Serendipitous discovery of a phosphirene-phosphindole rearrangement

Article abstract of DOI:10.1021/om100990r

The reaction of strong Lewis acids with 2-amino-3-phenylphosphirene pentacarbonyltungsten complexes leads to the corresponding 2-aminophosphindoles through the unexpected formation of a bond between phosphorus and one of the ortho carbons of the phenyl ri

Full text of DOI:10.1021/om100990r

348 Organometallics 2011, 30, 348–351
DOI: 10.1021/om100990r
Serendipitous Discovery of a Phosphirene-Phosphindole Rearrangement
Duanghathai Panichakul and Franc-ois Mathey*
Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang
Technological University, 21 Nanyang Link, Singapore 637371
Received October 17, 2010
Summary: The reaction of strong Lewis acids with 2-amino-3-
phenylphosphirene pentacarbonyltungsten complexes leads to
the corresponding 2-aminophosphindoles through the unexpected
formation of a bond between phosphorus and one of the ortho
carbons of the phenyl ring.
tris(pentafluorophenyl)borane ledto a completelyunexpected
ring expansion (eq 2).
The phosphirenylium cation has been characterized for the
first time by Regitz in 19941 as a free species and in 1999 as a
P-W(CO)5 complex.2 In spite of its 2 π aromaticity,3 this
cation appears to be quite difficult to make and must be kept
in liquid SO2 at low temperature. Wanting to stabilize this
type of species for further studies, we noticed that an isoelec-
tronic cyclopropenylidene had been successfully stabilized
using amino substituents.4 Following our work on 2-amino-
phosphirenes,5 we decided to investigate the potential con-
version of 1,2-diaminophosphirenes into 2-aminophosphir-
enylium cations. This research led us to the discovery of a
completely unexpected rearrangement of 2-amino-3-phenyl-
phosphirenes into 2-aminophosphindoles through the for-
mation of a bond between phosphorus and one of the ortho
carbons of the phenyl ring.
The structure of the 2-aminophosphindole (3) was estab-
lished by X-ray crystal structure analysis (Figure 1). In fact, it
is known that commercial tris(pentafluorophenyl)borane
contains water and behaves as a strong protic acid.8 It is
clear that the first step of the reaction is a protonation of the
nitrogen substituent at phosphorus, leading to a replacement
of the P-N by the P-O bond. But the unexpected and
puzzling finding is that another reaction takes place convert-
ing the phosphirene into the phosphindole ring. In order to
avoid the perturbing effect of water, we decided to use
another approach to phosphirenylium ions relying on the
AlCl3-induced dealkylation of 1-β-chloroethylphosphirenes.2,9
The necessary phosphirene 4 was prepared as shown in eq 3.
Results and Discussion
As usual for this kind of strained phosphorus-carbon
heterocycles, we decided to work in the coordination sphere
of tungsten for convenience. The products are easier to syn-
thesize and more stable. The reaction of [PhNHP-W(CO)5]
as generated from the appropriate phosphirane precursor
(1)6 with PhCtC-NiPr27 affords the expected 1,2-diamino-
phosphirene (2) in good yield (eq 1).
The reaction of AlCl3 with 4 at room temperature leads
to the immediate formation of the corresponding phosphin-
dole 6. No phosphirenylium ion is observed, and the β-chlo-
roethyl substituent atphosphorus remains intact. The identifi-
cation of 6 was essentially carried out by NMR spectroscopy.
Particularly significant are the single ethylenic proton at
5.86 ppm (JHP = 22.5 Hz) and the CH2Cl carbon at 39.0 ppm
(JCP = 6.6 Hz) in CDCl3. We also used the already described
aminophosphirenes 7 and 85 to demonstrate the generality of
this ring expansion (eq 4).
