A Novel and Convenient Synthetic Route to a 9-Phosphatriptycene and Systematic Comparisons of 9-Phosphatriptycene Derivatives

Article abstract of DOI:10.1246/cl.2003.1144

A novel synthetic route to a 9-phosphatriptycene was developed by utilizing ortho-lithiation of a triarylphosphine oxide as a key step. Systematic comparisons of the NMR spectra of 9-phosphatriptycene derivatives indicated the large s character of the lone pair orbital or the phosphorus-chalcogen bonds of the 9-phosphatriptycene derivatives.

Full text of DOI:10.1246/cl.2003.1144

1144
Chemistry Letters Vol.32, No.12 (2003)
A Novel and Convenient Synthetic Route to a 9-Phosphatriptycene and Systematic
Comparisons of 9-Phosphatriptycene Derivatives
Junji Kobayashi, Tomohiro Agou, and Takayuki Kawashimaꢀ
Department of Chemistry, Graduate School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
(Received September 11, 2003; CL-030854)
A novel synthetic route to a 9-phosphatriptycene was devel-
oped by utilizing ortho-lithiation of a triarylphosphine oxide as a
key step. Systematic comparisons of the NMR spectra of 9-phos-
phatriptycene derivatives indicated the large s character of the
lone pair orbital or the phosphorus–chalcogen bonds of the 9-
phosphatriptycene derivatives.
O
O
Me
Me
PhO
Me
Me
O
O
O
O
a
P
P
O
O
O
Me
Me
2
3
Me
O
9-Phosphatriptycene was first synthesized in 1974 by Bick-
elhaupt1 and its unique structure and spectroscopic properties
have attracted the wide varieties of interest of organic chemists.
For example, unusually narrow C–P–C angles compared to those
of Ph3P,2 which were revealed by X-ray crystallographic analy-
sis of 2-tert-butyl-9-phosphatriptycene,3 and extremely up-field
shifts, which were observed in 31P NMR spectra of 9-phospha-
triptycene and 9,10-diphosphatriptycene.4
Me
O
Me
O
OH
C
b
P
O
1
Scheme 1. a: 1) t-BuLi (1.1 eq.), THF, ꢂ78 ꢁC, 2 h, 2)
ClCO2Ph (1.1 eq.), ꢂ78 ꢁC to rt for overnight; b: LDA (2 eq.),
THF, ꢂ78 ꢁC, 5 h.
H
H
lographic analysis has definitively confirmed the structure of 1
and ORTEP drawing is shown in Figure 1.6 This is the first ex-
ample of the crystal structure of a 9-phosphatriptycene oxide.
Triptycene framework has almost C3v symmetry. The P–C bond
LDA
P
Cl
P
δ
P –64.8
ꢀ
lengths (1.774(2), 1.786(7), and 1.795(5) A) are almost same as
Among three synthetic routes to 9-phosphatriptycene report-
ed by Bickelhaupt, ring closure of 9-(2-chlorophenyl)-9,10-di-
hydro-9-phosphaanthracene with an excess of lithium diisopro-
pylamide gave the best result. This synthetic route is, however,
not suitable for a multi-substituted 9-phosphatriptycene because
this reaction proceeded via a benzyne as a reaction intermediate.
Here we report a novel synthetic route to 9-phosphatriptycene by
utilizing ortho-lithiation of tris(3-methoxyphenyl)phosphine ox-
ide 2, which is potentially suitable for symmetrically multi-sub-
stituted 9-phosphatriptycene oxides.
those of triphenylphosphine oxide, but the C–P–C bond angles
(98.5(3), 99.30(11), and 99.5(3)ꢁ) of 1 are narrowed compared
to those (105.82(12), 106.34(13), and 106.43(12)ꢁ) of triphenyl-
phosphine oxide7 due to steric restriction of triptycene frame-
work as observed in 9-phosphatriptycene and its analogs (9,10-
O4
H1
O3
O2
As shown in Scheme 1, a phenoxycarbonyl group was intro-
duced at the ortho-position of tris(3-methoxyphenyl)phosphine
oxide 2 by the reaction of 2 with t-BuLi and subsequent addition
of phenyl chloroformate in 60% yield. 9-Phosphatriptycene ox-
ide 1 was synthesized by treatment of 3 with 2 equivalents of
lithium diisopropylamide (LDA) in 51% yield.5 1H NMR of 1
showed the signal due to the hydroxy proton at ꢀ 6.18, indicating
that the hydroxy group is hydrogen bonded to the methoxy group
intramolecularly, because its chemical shift is significantly
down-field shifted compared with that (ꢀ 5.44) of tris(2-
methoxyphenyl)methanol. The reactivity of the hydroxy group
of 1 also supported the intramolecular hydrogen bonding, that
is, H–D exchange of this hydroxy group only with D2O did
not proceed, but the hydroxy proton was readily exchanged by
the addition of DCl.
