Quick access to polyfunctional spiroketal (3R)-4-[(2S,6R,8R, 10S)-4,4-bis(ethylthio)-10-hydroxy-8-(2-hydroxyethyl)- 1,7-dioxaspiro[5.5]undec-2-yl]butane- 1,3-diol [(+)-19] is now available through the stereoselective functionalization of enantiomerically pure protected tetrol (4R,4'R,6R,6'R)- 1, l'-methylenebis[4-[(benzyloxy)methoxy]-6-[(triethylsilyl)-oxy]cyclohept- 1-ene [(-)-9], derived from 2,2'-methylenedifuran. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).