Enantioselective synthesis of (+)-shikimic acid and (+)-5-epi-shikimic acid by asymmetric Diels-Alder reaction of (S)-α-sulfinylacrylates

Abstract Enantiopure ( S ) benzyl and t -butyl 2- p -tolysulfinylpropenoates ( 1 and 2 ) were readily prepared by Mannich condensation of ( R p -tolysulfinylacetates (Ch 2 O+Me 2 NH), followed by in situ nitrogen quaternization. These new chiral dienophiles reacted with furan at high pressures (4–13 Kbar) at rt to afford maily a 2:1 mixture of both endo adducts (itendo- B + endo - A ). Enantiopure endo - 4B and endo - 4A were stereoselectively transformed into (+)-shikimic acid and (+)-5- epi -shikimic acid respectively, by dihydroxylation of the double bond, removal of the sulfinyl group, basic opening of the oxabicyclic skeleton and hydrolysis of the ester moiety.