ASCENT OF THE ALDOSE SERIES BY 4 CARBON-ATOMS - TOTAL SYNTHESIS OF D-GLYCERO-D-TALO-L-TALO-UNDECOSE PENTAACETONIDE

Enantiomerically pure undecose acetonide 9 was synthesized, through heptose intermediate 5, starting with D-glyceraldehyde acetonide (1). The key steps were two consecutive four-carbon homologations, each consisting of four reactions: (i) stereoselective elongation of the aldehyde precursor with 2-(trimethylsiloxy)furan, giving C(n+4) butenolide templates 2 and 6, (ii) anti-selective cis-dihydroxylation of the butenolide double bond, giving fully functionalized lactones 3 and 7, (iii) lactone ring opening and protection, giving open-chain methyl esters 4 and 8, and (iv) DIBAL reduction to aldoses 5 and 9. At the end of the eight-step sequence, undecose 9 was prepared in a 5.1% overall yield, which corresponded to a 69.5% average yield per step.