Planar Chiral Ferrocene Lithium Amide Bases: A New Generation of Bases for Asymmetric Synthesis
Publication Date
December 13, 2002
Creator
Abstract
The design and preparation of a new class of planar chiral ferrocenyl lithium amide bases is described. Work commenced on preparing N./V-dimethyl-l-ferrocenylethylamine derivatives. Electrophilic amination was attempted with a variety of reagents, but no diamines were ever obtained. The introduction of a boronic acid group was also attempted, but no products were isolated. Finally, nitration followed by reduction was investigated, but again proved unsuccessful, resulting only in the preparation of a dimer of the starting amine, 2,2'-bis-[ 1 -(//, A-dimethylamino)-ethyl]-l, l'-biferrocenyl.
Our attention turned to derivatives of MN-diisopropylferrocene carboxamide. Metallation, followed by quenching with iodine gave Af,N-diisopropyl-2- iodoferrocene carboxamide. Copper(I) oxide mediated coupling of the iodide with either acetic acid or phthalimide gave access to ortho-oxygen and nitrogen donor groups. A new class of planar chiral bases (N-alkyl-(2- alkoxyferrocenyl)methylamines) were prepared from this starting material by reduction of the amide, followed by substitution of the diisopropylamine with a range of primary amines.
Assays were carried out using the deprotonation of 4-tert-butylcyclohexanone and trapping of resultant enolate with TMSC1. Bases having a plane of chirality as the only stereochemical element, disappointingly, gave nearly racemic silyl enol ether, however low optical purities were recorded for bases consisting of both central and planar chirality. A non-chelating planar chiral lithium amide base was prepared (^S}-A^-rer/-butyl-(2-methylfen'ocenyl)-t methylamine, however this too gave nearly racemic silyl enol ether in the assay reaction.
The synthesis of planar chiral azaferrocenyl bases was attempted by sequential complexation of lithiated pyrrole-2-methanol and lithium pentamethyl- cyclopentadienide with iron(II) chloride, followed by acylation of the pendant alcohol. However, all attempts to substitute the acetate with an amine proved unsuccessful.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Chemistry
eprints ID
59224
UoN Repository URI
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