A method for the synthesis of octalactin B is established via a new and quite effective mixed-anhydride lactonization for the synthesis of an eight-membered ring moiety using 2-methyl-6-nitrobenzoic anhydride with DMAP. Both an optically active linear precursor of the lactone and a sidechain of octalactins are prepared by the enantioselective aldol reaction of ketene silyl acetals with aldehydes.
synthesized in a direct, and efficient manner. Lactone 1 was made using a substrate controlled lactonization reaction using the carbodiimide EDCI and two crotylborane additions were used to access the precursor hydroxyacid. The importance of proper substitution in the hydroxyacid tether is noted for successful medium-ring lactonization. Synthesis of the sidechain vinyl iodide 2 employed an asymmetric allenylboronate