Enantioselective functionalisation of the C-2' position of 1,2,3,4,5-pentamethylazaferrocene via sparteine mediated lithiation: potential new ligands for asymmetric catalysis.
The s-BuLi-sparteine base combination deprotonated the C-2' position of 1,2,3,4,5-pentamethylazaferrocene and subsequent reaction with a range of electrophiles gave C-2 substituted products in 76-93% yield and approximately 80% ee. The products could be recrystallised to enrich ee's to >90%. Resubjection of the initial addition products ( approximately 80% ee) to the deprotonation conditions led to a kinetic resolution to give products with >90% ee and superior overall yields compared to recrystallisation for the cases where the electrophiles were Ph2CO, MeI and Ph2S2. Transmetallation of the 2-lithiopentamethylazaferrocene ( approximately 80% ee) with ZnCl2 allowed palladium catalysed cross coupling with a variety of C-2 haloaryl, heteroaryl and vinyl groups to give some novel C-2' substituted pentamethylazaferrocene derivatives in 61-77% yield in 80% ee. Potential N,N-chelate ligands were recrystallised to >95% ee. A novel C2-symmetric bis-pentamethylazaferrocene could be synthesised by an iron catalysed oxidative coupling of the enatioenriched C-2 lithio derivative and in the presence of a PhMe-Et2O solvent mixture proceeded in 97% ee.
Anderson
James C
JC
School of Chemistry, University of Nottingham, Nottingham, UKNG7 2RD. j.anderson@nottingham.ac.uk
Osborne
James D
JD
Woltering
Thomas J
TJ
D002384:Catalysis; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D008094:Lithium / Q000737:chemistry*; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013034:Sparteine / Q000737:chemistry*; D013237:Stereoisomerism
C527569:1,2,3,4,5-pentamethylazaferrocene; D005296:Ferrous Compounds; D008024:Ligands; D009942:Organometallic Compounds; C434823:n-butyllithium; D013034:Sparteine; D008094:Lithium