Mixed bidentate ligands: The first chiral phosphonite-phosphite

Article abstract of DOI:10.1016/S0040-4039(00)00386-5

The chiral bidentate phosphonite-phosphite ligand (R)-4-((R)-2- naphtho[1,2-f]naphtho[2,1-d]1,3,2-dioxaphosphepin-4-ylphenoxy)naphtho[1,2- f]naphtho[2,1-d]1,3,2-dioxaphosphepin is accessible in three simple steps starting from o-bromophenol. (C) 2000 Else

Full text of DOI:10.1016/S0040-4039(00)00386-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 3315–3317
Mixed bidentate ligands: the first chiral phosphonite-phosphite
Manfred T. Reetz ∗ and Mireia Pastó
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim/ Ruhr, Germany
Received 22 February 2000; accepted 29 February 2000
Abstract
The chiral bidentate phosphonite-phosphite ligand (R)-4-((R)-2-naphtho[1,2-f]naphtho[2,1-d]1,3,2-
dioxaphosphepin-4-ylphenoxy)naphtho[1,2-f]naphtho[2,1-d]1,3,2-dioxaphosphepin is accessible in three
simple steps starting from o-bromophenol. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: phosphonic acids and derivatives; phosphorous acid and derivatives; rhodium and compounds; catalysis.
A number of chiral mixed bidentate ligands have been prepared for asymmetric transition metal
catalyzed reactions, such classes of compounds as phosphines, phosphinites, phosphonites, phosphites
as well as nitrogen-based functionalities serving as the donor moieties in the ligands.1–9 Oddly enough,
the combination of a phosphonite RP(OR0)2 and a phosphite P(OR)3 has never been considered. Here we
report the first synthesis of such a chiral bidentate ligand.
A wide variety of chiral compounds encompassing phosphonite and phosphite functionalities can
be envisioned. We decided to choose an achiral backbone and chiral P-based heterocycles as the two
different donor moieties, as in the phosphonite-phosphite 1 which can potentially form six-membered
chelates with appropriate transition metals.
In our first attempt to prepare 1, the dilithio intermediate 3 was quenched with two equivalents of
(R)-dinaphthylphosphorochloridite (Scheme 1). Since a difficult to separate mixture of products was
∗
Corresponding author. Tel: +49 208 306 2000; fax: +49 208 306 2985; e-mail: reetz@mpi-muelheim.mpg.de (M. T. Reetz)
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00386-5
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observed, an alternative route was chosen based on the known compound 4.10 Treatment with dry HCl
afforded the new compound 5 which was isolated as an oil in 75% yield.† Reaction with (R)-dinaphthol
in the presence of triethylamine provided the desired ligand 1 with good conversion. Separation from the
amine hydrochloride resulted in some material loss, but compound 1 could be isolated in 40% yield.‡
Scheme 1.
The ligand 1 was then treated with Rh(cod)2BF4 under standard conditions to afford 1–Rh(cod)BF4 as
a yellow-orange powder (64% yield; 31P NMR (121.5 MHz, CD2Cl2: δ 158.3 (dd, JRhP=199 Hz, 4J=70
Hz, 132.1 (dd, JRhP=264 Hz, 4JPP=69 Hz).
In summary, we have prepared in a simple manner the first chiral bidentate ligand (1) encompassing
phosphonite-phosphite moieties, as well as its Rh-complex 1–Rh(cod)BF4. Work is in progress to test
the catalyst selectivity of 1–Rh(cod)BF4§ and of other metal complexes derived from ligand 1 or of other
chiral phosphonite-phosphite ligands.
Acknowledgements
Mireia Pastó thanks the Ministerio de Educacion y Cultura (Spain) for a postdoctoral fellowship.
References
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†
Synthesis of 5: A solution 4 (0.19 g; 0.43 mmol) in 3 mL of diethyl ether was treated with 0.62 mL (3.5 mmol) of a 5.6 M
solution of HCl in ether under an Ar atmosphere at −70°C. Precipitation of NEt2H2Cl occurred immediately to give a pasty
suspension which was diluted with 2 mL of ether, and stirring was continued for 3.5 h. The precipitate was filtered through Celite
and the solvent evaporated under reduced pressure, yielding 95 mg (75%) of an oil that was used without further purification.
31P NMR (121.5 MHz, CDCl3): δ 183.1 (d, J=13 Hz), 153.8 (d, J=13 Hz).
‡
Synthesis of 1: (R)-Dinaphthol (0.3 g; 1.1 mmol) in 17 mL of ether was added slowly at −70°C within 1 h to a mixture of
5 (0.54 mmol) and NEt3 (0.61 mL, 4.4 mmol) in 2 mL ether. After stirring overnight with warming to room temperature the
suspension was filtered over Celite and the solvent removed. The crude solid (0.22 g) contained some amine hydrochloride and
was suspended in CH2Cl2:pentane (1:1). After filtration the solvent was stripped of yielding 0.12 g (30% from 4) of 1. 31P NMR
(121.5 MHz, CD2Cl2): δ 177.4 (d, 4JPP=13 Hz), 144.1 (d, 4JPP=14 Hz).
§
In a preliminary experiment dimethyl itaconate was hydrogenated (0.2 mol% 1–Rh(cod)BF4; 1 atm H2; 25°C; 18 h; CH2Cl2)
to provide 70% of (R)-2-methylsuccinic acid dimethyl ester having an ee of 80%.

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