Abstract
Enantiomerically pure 2-hydroxyalkyl, 2-aminoalkyl and 2-iminoalkyl ferrocenyl p-tolylsulfides are easily prepared in good yields and with complete diastereocontrol from (S)-(2-p- tolylthio)ferrocencarboxyaldehyde. This aldehyde provides also an easy access to the first enantiomerically pure planar chiral ferrocenyl cyanohydrin. The absolute configuration of the new stereocenters has been determined by single-crystal X-ray analysis.
Highlights
The design and the synthesis of new ferrocenyl derivatives possessing planar and/or central chirality are of great importance in the development of new versatile and effective ligands as well as of useful chiral auxiliaries and building blocks[1] for asymmetric synthesis
1,2-Disubstituted enantiomerically pure planar chiral ferrocenylaldehydes have been recently employed as precursors of more complex molecules,[17] in particular the formyl group could be stereoselectively alkylated[18] by reaction with organometallic reagents
In particular chiral ferrocenyl amines possessing central chirality have been obtained via highly stereoselective additions of organolithium[20] or organozinc[21] reagents to chiral ferrocenyl imines deriving from enantiomerically pure amines or by enantioselective addition of dialkylzinc reagents to achiral ferrocenyl imines in the presence of chiral ligands.[22]
Summary
The design and the synthesis of new ferrocenyl derivatives possessing planar and/or central chirality are of great importance in the development of new versatile and effective ligands as well as of useful chiral auxiliaries and building blocks[1] for asymmetric synthesis. As a part of our ongoing interest in sulfur containing compounds[24] and in molecules bearing the sulfur and the ferrocene moiety,[25] we have recently synthesized enantiomerically pure βhydroxyalkyl, β-aminoalkyl and β-iminoalkyl ferrocenyl sulfides having only the central chirality. Some of these derivatives were successfully employed as ligands in palladiumcatalyzed allylic substitution with asymmetric induction up to 99%.26. The enantiomerically pure 4 can react with organometallic reagents affording 1 and with amines allowing the preparation of ferrocenyl imines 3, which in turn may be converted into 2 by reaction with organometallic reagents introducing a new stereogenic center beside the planar chirality
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