Creation of quaternary stereocentres: synthesis of new polyhydroxylated indolizidines

(6R,7S,8aR)- and (6S,7R,8aR)-8a-tert-butyldimethylsilyloxymethyl-6,7-dihydroxy-indolizidin-3-ones 14 and 15 were synthesized from bicyclic silyloxypyrrole 2 by the selective formation of a quaternary stereogenic centre and a ring-closing metathesis as the main steps. They were converted into new polyhydroxyindolizidines 20 and 21 with high diastereoselectivity.