TEMPORARY SULFUR CONNECTION IN AN INTRAMOLECULAR S(N)2 REACTION - A STEREOCONTROLLED SYNTHESIS OF (+ -)-KAINIC ACID/

Homolytic isomerization of isocyanide 7 affords 2 beta-t-butoxycarbony l-3 beta-(t-butyldimethylsilyloxy)-4 lpha-isopropenyl-5-ethylthio-4H-2 ,3-dihydropyrrole (8). The conversion of key intermediate 8 into (+/-) -kainic acid (3) involves, inter alia, temporary sulfur connection of an acetic acid moiety to the chiral isopropylene anchor, followed by i ts regio- and stereospecific intramolecular bonding to the pyrrolidine backbone. The acetic acid moiety is eventually disconnected from its anchor with concomitant regeneration of the isopropylene group by a ne w samarium(II) iodide-mediated tandem reductive elimination.