Low Temperature Photolysis of<i>o</i>-Benzoquinones. Spectroscopic Detection of Cyclopentadienones and Bis-Ketenes
作者:Hideo Tomioka、Hiroshi Fukao、Yasuji Izawa
DOI:10.1246/bcsj.51.540
日期:1978.2
The photodecarbonylation of o-benzoquinone to cyclopentadienone at low temperature was monitored by infrared and ultraviolet spectra which showed that the reaction is highly sensitive to substituents. 3,5-Di-t-butyl-o-benzoquinone undergoes clean decarbonylation to give cyclopentadienone under irradiation at −170 °C. Similar irradiation of 4-t-butyl-, 4-methyl-, 3-methyl-, and unsubstituted o-benzoquinones also leads to decarbonylation to cyclopentadienones. However, competitive α-cleavage to bis-ketene becomes important in these systems. Direct spectroscopic observation of the elusive cyclopentadienone was unsuccessful because of the overlapping absorption of the by-product. The infrared spectrum of bis-ketene from 4-t-butyl-o-benzoquinone shows that it exists as a mixture of rotamers, not undergoing thermal interconversion even at −170 °C.
通过红外和紫外光谱监测了邻苯醌在低温下光脱羰生成环戊二烯酮的过程,结果表明该反应对取代基高度敏感。 3,5-二叔丁基邻苯醌在-170 °C 照射下进行清洁脱羰得到环戊二烯酮。 4-叔丁基-、4-甲基-、3-甲基-和未取代的邻苯醌的类似照射也会导致脱羰生成环戊二烯酮。然而,在这些系统中,竞争性 α-裂解为双烯酮变得很重要。由于副产物的重叠吸收,对难以捉摸的环戊二烯酮的直接光谱观察并不成功。 4-叔丁基邻苯醌的双乙烯酮的红外光谱表明,它以旋转异构体的混合物形式存在,即使在-170℃下也不会发生热互变。