland
关键词
D O I
10.1021/ja00088a002
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The conventional irradiation (low intensity) of xanthone in ethanol was observed to produce pinacol 3 by photoreductive coupling and 9-hydroxy-9-(1-hydroxyethyl)-9H-xanthene (4) by head-to-head cross-coupling between the resultant 9-hydroxyxanthenyl (2) and 1-hydroxyethyl radicals. Under laser-jet conditions (high intensity), in addition to products 3 and 4, 3-(1-hydroxyethyl)-9H-xanthen-9-one (5d) was obtained as the major head-to-tail cross-coupling product. The observed dependence of the product ratio of 4 and 5d on the irradiation intensity is rationalized in terms of the higher spin density in the aryl rings, particularly at the 3-position (para to the hydroxy-substituted carbon atom), of the electronically excited 9-hydroxyxanthenyl radical (2'). For the ground state radical 2, as expected, the majority of spin density resides at the hydroxy-substituted carbon atom and, thus, constitutes the precursor to the head-to-head cross-coupling product 4. The theoretical spin densities for the ground and excited state 9-hydroxyxanthenyl radicals 2, calculated by semiempirical MO methods (PM3), indicate that upon photoexcitation the electron density in the SOMO shifts from the hydroxy-substituted radical center (ground state) to the aromatic pi-system (first excited state) and is concentrated at the 1a- and 3-positions.
引用
收藏
页码:3680 / 3683
页数:4
相关论文
共 38 条
[11]   ON PHOTOREDUCTION OF BENZOPHENONE IN ISOPROPYL ALCOHOL [J].
FILIPESC.N ;
MINN, FL .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1968, 90 (06) :1544-+
[12]   LASER PHOTOLYSIS STUDIES OF TRIPLET-STATE OF XANTHONE AND ITS KETYL RADICAL IN FLUID SOLUTION [J].
GARNER, A ;
WILKINSON, F .
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS II, 1976, 72 :1010-1020
[13]   SYNTHESIS OF DIAMINOXANTHONES [J].
GOLDBERG, AA ;
WALKER, HA .
JOURNAL OF THE CHEMICAL SOCIETY, 1953, (MAY) :1348-1357
[14]  
JEANDRAU JP, 1979, J CHEM RES SYNOP, V6, P186
[15]   EFFECT OF SUBSTITUTION ON PHOTOREDUCTION OF SOME HINDERED BENZOPHENONES [J].
LAMB, FA ;
VITTIMBE.BM .
JOURNAL OF ORGANIC CHEMISTRY, 1973, 38 (20) :3520-3524
[16]   SEMI-BENZENES DURING DIMERIZATION OF BENZYL RADICALS [J].
LANGHALS, H ;
FISCHER, H .
CHEMISCHE BERICHTE-RECUEIL, 1978, 111 (02) :543-553
[17]  
MARTEEL JP, 1975, B SOC CHIM FR II-CH, P1767
[18]  
MAUSER H, 1967, Z NATURFORSCH PT B, VB 22, P903
[20]   STEREOCHEMICAL STUDY OF HINDERED ALPHA-GLYCOLS BY H-1 AND C-13 NMR-SPECTROSCOPY [J].
PASCAL, Y ;
CONVERT, O ;
BERTHELOT, J ;
FOURNIER, F .
ORGANIC MAGNETIC RESONANCE, 1984, 22 (09) :580-585