Phosphirene 2 shows the expected high-field shift of the 31
P
resonance at ca. -100 ppm. Our initial attempt to convert
2 into the corresponding phosphirenylium by abstraction
of the amino substituent at phosphorus using commercial
*Corresponding author. E-mail: fmathey@ntu.edu.sg.
(1) Laali, K. K.; Geissler, B.; Wagner, O.; Hoffmann, J.; Armbrust,
R.; Eifeld, W.; Regitz, M. J. Am. Chem. Soc. 1994, 116, 9407.
€
(2) Simon, J.; Bergstrasser, U.; Regitz, M. Organometallics 1999, 18,
817.
The phosphindole 9 was characterized by X-ray crystal
structure analysis (Figure 2). To the best of our knowledge,
(3) Eisfeld, W.; Regitz, M. J. Org. Chem. 1998, 63, 2814.
(4) Lavallo, V.; Canac, Y.; Donnadieu, B.; Schoeller, W.; Bertrand,
G. Science 2006, 312, 722.
(5) Panichakul, D.; Mathey, F. Organometallics 2009, 28, 5705.
(6) Deschamps, B.; Mathey, F. Synthesis 1995, 941.
(7) Strobach, D. R. J. Org. Chem. 1971, 36, 1438.
(8) Di Saverio, A.; Focante, F.; Camurati, I.; Resconi, L.; Beringhelli,
T.; D’Alfonso, G.; Donghi, D.; Maggioni, D.; Mercandelli, P.; Sironi, A.
Inorg. Chem. 2005, 44, 5030.
(9) Deschamps, B.; Mathey, F. Tetrahedron Lett. 1985, 26, 4595.
r
pubs.acs.org/Organometallics
Published on Web 12/21/2010
2010 American Chemical Society

Note
Organometallics, Vol. 30, No. 2, 2011 349
Figure 3. Computed structure of 11BH3 at the B3LYP/6-31þ
˚
G(d)-lanl2dz(W) level. Significant distances (A) and angles
Figure 1. X-ray crystal structure analysis of phosphindole 3.
˚
(deg): P16-C1 1.911, P16-C2 1.804, C1-C2 1.410, C1-B41
1.755, C2-N7 1.306; C1-P16-C2 44.48, P16-C1-C28 123.61,
P16-C1-B41 111.77.
Significant distances (A) and angles (deg): P1-W1 2.4885(6),
P1-O6 1.5599(16), P1-C6 1.815(2), P1-C13 1.895(2), C13-N1
1.292(3),C13-C12 1.502(3), C12-C111.507(3),C6-C11 1.398(3),
O6-B21 1.540(3); C6-P1-C13 89.53(9), C6-P1-O6113.
19(9), C13-P1-O6 108.26(9), P1-C13-N1 127.68(16), C12-
C13-N1 122.82(19).
create this bond. In order to shed some light on this unpre-
cedented rearrangement, we decided to study by DFT calcu-
lations the interaction between the aminophosphirene com-
plex 11 and BH3, chosen as the simplest representative Lewis
acid. We suspected that BH3 might coordinate to the carbon
bearing the phenyl substituent. The calculations were carried
out at the B3LYP/6-31G(d)-lanl2dz (W) level. They indeed
confirmed that a well-defined adduct (11BH3) is formed (no
negative frequency). Its structure is shown in Figure 3.
˚
The B-C interaction is weak (1.755 vs 1.59 A for the sum
of the covalent radii) but sufficient to induce a sizable weak-
ening of the corresponding P-C phosphirene bond, which
is elongated from ca. 1.768 in the free species (X-ray)5
˚
to 1.911 A in 11C, and the development of a strong positive
charge at phosphorus (Mulliken charge þ0.63). On this basis,
we suggest that the mechanism of the ring expansion involves
the breaking of the P-C(Ph) phosphirene bond induced by
the Lewis acid, followed by the electrophilic attack of P onto
the ortho carbon of the phenyl ring.
