THE SYNTHESIS AND ABSOLUTE-CONFIGURATION OF THE NOVEL ICHTHYOTOXIC DIACYLGLYCEROLS, UMBRACULUMIN-A AND UMBRACULUMIN-C

The total syntheses of umbraculumin A 1 and umbraculumin C 2 in homochiral form are described. Noteworthy steps involve (i) the preparation of the key Z,E-acid 10 by organolithium addition to pyrylium salts, (ii) the use of the 4-methoxyphenylmethyl protecting group for the preparation of 1,2-diacyl glycerols and its removal using trifluoroacetic acid-anisole without significant acyl migration (DDQ removal having proved inefficient) and (iii) a new procedure for the stereoselective preparation of (Z)- and (E)-3-methylthiopropenoic acid.