Regio- and diastereoselective ene reactions of singlet oxygen with dialkyl-substituted acrylic esters

✍ Scribed by Adam, Waldemar ;Nestler, Bernd

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 319 KB
• Volume: 1990
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1990199001190

✦ Synopsis

Abstract

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.