What happens when no phenyl substituent is present on
the phosphirene ring? Under strictly identical conditions as
for 2, the diaminophosphirene 12 reacts with the borane to
give the borane-aniline adduct 13 and a mixture of two
isomeric open-chain secondary phosphines (14a,b) (eq 5).
Figure 2. X-ray crystal structure analysis of phosphindole 9.
˚
Significant distances (A) and angles (deg): P1-W12.5307(3), P1-
C6 1.8032(13), P1-C13 1.8503(13), C12-C13 1.3672(17), C11-
C12 1.4459(18), C6-C11 1.4019(18), C13-N1 1.3640(16); C6-
P1-C13 91.34(6), C13-N1-C14 120.36(12), C13-N1-C17
121.90(11), C14-N1-C17 116.35(11).
2-aminophosphindoles were unknown until now, and thus,
this easy transformation already has a synthetic interest.
However, we were also puzzled by the fact that the ortho
carbon of the phenyl substituent at C2 that becomes bonded
to phosphorus is geometrically far away from this hetero-
atom. A drastic distortion of the molecule is thus needed to
The formula of 13 was established by X-ray crystal
structure analysis. The two isomers of 14 (δ31P(14a) 68.8,

350 Organometallics, Vol. 30, No. 2, 2011
Panichakul and Mathey
˚
Figure 4. X-ray crystal structure analysis of secondary phosphine complex 14a. Significant distances (A) and angles (deg): P1-C13
1.867(10), P1-O1 1.63(2), O1-B1 1.520(14), P1-W1 2.484(12), C13-N1 1.471(13), N1-C25 1.327(11), N1-C221.520(12), C13-C14
1.322(14); O1-P1-C13 107.6(8), W1-P1-C13 109.1(4), W1-P1-O1 125.9(9), P1-C13-C14 127.5(9), P1-C13-N1 116.5(8),
C14-C13-N1 116.0(9), C13-N1-C22 121.4(9), C13-N1-C25 118.4(10), C22-N1-C25 120.2(8).
JHP = 346 Hz, JPW = 298 Hz, major; δ31P(14b) 59.9, JHP
=
141.9 (d, J = 11.5 Hz, dC(N)), 136.2 (d, J = 22.4 Hz, ipso PhN),
130.9 (s, ipso ArC), 130.0 (4 ꢀ ArCH), 127.9 (s, ArCH), 127.8
(s, ArCH), 126.4 (s, ArCH), 122.1 (s, ArCH), 120.0 (2ꢀ ArCH),
96.8 (d, J = 9.6 Hz, dC (ArC-P)), 54.3 (CH), 47.7 (CH), 25.5
(CH3), 22.0 (CH3), 21.5 (CH3), 21.2 (CH3). Exact mass: calcd for
C25H25N2O5PW 648.1010; found 648.1016.
Phosphirene Complex 12. The 1-aminophosphirane complex 1
(0.237 g, 0.5 mmol) and N,N-diisopropyloct-1-yn-1-amine (0.222 g,
1.0 mmol) were heated in 5 mL of toluene at 110 °C for 4 h. After
evaporation of the solvent, the residue was chromatographed
at -5 °C with hexane to give phosphirene as a colorless oil, 12
(0.204 g, 62%).
337 Hz, JPW = 302Hz, minor) syn-crystallize, but itis possible
toextract from theX-ray data the structuralparametersof14a
that are presented in Figure 4. The formation of 14 can be
explained as follows: aftercomplexation bythe Lewis acid and
cleavage of the P-C(Hex) ring bond, the strongly positive
phosphorus abstracts a hydride from the amino group. This
observation confirms the results of the computation and
establishes that the first step of the mechanism of the ring
expansion of phosphirenes to phosphindoles is the cleavage of
the P-C(Ph) ring bond. Besides, it cast a serious doubt on the
possibility to use such a route to prepare amino-stabilized
phosphirenylium ions.
