The intermediates 3 and 4, useful in the preparation of new biologically active bafilomycin derivatives, were obtained via a thermal retro-aldol reaction in diphenyl ether. The starting materials 5 and 7 for the retro-aldol reaction were synthesized in a few steps from bafilomycin C-1 (2) with or without a protective group at 7-OH. (C) 1999 Elsevier Science Ltd. All rights reserved.