(5R,8R,9S)-8-(tert-butyldiphenylsiloxymethyl)-9-hydroxy-9-methoxycarbonyl-1,7-dioxaspiro[4.4]non-3-ene-2,6-dione

methyl (3R)-4-tert-butyldiphenylsiloxy-3-(5-phenylthio-2-furoyloxy)-2-oxobutanoate

(5R,8R,9S,1'S)-8,9-O-(4'-methoxybenzylidene)-9-methoxycarbonyl-1,7-dioxaspiro[4.4]non-3-ene-2,6-dione

(5R,8R,9S)-8-tert-butyldiphenylsiloxymethyl-9-methoxycarbonyl-9-trimethylsiloxy-1,7-dioxaspiro[4.4]non-3-ene-2,6-dione

methyl (2R,3R)-4-(tert-butyldiphenylsilyl)oxy-2-hydroxy-3-[3-(methoxymethoxy)propionyl]oxybutanoate