Synthesis of Cycloprodigiosin Identifies the Natural Isolate as a Scalemic Mixture
摘要:
The enantiomers of the natural product cycloprodigiosin were prepared using an expedient five-step synthetic sequence that takes advantage of a Schollkopf-Barton-Zard (SBZ) pyrrole annulation with a chiral isocyanoacetate and a nitrocyclohexene derivative. Using chiral HPLC and X-ray crystallographic analyses of the synthetically prepared Material and natural isolate (isolated from the marine bacterium Pseudoalteromonas rubra), naturally occurring cyclo-prodigiosin was determined to be a scalemic mixture occurring in an enantiomeric ratio of 83:17 (R)/(S) at C4'.
Enantioselective Synthesis: Steric and electronic effects of the substrates upon stereoselectivity in the gold(I)-catalyzed aldol reaction with chiral ferrocenylamine ligands, preliminary communication
作者:Antonio Togni、Stephen D. Pastor
DOI:10.1002/hlca.19890720521
日期:1989.8.9
Enantioselectivity in the gold(I)-catalyzed aldol reaction with chiral ferrocenylamine ligands is strongly dependent upon both the steric and electronic effects of the substrates. In the reaction of pyridine-2-, 3-, and 4-carbaldehydes with ethyl 2-isocyanoacetate, surprisingly and significantly different enantioselectivities were observed in the formation of the cis- and trans-dihydro-oxazoles that