O5
C1
P1
O1
Single crystals of 9-phosphatriptycene oxide 1 were ob-
tained by recrystallization from CH2Cl2/MeOH. X-ray crystal-
Figure 1. ORTEP drawing of 9-phosphatriptycene oxide 1
(50% probability).
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.12 (2003)
1145
azaphosphatriptycene8 and 9,10-diphosphatriptycenes4). Inter-
rivatives and the corresponding triarylphosphine derivatives
suggested that the lone pair orbital or the phosphorus–chalcogen
bonds of the 9-phosphatriptycene derivatives have large s char-
acter.
This study was supported by Grant-in-Aid for The 21st
Century COE Program for Frontiers in Fundamental Chemistry
(T. K.) and for Scientific Research (J. K.) from the Ministry of
Education, Culture, Sports, Science and Technology of Japan.
We thank Tosoh Finechem Corporation for the generous gifts
of alkyllithiums.
ꢀ
atomic distance of H1ꢃ ꢃ ꢃO3 is 1.78(3) A, and the bond angle
of O2–H1ꢃ ꢃ ꢃO3 is 149.8(3.3)ꢁ, suggesting the existence of intra-
molecular hydrogen bonding of the hydroxy group with oxygen
atom of the methoxy group in the crystal structure of 1.
References and Notes
1
C. Jongsma, J. P. de Kleijn, and F. Bickelhaupt, Tetrahedron, 30,
3465 (1974).
J. J. Daly, J. Chem. Soc., 1964, 3799.
Scheme 2. a: LR (5 eq.), toluene, reflux, 18.5 h; b: n-Bu3P
(5 eq.), toluene-d8, 130 ꢁC, 110.5 h; c: Se (12 eq.), CDCl3,
75 ꢁC, 5h.
2
3
C. van Rooyen-Reiss and C. H. Stam, Acta Crystallogr., B36,
1252 (1980).
The reaction of 1 with Lawesson’s reagent (LR) afforded 9-
phosphatriptycene sulfide 4 quantitatively, and subsequent re-
duction of 4 with tributylphosphine gave 9-phosphatriptycene
5 in 71% yield.9 9-Phosphatriptycene selenide 6 was quantita-
tively obtained by treatment of 5 with elemental selenium. 31P
NMR signals of 1, 4, 5, and 6 are up-field shifted compared to
those of the corresponding tris(3-methoxyphenyl)phosphine 7,
its oxide 2, sulfide 8, and selenide 9, respectively. As revealed
by X-ray crystallographic analysis, the C–P–C bond angles of
9-phosphatriptycene derivatives are close to 90ꢁ compared to
those of the triarylphosphine derivatives. Therefore, the central
phosphorus atoms are hard to take sp3 hybrid state and results
in increase of p character of the P–C bond. Indeed, the 1JPC val-
ues of 9-phosphatriptycene chalcogenides 1, 4, and 6 are smaller
than those of the corresponding triarylphosphine chalcogenides
2, 8 and 9. On the other hand, the molecular orbital of the lone
pair of 9-phosphatriptycenes and phosphorus–chalcogen bonds
of 9-phosphatriptycene chalcogenides have larger s character
than those of triarylphosphine 7 and its chalcogenides 2, 8 and
9, respectively. Such large s character of the lone pair orbital
and the phosphorus–chalcogen bonds set the central phosphorus
nuclei in the magnetically shielded environments, which causes
4
5
K. G. Weinberg and E. B. Whipple, J. Am. Chem. Soc., 93, 1801
(1971).
1: 1H NMR (500 MHz, CDCl3) ꢀ 3.86 (s, 9H), 6.18 (s, 1H), 6.95
(d, J ¼ 8:3 Hz, 3H), 7.20(td, J ¼ 7:7 and 3.4 Hz, 3H), and 7.62
(dd, J ¼ 12:3 and 7.5 Hz, 3H); 13C{1H} NMR (125 MHz, CDCl3)
ꢀ 57.66 (s), 83.69 (d, J ¼ 23:1 Hz), 117.11 (d, J ¼ 1:9 Hz), 120.62
(d, J ¼ 5:0 Hz), 127.69 (d, J ¼ 14:1 Hz), 134.76 (d, J ¼ 93:0 Hz),
137.75 (d, J ¼ 7:3 Hz), and 157.16 (d, J ¼ 13:5 Hz); 31P NMR
(109 MHz, CDCl3) ꢀ 2.0; HRMS (FABþ): m=z calcd for
C22H20O5P 395.1048; found 395.1031 ([M+H]þ).
