Synthesis of camphor-based chiral P,N-ligands

Full text of DOI:10.1134/S1070428011060224

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 6, pp. 952–953. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © I.Z. Ilaldinov, D.A. Fatkulina, R. Kadyrov, 2011, published in Zhurnal Organicheskoi Khimii, 2011, Vol. 47, No. 6, pp. 933–934.
SHORT
COMMUNICATIONS
Synthesis of Camphor-Based Chiral P,N-Ligands
I. Z. Ilaldinova, D. A. Fatkulinaa, and R. Kadyrovb
a Kazan State Technological University, ul. Karla Marksa 68, Kazan, 420015 Tatarstan, Russia
e-mail: ilaldinov@mail.ru
b Evonik Degussa GmbH, Rodenbacher Chaussee 4, Hanau-Wolfdang, 63457 Germany
Received April 15, 2010
DOI: 10.1134/S1070428011060224
We previously proposed [1, 2] to use novel cam-
phor-based chiral compounds for the synthesis of di-
phosphine ligands. While continuing studies in this
line we have synthesized one more chiral structure on
the basis of camphor. Pyrazoles IVa and IVb were
obtained in two steps by analogy with the procedures
reported in [3, 4] (Scheme 1).
IVb, followed by treatment with chloro(diphenyl)-
phosphine on cooling with dry ice gave compounds Va
and Vb (Scheme 2).
Scheme 2.
R
R
Me
Me
Me
Me
(1) t-BuLi
(2) Ph2PCl
N
N
N
N
Br
PPh2
Scheme 1.
O
OMe
Me
Me
MeO
MeO
NHNH2
Br
Me
Me
R
IVa, IVb
Va, Vb
+
O
R = H (a), Me (b).
Me
The structure of compounds IV and V was con-
Ia, Ib
II
firmed by the 1H and 31P NMR and GC–MS data.
R
Br
H
(1R,7S)-3-(2-Bromo-6-methoxyphenyl)-1,10,10-
trimethyl-3,4-diazatricyclo[5.2.1.02,6]deca-2(6),4-di-
ene (IVa). A solution of 24 g (0.11 mol) of 2-bromo-6-
methoxyphenylhydrazine (II) in 100 ml of methanol
was added to a solution of 20 g (0.11 mol) of (1R)-3-
hydroxymethylenecamphor (Ia) in 50 ml of methanol.
A solid immediately separated from the reaction mix-
ture. The mixture was stirred for 2 h, and the precip-
itate was filtered off and washed with 95% ethanol.
Yield of hydrazone IIIa 32.7 g. The product, 21.69 g
(57.2 mmol), was dispersed in 150 ml of acetic acid,
0.5 ml of 47% hydrobromic acid was added, and the
mixture was heated to 80°C and stirred for 2 h at that
temperature. The resulting light brown solution was
cooled, a 2 N solution of sodium hydroxide was added,
and a solid separated. The product was extracted into
diethyl ether, the organic phase was washed with a sat-
urated aqueous solution of sodium hydrogen carbonate
and a saturated aqueous solution of sodium chloride,
dried over MgSO4, and diluted with heptane, and di-
N
Me
Me
N
O
MeO
Me
IIIa, IIIb
R
Me
Me
N
HBr, AcOH
N
Br
Me
MeO
IVa, IVb
R = H (a), Me (b).
Attempts to involve 2-bromo-4,6-dimethylphenyl-
hydrazine instead of 2-bromo-6-methoxyphenylhydra-
zine in the reaction with camphor derivatives Ia and Ib
were unsuccessful. Metalation of pyrazoles IVa and
952

