Diesters (VII–XXIII) of retronecine (I), and acyl derivatives of the alkaloids indicine (XXIV), monocrotaline (XXVII), and retrorsine (XXIX), have been prepared for toxicological studies. Dichlororetronecine (III), is described, and also retronamine (V), an amino-analogue of retronecine, which provide a simple route to amide analogues of pyrrolizidine esters.