31P NMR (162 MHz, CDCl3): δ -101.0 (s, 1Jpw = 308.3 Hz).
1H NMR (400 MHz, CDCl3): δ 7.17 (t, J = 8.2 Hz, 2H, ArH),
6.94 (t, J = 7.4 Hz, 1H, ArH), 6.74 (d, J = 7.7 Hz, 2H, ArH),
4.00 (d, 2JPH = 22.7 Hz, NH), 3.74 (br s, 2H, 2 ꢀ CH), 2.49-
2.42 (m, 2H, CH2), 1.67-1.59 (m, 2H, CH2), 1.42-1.30 (m, 6H,
3 ꢀ CH3), 1.29-1.19 (m, 12H, 4 ꢀ CH3), 0.90 (t, J = 6.8 Hz, 3H,
CH3). 13C NMR (100 MHz, CDCl3): δ 199.0 (d, J = 32.0 Hz,
trans CO), 196.5 (d, J = 9.6 Hz, cis CO), 142.1 (d, J = 11.3 Hz,
dC(N)), 137.7 (d, J = 12.1 Hz, ipso C(PhNH)), 128.7 (s, meta
CH(Ph)), 121.9 (s, ortho CH(Ph), 120.5 (s, para CH(Ph)), 98.4
(d, J = 2.5 Hz, dC), 31.4 (CH2), 29.2 (CH2), 28.3 (d, J = 3.6 Hz,
CH2), 26.8 (d, J = 3.1 Hz, CH2), 22.5 (CH2), 21.8 (4 ꢀ CH3),
14.0 (CH3). Exact mass: calcd for C25H33N2O5PW 656.1636;
found 656.1658.
Complexes 4 and 5. The 7-β-chloroethyl-7-phosphanorbor-
nadiene complex9 (0.320 g, 0.50 mmol) and N-isopropyl-
N-(phenylethynyl)propan-2-amine (0.201 g, 1.0 mmol) were heated
in 5 mL of toluene with a small amount of CuCl at 60 °C for 1 h.
After evaporation of the solvent, the residue was chromatographed
with hexane-ethyl acetate (90:10) to give phosphirene 4 (0.064 g,
21%) and diphosphetene 5 (0.054 g, 21%) as colorless oils.
Phosphirene 4. 31P NMR (122 MHz, CD2Cl2): δ -143.6
(s, 1Jpw=266.0 Hz). 1H NMR (400 MHz, CD2Cl2): δ 7.54 (d, J =
7.9 Hz, 2H, ortho ArH), 7.43 (t, J = 7.5 Hz, 2H, meta ArH), 7.28
(t, J = 6.7 Hz, 1H, para ArH), 4.03 (sep, 2H, 2 ꢀ CH), 3.45-3.36
(m, 2H, CH2Cl), 2.42-2.34 (m, 2H, CH2), 1.44 (d, J = 6.8 Hz,
6H, 2 ꢀ CH3), 1.39 (d, J = 7.1 Hz, 6H, 2 ꢀ CH3). 13C NMR (100
MHz, CDCl3): δ 193.8 (d, J = 29.5 Hz, trans CO), 196.4 (d, J =
8.4 Hz, cis CO), 141.3 (d, J = 17.0 Hz, dC(N)), 130.6 (s, ipso
ArC), 128.8 (s, meta ArCH), 127.9 (d, J = 6.4 Hz, ortho ArCH),
126.4 (s, para ArCH), 114.1 (s, dCP), 52.1 (CH), 52.0 (CH),
42.5 (d, J = 13.2 Hz, CH2), 40.3 (CH2), 22.5 (2 ꢀ CH3), 22.0
Experimental Section
General Procedure. NMR spectra were obtained on a JEOL
ECA400 or JEOL ECA400SL spectrometer. All spectra were
recorded at 298 K unless otherwise specified. Elemental analyses
were performed in the Division of Chemistry and Biological
Chemistry, Nanyang Technological University. HRMS spectra
were obtained in ESI mode on a Finnigan MAT95XP HRMS
system (Thermo Electron Corp.). X-ray crystallographic anal-
yses were performed on a Bruker X8 APEX diffractometer.
