The ortho metallation of some aromatic ring systems has been investigated in regard to the influence of several types of phosphorus-centred directing groups upon the reactivity, regioselectivity, and utility in later synthetic elaboration. The metallation step allows derivatisation in several useful ways, offering several routes to the synthesis of novel chiral ditertiary phosphines. Thus, an ortho lithiation of N,N,N',N'-tetramethyl-P-phenylphosphonic diamide (10) led to the interesting primary phosphine, 2-(diphenylphosphino)phenylphosphine (14), after elaboration of the phosphonic diamide directing group. This primary phosphine undergoes an unprecedented facile phenyl group exchange process between its two phosphorus atoms, upon di-lithiation of the primary phosphorus centre. The primary phosphorus centre of (14) has been elaborated in several ways to yield new ditertiary phosphines. The alkylation of this centre in the copper(I) chelate complex has been investigated in several directions. In another direction, (14) has been chemically elaborated to give a new hybrid chiral ditertiary phosphine ligand, "SemiPHOS", containing both a chiral phospholane ring and an adjacent diphenylphosphino group. SemiPHOS has been obtained in optically pure forms by a stereoselective synthesis and, independently, by a resolution procedure on its racemate. The molecular design of SemiPHOS was devised such that, when chelated to a metal atom, a subtle steric interaction appears to allow the chirality of the phospholane ring to influence the neighbouring diphenylphosphino group to adopt a complementary chiral conformation. This idea was tested and evaluated by applying SemiPHOS in catalytic asymmetric hydrogenations of (Z)-a-(Nacylamino) acrylate substrates to produce the R-amino acid precursors. Aryl species lithiated ortho to phosphorus-centred directing groups were coupled oxidatively by a convenient in situ method, to yield biaryl species that could then be elaborated to give biaryl ditertiary phosphine ligands. This method was used to make several atropisomeric chiral ditertiary phosphines.
| Identifer | oai:union.ndltd.org:ADTP/187868 |
| Date | January 1999 |
| Creators | Lin, Qinghong, Chemistry, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Chemistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Qinghong Lin, http://unsworks.unsw.edu.au/copyright |
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