Trienes in which the requisite 1,3-diene and allylic ether moieties are appended to a pre-existing ring system afford bicyclic ring systems upon iron-catalyzed cyclization. The efficiency and stereoselectivity of the cyclization are dramatically influenced by the nature of the ring system to which the diene and alkene subunits are appended. Certain bicyclic ring systems are formed in good yield; most notably, substrates bearing a basic nitrogen are well-tolerated and certain indolizidine and quinolizidine ring systems are accessible using this methodology. The efficiency and stereoselectivity of the cyclization is also markedly dependent on the ligand used to modify the iron catalyst, and in this regard, a bisoxazoline-modified iron catalyst system is generally superior to what was the standard bipyridine-modified catalyst. In the course of these studies a difference spin polarization transfer (DSPT) experiment proved very useful for the stereochemical analysis of compounds that exhibit very crowded high field NMR spectra.
ASJC Scopus subject areas
- Organic Chemistry