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Regio‐ and diastereoselective ene reactions of singlet oxygen with dialkyl‐substituted acrylic esters
Author(s) -
Adam Waldemar,
Nestler Bernd
Publication year - 1990
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.1990199001190
Subject(s) - photooxygenation , allylic rearrangement , chemistry , ene reaction , diastereomer , singlet oxygen , triphenylphosphine , medicinal chemistry , stereocenter , singlet state , oxygen , catalysis , stereochemistry , organic chemistry , enantioselective synthesis , physics , nuclear physics , excited state
Photooxygenation of methyl ( E )‐ and ( Z )‐2‐methyl‐4‐phenyl‐2‐pentenecarboxylates ( E ‐ 1 , Z ‐ 1 ) afforded the hydroperoxy esters ( R *, S *)‐ 2a and ( S *, S *)‐ 2b through regiospecific and diastereo‐selective ene reaction of singlet oxygen at the α‐methyl group with a diastereomeric ratio (d.r.) of 2a:2b ca. 80:20 for E ‐ 1 and ca. 65:35 for Z ‐ 1 . The relative configurations of 2a , b were established by chemical correlation through triphenylphosphine reduction of the allylic hydroperoxy esters 2a , b to the allylic hydroxy esters 4a , b and subsequent catalytic hydrogenation to the literature‐known saturated hydroxy esters 5a , b (from pure 4a ) and 5c , d (from pure 4b ). The appreciable diastereoselectivity (d.r. ca. 80:20) observed for the E ‐ 1 isomer is explained in terms of the cis effect, by coordinating the allylic hydrogen of the stereogenic C‐4 position to the terminal oxygen of the postulated perepoxide‐like structure.