Cyclobutene photochemistry. Adiabatic photochemical ring opening of alkylcyclobutenes

被引:6
作者
Leigh, WJ
Postigo, JA
Zheng, KC
机构
[1] Department of Chemistry, McMaster University, Hamilton
来源
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE | 1996年 / 74卷 / 06期
关键词
photochemistry; cyclobutene; electrocyclic; adiabatic; conical intersection; orbital symmetry;
D O I
10.1139/v96-105
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The photochemistry of the cis and trans isomers of a series of dimethylbicyclo[n.2.0]alk-(n+2)-enes (n = 2-5) (bicyclic cyclobutene derivatives in which the C=C bond is shared by the two rings) in pentane solution is described. Irradiation of these compounds using monochromatic 193- or 214-nm light sources results in ring opening to yield the corresponding 1,2-bis(1-ethylidene)cycloalkanes (C-4-C-7) in high chemical and quantum yields. In all cases, the reaction proceeds with a high (70-90%) degree of disrotatory stereoselectivity. Quantum yields for direct cis,trans photoisomerization of the isomeric E,E- and E,Z-1,2-bis(1-ethylidene)cycloalkanes have also been determined. The product distributions from irradiation of the cyclobutenes are wavelength dependent, but for 214-nm excitation the isomeric diene distributions obtained from cyclobutene ring opening agree fairly closely with those calculated from the quantum yields for cis, trans photoisomerization of the isomeric dienes on the assumption that the process involves purely disrotatory ring opening to yield a single diene isomer in the lowest excited singlet state. The results are consistent with an orbital-symmetry-controlled, adiabatic mechanism for ring opening.
引用
收藏
页码:951 / 964
页数:14
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