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Photocycloadditions of Chloranil to Homobenzvalene, Norbornadiene, and Quadricyclane
Author(s) -
Braun Max,
Christl Manfred,
Deeg Oliver,
Rudolph Marcus,
Peters EvaMaria,
Peters Karl
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199909)1999:9<2093::aid-ejoc2093>3.0.co;2-8
Subject(s) - norbornadiene , chemistry , quadricyclane , zwitterion , oxetane , photochemistry , adduct , diradical , radical ion , medicinal chemistry , chloranil , ion , polymer chemistry , catalysis , organic chemistry , molecule , singlet state , physics , nuclear physics , excited state
Solutions of chloranil ( CA ) in toluene or benzene have been irradiated in the presence of the C 7 H 8 valence isomers homobenzvalene ( HB ), norbornadiene ( N ), and quadricyclane ( Q ). In the case of HB , the adducts 3 – 6 were obtained, all of them having a rearranged structure. By a separate irradiation it was shown that 4 is a consecutive product of 3 . The structure of 4 was established by X‐ray diffraction analysis. These reactions are most probably initiated by an electron transfer (ET) from HB to 3 CA , continue by bond formation between the radical ions to give the zwitterion 14 , which undergoes Wagner–Meerwein rearrangements, and are completed by ring‐closure between the charged centres of the resulting zwitterions. The oxidation potential of N is not larger than that of HB and the products 8 – 10 may well be formed through an ET to 3 CA . However, the pathway leading to product 3 most probably involves diradical intermediates. This should also be the case for the adducts 11 and 12 , which were produced upon irradiation of methyl phenylglyoxylate ( PG ) in the presence of N . In the case of Q , an ET to 3 CA is again highly likely, followed by a combination of the radical ions to generate the zwitterion 29 , which eventually collapses to produce the oxetane 8 as the sole identifiable product. The photoreactions of CA with N and Q proceeded much less efficiently in acetonitrile solution.