All reactions were performed under argon. Silica gel (230-
400 mesh) was used for the chromatographic separations. All
commercially available reagents were used as received from the
suppliers.
Phosphirene Complex 2. The 1-aminophosphirane complex 1
(0.286 g, 0.6 mmol) and (phenylethynyl)(diisopropyl)amine
(0.242 g, 1.2 mmol) were heated in 5 mL of toluene at 100 °C for
2 h. After evaporation of the solvent, the residue was chromato-
graphed with hexane to give phosphirene as a colorless oil,
2 (0.238 g, 61%).
1
31P NMR (162 MHz, CDCl3): δ -97.8 (s, Jpw= 306.8 Hz,
2JPNH = 26.3 Hz). 1H NMR (400 MHz, CDCl3, -50 °C): δ
7.54-7.38 (m, 4H, ArH), 7.34-7.26 (m, 1H, ArH), 7.11 (d, J =
7.4 Hz, 2H, ArH), 6.90 (t, J = 7.4 Hz, 1H, ArH), 6.75 (d, J = 7.8
Hz, 2H, ArH), 4.23 (d, J = 22.9 Hz, 1H, NH), 4.04 (br sep, 1H,
CH), 3.60 (br sep, 1H, CH), 1.35 (d, J = 6.4 Hz, 3H, CH3), 1.32
(d, J = 6.9 Hz, 3H, CH3), 1.11 (d, J = 6.4 Hz, 3H, CH3), 1.04 (d,
J = 6.4 Hz, 3H, CH3). 13C NMR (100 MHz, CDCl3, -50 °C): δ
199.0 (d, J = 33.5 Hz, trans CO), 196.3 (d, J = 8.6 Hz, cis CO),

Note
Organometallics, Vol. 30, No. 2, 2011 351
(2 ꢀ CH3). Exact mass: calcd for C21H23ClNO5PW 619.0512,
Diphosphetene 6. 31P NMR (162 MHz, CD2Cl2): δ 39.1
J = 8.0, 3.9 Hz, 1H, ArH), 5.78 (d, J = 22.4 Hz, 1H, CH),
3.73 (sep, 2H, 2 ꢀ CH), 1.33 (d, J = 6.7 Hz, 12H, 4 ꢀ CH3).
13C NMR (100 MHz, CDCl3): δ 198.2 (d, J = 23.2 Hz, trans
CO), 196.4 (d, J=6.9 Hz, cis CO), 155.9 (d, J=50.0 Hz, P-C-N),
146.2 (d, J = 13.6 Hz, C-CP), 136.8 (d, J = 52.3 Hz, C-P),
133.2 (ArCH), 133.0 (ArCH), 131.3 (d, J = 2.6 Hz, ArCH),
130.6 (ArCH), 130.5 (d, J = 36.4 Hz, ipso ArC), 129.1 (ArCH),
129.0 (ArCH), 127.9 (d, J = 14.5 Hz, ArCH), 122.1 (d, J = 10.9
Hz, ArCH), 119.8 (d, J = 3.8 Hz, ArCH), 102.3 (d, J = 11.1 Hz,
CH-CP), 50.4 (CH), 46.4 (CH), 20.3 (2 ꢀ CH3), 19.8 (2 ꢀ CH3).
Exact mass: calcd for C25H24NO5PW 633.0901, found 633.0904.