Crystallographic data of 1: at ꢂ153 ꢁC, orthorhombic, space
6
ꢀ
group Pna21, a ¼ 16:119ð10Þ, b ¼ 8:122ð5Þ, c ¼ 13:408ð8Þ A,
ꢀ 3
V ¼ 1755:5ð18Þ A , Z ¼ 4, R1 (I > 2:00 ꢁ (I)) = 0.0583, wR2
(all data) = 0.1463 GOF = 1.105. Crystallographic data reported
in this paper have been deposited with Cambridge Crystallograph-
ic Data Centre as supplementary publication no. CCDC-221540.
Copies of the data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam.
ac.uk). Instruction for depositing the crystallographic data is
available on the Web at http://www.ccdc.cam.ac.uk/conts/
depositing.html.
7
8
K. A. Al-Farhan, J. Crystallogr. Spectrosc. Res., 22, 687 (1992).
D. Hellwinkel, W. Schenk, and W. Blaicher, Chem. Ber., 111,
1798 (1978).
1
the up-field shift of 31P NMR. Moreover, the JPSe value of 9-
phosphatriptycene selenide 6 is larger than that of tris(3-methox-
yphenyl)phosphine selenide.
9
4: 1H NMR (500 MHz, CDCl3) ꢀ 3.91 (s, 9H), 6.26 (s, 1H), 6.97
(d, J ¼ 8:5 Hz, 3H), 7.21 (td, J ¼ 8:3 and 3.7 Hz, 3H), and 7.69
(dd, J ¼ 14:8 and 7.2 Hz, 3H); 13C{1H} NMR (125 MHz, CDCl3)
ꢀ 57.69 (s), 116.98 (s), 121.27 (d, J ¼ 8:8 Hz), 127.43 (d,
J ¼ 13:1 Hz), 134.68 (d, J ¼ 75:9 Hz), 136.58 (d, J ¼ 4:3 Hz),
and 157.00 (d, J ¼ 12:0 Hz); 31P NMR (109 MHz, CDCl3) ꢀ
10.0; HRMS (FABþ): m=z calcd for C22H20O4P 379.1099; found
379.1979 ([M+H]þ). 5: 1H NMR (500 MHz, CDCl3) ꢀ 3.89 (s,
9H), 6.33 (s, 1H), 6.86 (d, J ¼ 8:2 Hz, 3H), 7.03 (td, J ¼ 7:7
and 2.3 Hz, 3H), and 7.39 (dd, J ¼ 10:9 and 7.1 Hz, 3H); 13C{1H}
NMR (125 MHz, CDCl3) ꢀ 57.88 (s), 88.65 (s), 116.26 (s), 125.73
(d, J ¼ 38:8 Hz), 126.81 (d, J ¼ 14:6 Hz), 128.49 (d,
J ¼ 12:0 Hz), 132.09 (d, J ¼ 9:9 Hz), and 157.43 (s); 31P NMR
(109 MHz, CDCl3) ꢀ ꢂ68:7; LRMS (EI): m=z 378 (Mþ); HRMS
(FABþ): m=z calcd for C22H20O4PS 411.0820; found 411.0808
(Mþ). 6: 1H NMR (500 MHz, CDCl3) ꢀ 3.92 (s, 9H), 6.30(s,
1H), 6.98 (d, J ¼ 8:0 Hz, 3H), 7.21 (tdd, J ¼ 7:8, 4.0, 1.0 Hz,
3H), 7.71 (ddd, J ¼ 15:6, 7.2, 1.0Hz, 3H); 13C{1H} NMR
(125 MHz, CDCl3) ꢀ 57.76 (s), 117.14 (s), 122,50(d,
J ¼ 10:4 Hz), 127.37 (d, J ¼ 16:1 Hz), 133.55 (d, J ¼ 67:8 Hz),
136.31 (d, J ¼ 2:9 Hz), 156.91 (d, J ¼ 11:3 Hz); 31P NMR
(109 MHz, CDCl3) ꢀ 3.9, 77Se{1H} NMR (95 MHz, CDCl3) ꢀ
601.3 (d, J ¼ 827 Hz).; The signals of the bridgehead carbons
of 4 and 6 were not observed.
In summary, we have reported the novel synthetic route to
the symmetrically tri-substituted 9-phosphatriptycene oxide.
The feature of this way is easy access to 9-phosphatriptycene
from the phosphine oxide only by two steps. Systematic compar-
isons of NMR spectral data between the 9-phosphatriptycene de-
Table 1. Spectroscopic comparisons between 9-phosphatripty-
cene and triarylphosphine derivatives.
1
1
ꢀP
1JPC/Hz JPSe/Hz
ꢀP 1JPC/Hz JPSe/Hz
5
1
4
6
ꢂ68:7
12.0—
2.093.0 —
7
2
8
9
ꢂ2:6
30.3
44.6
38.1
10.9
—
—
—
103.1
84.3
76.0732
10.0
3.9
75.9
67.8
—
827
Published on the web (Advance View) November 17, 2003; DOI 10.1246/cl.2003.1144