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Issue 2, 2008
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Enantioselective functionalisation of the C-2′ position of 1,2,3,4,5-pentamethylazaferroceneviasparteine mediated lithiation: potential new ligands for asymmetric catalysis

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Abstract

The s-BuLi–sparteine base combination deprotonated the C-2′ position of 1,2,3,4,5-pentamethylazaferrocene1 and subsequent reaction with a range of electrophiles gave C-2 substituted products in 76–93% yield and ∼80% ee. The products could be recrystallised to enrich ee's to >90%. Resubjection of the initial addition products (∼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 (∼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 10 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.

Graphical abstract: Enantioselective functionalisation of the C-2′ position of 1,2,3,4,5-pentamethylazaferroceneviasparteine mediated lithiation: potential new ligands for asymmetric catalysis

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Publication details

The article was received on 05 Oct 2007, accepted on 06 Nov 2007, published on 29 Nov 2007 and first published online on 29 Nov 2007


Article type: Paper
DOI: 10.1039/B715323F
Citation: Org. Biomol. Chem., 2008,6, 330-339
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    Enantioselective functionalisation of the C-2′ position of 1,2,3,4,5-pentamethylazaferroceneviasparteine mediated lithiation: potential new ligands for asymmetric catalysis

    J. C. Anderson, J. D. Osborne and T. J. Woltering, Org. Biomol. Chem., 2008, 6, 330
    DOI: 10.1039/B715323F

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