Enantioselective Synthesis of Carbohydrate Precursors via 1,2:2,3-Bis-Epoxide Intermediates

Article abstract of DOI:10.1021/jo00085a038

Bis-epoxidation of the DPS-substituted allenylcarbinyl acetates 9, 13, 19, 22, and 30 afforded the enones 10, 36, 20, 23, and 31, respectively, in 80-90percent yield with excellent stereoselectivity.Treatment with DBU effected C to O DPS transfer leading to the methyl-branched hexose precursors, enones 11, 37, 21, and 24.The higher homologue 33 gave the branched 7-deoxyheptose precursor 33.Reduction of enones 11, 37, and 33 with NaBH4-CeCl3 yielded the α-(S) alcohols 12, 38, and 35 in high yield.Alcohol 38 was converted to the 1-deoxy-4-methylpyranose tetraacetate 48 by epoxidation, base treatment, desilylation, and acetylation.An acyclic analogue of 48, acetonide 53, could be prepared from epoxide 39 by treatment with PhSH and NaOH, followed by silyl ether cleavage, acetonide formation, and Pummerer rearrangement-reduction.On the other hand, hydroxylation of alcohol 38 with OsO4-NMO led to the selectively protected branched hexitol 59, with high diastereoselectivity.The allylic alcohol benzoate 63 was likewise converted to diol 64.