Asymmetric synthesis of (-)-7-epiaustraline and (+)-1,7-diepiaustraline.

A diastereoselective and modular approach to the synthesis of the 3-hydroxymethyl-2,3,5,6,7,7a-hexahydro-1H-pyrrolizine-1,2,7-triol structure, characteristic of several natural pyrrolizidine natural products, has been developed. This approach culminated in the synthesis of (-)-7-epiaustraline and (+)-1,7-diepiaustraline. The oxazolidinone group has been found to be a useful protecting group in the RCM reaction and, as part of a pyrrolo[1,2-c]oxazol-3-one ring system, has functioned as a stereo- and regio-directing group in a key diastereoselective cis-dihydroxylation reaction and a regioselective nucleophilic ring-opening of a S,S-dioxo-dioxathiole.