Premium
The Photo‐Nazarov Cyclization of 1‐Cyclohexenyl(phenyl)methanone Revisited − Trapping of the 2‐Oxyallyl Intermediates by Olefins
Author(s) -
Leitich Johannes,
Heise Ingeborg,
Rust Jürgen,
Schaffner Kurt
Publication year - 2001
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 - 10.1002/1099-0690(200107)2001:14<2719::aid-ejoc2719>3.0.co;2-z
Subject(s) - chemistry , adduct , cyclooctene , cyclopentadiene , photochemistry , styrene , olefin fiber , medicinal chemistry , ene reaction , diene , stereochemistry , organic chemistry , catalysis , polymer , natural rubber , copolymer
The photochemistry (> 300 nm) of 1‐cyclohexenyl(phenyl)methanone ( 1 ) in the presence of various monoolefins and cyclopentadiene ( 9 ) has been investigated. While ( Z )‐cyclooctene and 1‐pentene were unreactive, styrene, ( E )‐cyclooctene, and diene 9 co‐reacted upon irradiation of 1 . The reactions observed include [4 + 2] and [2 + 2] cycloadditions of the monoolefins to the primary photoproduct of 1 (which is the trans isomer 2 ), and trapping reactions of the 2‐oxyallyl compound 4 formed thermally from 2 as a secondary intermediate. The trapping reactions of 4 are ene‐type additions of the olefins, analogous to those observed with the prototypical 2‐oxyallyl compound 18 in purely thermal reactions, and involving a hydrogen transfer from 4 to olefin to give adducts 10 , 12 , 13 , 24 , and 25 . However, while 18 gives one single ene‐type adduct with 9 , intermediate 4 displays two regioisomeric ene‐type addition modes with 9 , both of which are concerted, albeit nonsynchronous. In the mode resulting in 10 , it is suggested that hydrogen transfer lags behind C−C bond formation, whereas the reverse holds for the mode affording 12 and 13 . For both major adducts, 10 and 12 , concerted formation requires endo orientations of the two π systems.