The Diels-Alder adduct of 2,4-dimethylfuran to 1-cyanovinyl (1'S)-camphanate was converted into (2R,3R,4S,5S,6R,7R)-3,6-epoxy-4,5-isopropylidenedioxy-2,4,6-trimethyl-7- [(tert-butyl)-dimethylsilyloxy]non-1-yl phenyl sulfoxides (6), the condensation of which with (3R,4S,5R,6S)-7-benzyloxy-3,5-isopropylidenedioxy-4,6-dimethylheptan-2-o ne (7) led to the partially-protected seco-acid of the 9,12-anhydroerythronolide aglycon (5). (C) 1998 Elsevier Science Ltd. All rights reserved.