Divergent Total Syntheses of Hetero-Oligomeric Iridoid Glycosides.

Divergent total syntheses of the hetero-oligomeric iridoid glycosides mainly found in Dipsacus asper were achieved. Thus, loganin ( 1 ), which is important as a monomer unit, was efficiently synthesized by stereoselective reductive cyclization using secologanin ( 2 ) as a substrate. Sequential condensation reactions of derivatives of 1 and 2 as monomer units led to the first enantioselective total syntheses of the heterooligomers cantleyoside, ( E )-aldosecologanin, dipsaperine, (3 R , 5 S )-5-carboxyvincosidic acid 22-loganin ester, and dipsanoside A.