Phosphindole 11. Yield: 0.033 g (56%). 31P NMR (162 MHz,
CDCl3): δ 118.9 (s, Jpw = 280.3 Hz). H NMR (400 MHz,
CDCl3): δ 7.38 (t, J = 7.5 Hz, 1H, ArH), 7.22 (t, J = 7.6 Hz, 1H,
ArH), 6.99 (td, J = 7.4, 4.0 Hz, 1H, ArH), 6.93 (dd, J = 7.6,
2.2 Hz, 1H, ArH), 5.69 (d, J = 22.9 Hz, 1H, CH), 4.11 (br s, 2H,
2 ꢀ CH), 3.37 (d, J = 12.1 Hz, 3H, OCH3), 1.39 (d, J = 6.8 Hz,
6H, 2 ꢀ CH3), 1.35 (d, J = 6.8 Hz, 6H, 2 ꢀ CH3). 13C NMR (100
MHz, CDCl3): δ 198.7 (d, J = 27.0 Hz, trans CO), 196.1 (d, J =
7.6 Hz, cis CO), 155.4 (d, J = 53.4 Hz, P-C-N), 144.8 (d, J =
14.3 Hz, C-CP), 137.5 (d, J = 48.7 Hz, C-P), 132.5 (ArCH),
128.4 (d, J = 17.6 Hz, ArCH), 122.7 (d, J = 7.6 Hz, ArCH),
119.8 (d, J = 2.9 Hz, ArCH), 103.3 (d, J = 18.1 Hz, CH-CP),
55.3 (d, J = 13.4 Hz, OCH3), 21.2 (CH3), 20.5 (CH3). Exact
mass: calcd for C20H22NO6PW 587.0694, found C, 587.0696.
Aniline-Borane Adduct 13 and Secondary Phosphine Complexes
14a,b. Phosphirene 12 (0.145 g, 0.22 mmol) was dissolved in 8 mL
of CH2Cl2, B(C6F5)3 (0.169 g, 0.33 mmol) was added into the
reaction flask at 0 °C, and the mixture was stirred for 30 min. After
evaporation of the solvent, the residue was chromatographed on
silica gel with 80:20 hexane-ethyl acetate to give the B-N adduct
13 then with CH2Cl2 to give 14, both as white crystals.
found 619.0523.
P
(d, 1JPW = 229.4 Hz, JPP=24.3 Hz), 2.90 (d, 1JPW = 243.6 Hz,
J
P
PP= 23.7 Hz). 1H NMR (400 MHz, CD2Cl2): δ 7.43 (t, J =
7.5 Hz, 2H, ArH), 7.39-7.35 (m, 1H, ArH), 7.23 (t, J = 8.2 Hz,
2H, ArH), 3.91-3.87 (m, 4H, 2 ꢀ CH, CH2Cl), 3.86-3.82 (m,
2H, CH2Cl), 3.26-3.10 (m, 2H, CH2), 3.09-2.98 (m, 2H, CH2),
1.37 (d, J = 7.1 Hz, 6H, 2 ꢀ CH3), 1.32 (d, J = 6.7 Hz, 6H, 2 ꢀ
CH3). 13C NMR (100 MHz, CD2Cl2): δ 196.9 (d, J = 26.1 Hz,
trans CO), 196.3 (d, J=26.8 Hz, trans CO), 195.7 (d, J = 5.8 Hz,
cis CO), 195.5 (d, J = 6.7 Hz, cis CO), 150.6 (dd, J = 20.8 and
33.0 Hz, P-C-N), 137.2 (d, J = 9.5 Hz, ipso ArC), 137.0 (d, J =
10.2 Hz, ipso ArC), 129.0 (2 ꢀ ArCH), 128.5 (ArCH), 128.4
(ArCH), 128.3 (ArCH), 114.8 (dd, J = 20.0 and 39.0 Hz, dCP),
53.7 (CH), 53.6 (CH), 43.8 (2 ꢀ CH2), 41.0 (2 ꢀ CH2), 23.6
(2 ꢀ CH3), 22.0 (2 ꢀ CH3). Exact mass: calcd for C28H27Cl2-
NO10P2W2 1036.9506, found 1036.9491.
