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

• Published in: European Journal of Organic Chemistry Vol. 2011; no. 5; pp. 968 - 982
• Main Authors: Christl, Manfred, Braun, Max, Deeg, Oliver, Wolff, Stephan
• Format: Book Review Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.02.2011; WILEY‐VCH Verlag; Wiley; Wiley-VCH
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Chemistry, Organic; Cycloaddition; Dechlorination; Endiones; Exact sciences and technology; General and physical chemistry; Noncondensed benzenic compounds; Organic chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Physical Sciences; Polycycles; Preparations and properties; Science & Technology; OXIDATION; Cycloaddition; Dechlorination; ELECTRON-TRANSFER; QUINONES; Endiones; PHOTOINDUCED REACTIONS; Polycycles; Photochemistry; PHOTOELECTRON-SPECTROSCOPY; Four membered ring; Quinone; Benzoquinone derivatives; Benzene derivatives; Asymmetric molecule; Polycyclic compound; Photochemical reaction; Ketone; Chemical reduction; Ultraviolet radiation; All cis stereoisomer; Bulb; Cyclobutane derivatives; Chloranil; Benzenic compound
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201001304

Depending on the reaction conditions, excited chloranil (3CA) 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, 3CA 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 cycloadduct that resulted from 3CA and cis‐CO in addition to two symmetrical 1:2 cycloadducts. Also, excited 11a and cyclohexene (CH) furnished a bis(cyclobutane) derivative, a significant portion of which was subject to a dechlorination to give a cyclobutene derivative. cis,cis‐1,5‐Cyclooctadiene (COD) and CH were transformed by 3CA to 1:1 and 1:2 cycloadducts, analogous to cis‐ and trans‐CO. In addition to this, 3CA suffered photoreduction in the presence of COD and CH. The [2+2] cycloaddition onto a carbonyl group of 3CA with formation of a spirooxetane occurred to a small extent only with COD, but not at all with cis‐ and trans‐CO and CH. At variance with a previous report, which claimed the formation of a spirooxetane, the photoreaction of chloranil with cis‐cyclooctene is shown to give a cyclobutane derivative in good yield with a high stereoselectivity.