Intramolecular Photoreactions of 9‑Cyanophenanthrene-Linked Arylcyclopropanes

With
the aim of developing efficient and useful processes for the
preparation of polycyclic organic compounds, intramolecular [3 + 2]
photoreactions of 9-cyanophenanthrene-linked arylcyclopropanes were
investigated. Photoreactions of 6a,b, which contain respective p-methoxyphenylcyclopropane and phenylcyclopropane moieties,
form the intramolecular [3 + 2] photocycloadducts, endo- and exo-7a,b, along with the dihydroisochroman derivatives, cis- and
trans-8a,b. The efficiency of the photoreaction of 6a is higher when benzene rather than acetonitrile is used
as a solvent. Interestingly, this solvent effect is reversed in the
photoreaction of 6b, where the efficiency is higher in
acetonitrile than that in benzene. On the basis of the observed effects
of substituents and solvents, fluorescence emission from intramolecular
exciplexes, and ΔGs for intramolecular single
electron transfer (SET), we propose that the photoreactions proceed
through pathways involving the initial formation of singlet intramolecular
exciplexes and/or SET between the excited 9-cyanophenanthrene and
the ground-state arylcyclopropane moieties.

本研究以开发高效实用的多环有机化合物制备方法为目标，对9-氰菲连接的芳基环丙烷类化合物的分子内[3+2]光化学反应展开了探究。底物6a和6b分别带有对甲氧基苯基环丙烷与苯基环丙烷结构单元，其光反应可生成分子内[3+2]光环加成产物内型-7a、外型-7a以及内型-7b、外型-7b，同时伴随二氢异色满衍生物顺式-8a、反式-8a和顺式-8b、反式-8b的生成。以苯为溶剂时，底物6a的光反应效率高于乙腈溶剂体系；而有趣的是，该溶剂效应在底物6b的光反应中恰好相反：乙腈中的反应效率优于苯溶剂。基于观测到的取代基与溶剂效应、分子内激基复合物的荧光发射行为，以及分子内单电子转移（Single Electron Transfer, SET）的吉布斯自由能变（ΔGs），我们提出该类光反应通过以下路径进行：首先在激发态9-氰菲与基态芳基环丙烷结构单元之间形成单重态分子内激基复合物，或发生单电子转移过程。