1
1
Phosphindole Complex 3. Phosphirene 2 (9 mg, 0.014 mmol)
was dissolved in 2 mL of CH2Cl2, B(C6F5)3 (11 mg, 0.021 mmol)
was added into the reaction flask at 0 °C, and the mixture was
stirred for 30 min. After evaporation of the solvent, the residue
was purified by flash column chromatography on silica gel with
80:20 hexane-ethyl acetate then CH2Cl2 to give 3 (0.007 g, 46%)
as white crystals.
31P NMR (162 MHz, CDCl3): δ 98.9 (s, Jpw = 311.1 Hz).
1H NMR (400 MHz, CO(CD3)2): δ 7.61-7.58 (t, J=7.6 Hz, 1H,
ArCH), 7.46-7.39 (m, 3H, ArCH), 5.46 (m, 1H, CH(CH3)2),
4.95 (m, 1H, CH(CH3)2), 4.90-4.73 (m, 2H, CH2), 1.84 (m, 9H,
3 ꢀ CH3), 1.14 (d, J = 6.4 Hz, 3H, CH3). 13C NMR (100 MHz,
CO(CD3)2): δ 198.6 (d, J = 26.8 Hz, trans CO), 198.0 (br,
CdNþ), 196.0 (d, J = 7.9 Hz, cis CO), 147.7 (br d, JCF
=
235.8 Hz, ortho ArCF), 139.1 (d, JCF = 246.9 Hz, para ArCF),
139.3 (d, J=45.9 Hz, benzo-CP), 136.6 (br d, J=247.3 Hz, meta
ArCF), 132.0 (br s, ipso CArB), 131.5 (s, ArCH), 128.0 (d, J =
10.0 Hz, ArCH), 127.8 (d, J =17.6 Hz, ArCH), 125.6 (d, J = 4.0
Hz, ArCH), 64.6 (d, J =6.9 Hz, NCH), 57.8 (s, NCH), 36.84
(d, J=11.5 Hz, CH2), 20.49, 18.84, 18.65, 18.25 (4s, 4ꢀCH3).
Model Procedure for the Preparation of Phosphindoles 6, 9,
and 10. Phosphirene 7 (0.063 g, 0.10 mmol) was dissolved in
5 mL of CH2Cl2, and AlCl3 (14.7 mg, 0.11 mmol) was then
added and stirred at room temperature for 30 min. After evap-
oration of the solvent, CH2Cl2 was added and the solid was
removed by filtration. The residue was chromatographed on
silica gel with hexane-ethyl acetate (80:20) to give phosphindole
9 as white crystals.
Adduct yield: 0.081 g (61%). 1H NMR (400 MHz, CDCl3): δ
7.30-7.22 (m, 3H, overlapping meta and para ArCH), 7.20 (br s,
2H, NH2), 7.08-7.02 (m, 2H, ortho ArCH). 13C NMR (100
MHz, CDCl3): δ 147.7 (d, J = 238.0 Hz, ortho ArCF), 140.3
(d, J = 250.0 Hz, para ArCF), 137.23 (d, J = 247.0 Hz, meta
ArCF), 134.3 (s, ipso ArC), 129.8 (s, 2ꢀArCH), 129.0 (s, ArCH),
122.4 (s, 2 ꢀ ArCH), 116.1 (br s, BArC). 19F NMR (376 MHz,
CDCl3): δ -133.04 (d, 3JFF = 20.0 Hz, 6F, ortho ArCF), -155.6
(t, 3JFF = 21.4 Hz, 3F, para ArCF), -162.4 (td, 3JFF = 24.4, 7.6
Hz, 6F, meta ArCF). Anal. Calcd for C24H7BF15N: C, 47.64; H,
1.17; N, 2.31. Found: C, 47.65; H, 1.06 ; N, 2.31.