SYNTHESIS OF CAMPHOR-BASED CHIRAL P,N-LIGANDS
953
ethyl ether was slowly removed. Yield of compound
IVa 31.0 g (78%). 1H NMR spectrum (CDCl3), δ, ppm:
0.75 s (3H, CH3), 0.88 s (3H, CH3), 0.91 s (3H, CH3),
1.19 d.d.d (1H, J = 12.0, 9.0, 3.6 Hz), 1.38 m (1H),
1.75 d.d.d (1H, J = 12.0, 9.5, 3.8 Hz), 2.07 t.d.d (1H,
J = 11.8, 9.4, 3.8 Hz), 2.80 d (1H, J = 3.8 Hz), 3.77 s
(3H, OMe), 7.11 d (1H, J = 1.9 Hz), 7.16 d.d (1H, J =
8.4, 2.0 Hz), 7.26 d (1H, J = 8.2 Hz), 7.32 s (1H).
Mass spectrum, m/z (Irel, %): 362, 360 (95), 347 (60),
345 (60), 319 (100), 317 (100).
rated, and the aqueous phase was extracted with di-
ethyl ether. The extract was combined with the organic
phase and dried over MgSO4, and the solvent was
removed. The residue was 3.2 g of a viscous oily
substance which was dissolved in 2 ml of toluene and
purified by column chromatography using hexane–
ethyl acetate (1:4) as eluent. Yield 1.3 g (56%), [α]D22 =
–0.09. 1H NMR spectrum (CDCl3), δ, ppm: 0.68 s (3H,
CH3), 0.81 s (3H, CH3), 0.85 s (3H, CH3), 1.12 d.d.d
(1H, J = 12.1, 9.0, 3.5 Hz), 1.32 m (1H), 1.66 d.d.d
(1H, J = 12.0, 9.4, 3.7 Hz), 1.99 t.d.d (1H, J = 11.8,
9.4, 3.9 Hz), 2.72 d (1H, J = 3.8 Hz), 3.55 s (3H,
OMe), 6.81 d.d.d (1H, J = 7.9, 6.4, 1.5 Hz), 6.85 d.d
(1H, J = 8.3, 1.5 Hz), 7.29–7.25 m (12H). 31P NMR
spectrum (CDCl3): δP –3.0 ppm.
(1R,7S)-3-(2-Bromo-6-methoxyphenyl)-1,5,10,10-
tetramethyl-3,4-diazatricyclo[5.2.1.02,6]deca-2(6),4-
diene (IVb). (1R)-3-Acetylcamphor (Ib), 8.2 g
(42 mmol), was added to a solution of 9.13 g (42 mmol)
of 2-bromo-6-methoxyphenylhydrazine in 70 ml of
methanol. The mixture was stirred for 30 min at room
temperature, 3 drops of 47% hydrobromic acid was
added, the mixture was heated for 5 h under reflux, the
solvent was removed under reduced pressure, and the
residue was applied to silica gel. The product was
isolated by elution with hexane–ethyl acetate (1:1).
The eluate was evaporated, and the residue was recrys-
tallized from 100 ml of hexane. Yield 7.95 g (50%).
1H NMR spectrum (CDCl3), δ, ppm: 0.77 s (3H, CH3),
0.87 s (3H, CH3), 0.89 s (3H, CH3), 1.17 d.d.d (1H, J =
12.0, 8.9, 3.4 Hz), 1.38 m (1H), 1.72 d.d.d (1H, J =
12.0, 9.3, 3.8 Hz), 2.05 t.d.d (1H, J = 11.7, 9.4,
3.8 Hz), 2.24 s (3H, CH3), 2.74 d (1H, J = 3.8 Hz),
3.76 s (3H, OMe), 7.08 d (1H, J = 2.0 Hz), 7.14 d.d
(1H, J = 8.4, 2.0 Hz), 7.26 d (1H, J = 8.2 Hz). Mass
spectrum, m/z (Irel, %): 376 (18), 374 (18), 361 (24),
359 (24), 333 (100), 331 (100).
(1R,7S)-3-(2-Diphenylphosphino-6-methoxy-
phenyl)-1,5,10,10-tetramethyl-3,4-diazatricyclo-
[5.2.1.02,6]deca-2(6),4-diene (Vb) was synthesized in
a similar way from 1.88 g (5 mmol) of compound IVb.
Yield 1.5 g (62%), [α]D22 = –0.07. H NMR spectrum
1
(CDCl3), δ, ppm: 0.69 s (3H, CH3), 0.80 s (3H, CH3),
0.83 s (3H, CH3), 1.09 d.d.d (1H, J = 12.1, 9.0,
3.5 Hz), 1.33 m (1H), 1.63 d.d.d (1H, J = 12.0, 9.4,
3.7 Hz), 1.96 t.d.d (1H, J = 12.0, 9.4, 3.9 Hz), 2.18 s
(3H), 2.65 d (1H, J = 3.9 Hz), 3.55 s (3H, OMe),
6.79 d.d.d (1H, J = 7.9, 6.4, 1.6 Hz), 6.84 d.d (1H, J =
8.3, 1.6 Hz), 7.29–7.25 m (11H). 31P NMR spectrum
(CDCl3): δP –3.05 ppm.
1
The H NMR spectra were recorded on a Bruker
MSL-400 spectrometer at 400.13 MHz. The mass
spectra (electron impact) were obtained on a Trace MS
Finnigan MAT instrument. All initial reagents were
purchased from Aldrich and provided by Evonik
Degussa GmbH.
(1R,7S)-3-(2-Diphenylphosphino-6-methoxyphe-
nyl)-1,10,10-trimethyl-3,4-diazatricyclo[5.2.1.02,6]-
deca-2(6),4-diene (Va). A solution of 1.81 g (5 mmol)
of compound IVa in 20 ml of anhydrous tetrahydro-
furan was cooled to –85 to –90°C, 3.4 ml (5.5 mmol)
of a 1.6 M solution of butyllithium in hexane was
added under argon, the mixture was stirred for 10 min,
and a solution of 1.21 g (5.5 mmol) of chloro(diphe-
nyl)phosphine in 3 ml of THF was added maintaining
the temperature below –85°C. The mixture was care-
fully allowed to warm up to 5°C over a period of 12 h,
50 ml of an aqueous solution of ammonium chloride
was added under argon, the organic phase was sepa-
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 6 2011