Stereocontrolled ring-opening of some enantiomerically enriched epoxy ketones and epoxy alcohols using trimethylaluminium: synthesis of (S )-2-arylpropanoic acids

Poly-(D)-leucine-catalysed epoxidation of chalcone furnished epoxide (+)-6; treatment of this epoxide with trimethylaluminium followed by zinc borohydride reduction and oxidative cleavage furnished (S)-2-phenylpropanoic acid 11. In a complementary sequence epoxy ketones (−)-6 and 25 were converted into (S)-2-phenylpropanoic acid and (S)-fenoprofen 5 respectively by reduction with zinc borohydride, reaction with trimethylaluminium and oxidative cleavage. Similarly epoxy ketones (−)-6, 21 and 28 were treated with methylmagnesium iodide, trimethylaluminium and the resultant alcohols subjected to oxidative cleavage to afford (S)-2-phenylpropanoic acid (from the first two substrates) and (S)-naproxen 1.