Yield of 14: 0.06 g (25%). 31P NMR (162 MHz, CDCl3): δ 68.8
(s, JPW = 298.0 Hz, JPH = 346.2 Hz, major isomer), 59.9
(s, JPW = 302.4 Hz, JPH = 337.4 Hz, minor isomer). Selected
13C NMR data (400 MHz, CDCl3, major isomer): δ 195.84
(d, J = 8 Hz, cis CO), 192.0 (s, CdNþ), 147.8 (d, J = 28 Hz,
dCH). 19F NMR (376 MHz, CDCl3): δ -132.33 (d, 3JFF = 23.1
Hz, 6F, minor isomer of ortho ArCF), -132.6 (d, 3JFF = 24.7
Phosphindole 6. Yield: 25 mg (40%). 31P NMR (162 MHz,
CDCl3): δ 5.2 (s, 1JPW = 228.2 Hz, 2JPH = 22.5 Hz). 1H NMR
(400 MHz, CD2Cl2): δ 7.38 (t, J = 7.6 Hz, 1H, ArH), 7.27
(tt, J = 7.6, 1.2 Hz, 1H, ArH), 7.09 (d, J = 7.6 Hz, 1H, ArH),
7.05 (m, J = 7.4, 3.5, 1.0 Hz, 1H, ArH), 5.86 (d, J = 22.5 Hz, 1H,
CH), 3.94 (sep, 2H, 2 ꢀ CH), 3.40-3.32 (m, 1H, CHHCl),
3.09-3.01 (m, 1H, CHH), 2.73-2.70 (m, 2H, CH2), 1.40 (d, J =
3
Hz, 6F, major isomer of ortho ArCF), -158.6 (t, JFF = 22.3
Hz, 3F, minor isomer of para ArCF), -158.9 (t, 3JFF = 21.6 Hz,
3F, major isomer of para ArCF), -164.4 (m, 6F, meta ArCF).
6.7 Hz, 6H, 2 ꢀ CH3), 1.38 (d, J = 6.8 Hz, 6H, 2 ꢀ CH3). 13
C
NMR (100 MHz, CDCl3): δ 198.2 (d, J = 20.8 Hz, trans CO),
196.1 (d, J=6.8 Hz, cis CO), 153.7 (d, J = 49.7 Hz, P-C-N),
146.4 (d, J = 9.6 Hz, C-CP), 135.0 (d, J = 50.6 Hz, C-P), 131.0
(ArCH), 127.4 (d, J = 15.2 Hz, ArCH), 122.1 (d, J = 10.2 Hz,
ArCH), 120.0 (d, J = 5.1 Hz, ArCH), 104.8 (d, J = 14.2 Hz,
CH-CP), 52.6 (CH), 52.5 (CH), 39.0 (d, J = 6.6 Hz, CH2), 35.6
(d, J=14.7 Hz, CH2), 20.6 (2 ꢀ CH3), 20.0 (2 ꢀ CH3). Exact
mass: calcd for C21H23ClNO5PW 619.0512, found 619.0518.
Phosphindole 9. Yield: 0.039 g (62%). 31P NMR (162 MHz,
Acknowledgment. The authors thank the Nanyang
Technological University and Singapore Ministry of
Education Research Fund Tier 2 (MoE2009-T2-2-065)
for the financial support of this work, Dr. Li Yong Xin
(NTU) for the X-ray crystal structure analyses, and
Mr. Raymond Ong Wei Xiang (NTU) for experimental
help.
1
CDCl3): δ 14.7 (s, JPW = 229.3 Hz). 1H NMR (400 MHz,
Supporting Information Available: X-ray crystal structure
analysis of compounds 3, 9, and 14a. This material is available
free of charge via the Internet at http://pubs.acs.org.
CDCl3): δ 7.62-7.57 (m, 2H, ArH), 7.45-7.37 (m, 3H, ArH),
7.22 (t, J = 7.5 Hz, 1H, ArH), 7.16-7.10 (m, 2H, ArH), 6.90 (td,