Abstract
Two dibenzobarrelene derivatives were synthesized that are covalently
linked to a (S)-BINOL unit through an oxymethylene (1b) or
ethylenedioxymethylene (1c) unit, and their photoreactivity
was examined. Irradiation of 1b in acetone resulted in
a di-π-methane rearrangement to give diastereoselectively one
dibenzosemibullvalene isomer. Experimental and theoretical data point
to a directing effect of the BINOL auxiliary based on steric
repulsion. The derivative 1c with a longer linker between the
BINOL unit and the dibenzobarrelene is photoinert, presumably because
of fast competing relaxation processes in the excited state.
摘要:合成了两种二苯并[4,5]环戊二烯衍生物,它们通过氧亚甲基(1b)或乙二醇亚甲基(1c)单元与(S)-BINOL单元共价连接,并研究了它们的光反应性。在丙酮中照射1b导致二π-甲烷重排反应,选择地形成了一个二苯并半牛烯异构体。实验和理论数据表明,基于立体排斥,BINOL辅助剂具有定向作用。具有较长连接剂的1c衍生物在光激发态中是光惰性的,可能是因为存在竞争性的快速弛豫过程。