Über die absolute Konfiguration der Cantharsäure und des Palasonins

The absolute configurations of (+)‐cantharic acid, a chiral derivative of the achiral insect defensive substance cantharidin ( 1 ), and of palasonin, a lower homologue of 1 occurring in the plant Butea frondosa , were shown to be represented by formulas 2 and 3 , respectively ( scheme 1 ). These results were obtained by application of the Horeau method ( table 1 ) on the (+)‐cantharic acid derivatives (+)‐ 5 , (−)‐ 7 , and (−) 11 ( scheme 2 ), and the palasonin derivatives (+)‐ 29 and (+)‐ 30 ( scheme 4 ), as well as by comparison of the chiroptical properties ( tables 2 and 3 ) of a number of derivatives, prepared from either cantharic acid or palasonin. – Attempts to incorporate various radioactively labelled precursors into palasonin ( 3 ), using young and adult plants, have been so far unsuccessful.