The Crystal Structure of 1,2-Didehydrocrotalanine Picrate: A Macrocyclic Pyrrolizidine Alkaloid Analogue

1,2-Didehydrocrotalanine ( 2 ) is the first synthetic macrocyclic pyrrolizidine alkaloid analogue to be studied by X-ray crystallography. The crystal structure was solved by multisolution direct methods and refined by full-matrix least-squares to R = 0.036 for 693 reflections. The alkaloid analogue has an 11-membered macrocycle containing two ester groups with their carbonyl groups nearly antiparallel.