Photochemical Reactions of Chloranil with Cyclooctene, 1,5‐Cyclooctadiene, and Cyclohexene Revisited

Abstract

Depending on the reaction conditions, excited chloranil ( 3 CA) and cis-cyclooctene (cis-CO) furnished three types of products, which all contain carbocyclic four-membered rings. The illumination of a solution in benzene by light bulbs gave rise to the all-cis 1:1 cycloadduct (11a) in 76 % yield. On its part, this compound reacted with cis-CO under the action of better sources for UV light with the formation of three isomeric 1:2 cycloadducts. Two of them underwent a photochemical dechlorination leading to a cyclobutene derivative. Albeit rather sluggishly, 3 CA and trans-cyclooctene (trans-CO) brought about an unsymmetrical 1:1 and a 1:2 cycloadduct. By contrast, excited 11a reacted smoothly with trans-CO and afforded a 72 % yield of the unsymmetrical 1:2 cy-

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…421 The reaction of chloranil (220) with several olefins can be successfully conducted as a monoaddition reaction if the irradiation wavelength is properly chosen. Christl and co-workers 422,423 isolated the intermolecular [2 + 2] photocycloaddition product 221 of cyclooctene when visible light was employed for excitation (Scheme 69). Irradiation at a shorter wavelength led to multiple addition and other side reactions.…”

General Synthetic Approach to Diverse Taxane Cores

“…Notably, visible light-induced [2 + 2] photocycloadditions are usually facilitated by an additive, such as a photocatalyst . This work, however, serves as a rare example of a [2 + 2] cycloaddition proceeding readily under just blue LED irradiation without any special additives . To the best of our knowledge, this report also provides the first experimental evidence supporting the plausibility of this key biosynthetic step…”

Photoinduced Reactions ofpara-Quinones with Bicyclopropylidene Leading to Diverse Polycyclic Compounds with Spirocyclopropanes

“…It was reported that product distribution of photoreactions between p -quinones and olefins was mainly dependent on the nature of the excited state of quinones (nπ* or ππ* triplet state) . Meanwhile, the involvement of photoinduced electron transfer (PET) process and steric effect to the cycloaddition also play important roles and may cause a reaction site reversal. ,, To examine the possibility of PET process involvement in the photoreactions between p -quinones and BCP, free energy change for electron transfer (Δ G ET ) between the triplet quinone and BCP has been evaluated using the Weller equation (Table ). The results showed that the PET process with BCP to all the quinones investigated was endergonic and it was unlikely to be involved in the photoreactions.…”