Michael addition of (-)-(1S,5R,6R,7S)-6,7-bis(methoxymethoxy)-2,8-dioxabicyclo[3.2.1]-octan- 3-one lithium enolate to (+)-(1R,4S,5S,6S)-5-benzeneselenyl-6-chloro-3-methylidene-7-oxabicyclo[2 .2.1]heptan-2-one gives a single adduct with highstereoselectivity. it was converted into a derivative of beta-D-(1-->3)-C-linked 1,5-dideoxy-1,5-imino-lyxopyranoside of alpha-D-mannofuranurono-6,1-lactone and other long-chain, branched sugars.