Studies on phosphoroheterocycle chemistry III: An unusual way to 1,3,2-thiazaphospholidine-4-thione 2-sulfide derivatives

Article abstract of DOI:10.1055/s-2002-35619

An unusual but efficient method for the synthesis of phosphoroheterocycles, 1,3,2-thiazaphospholidine-4-thione 2-sulfide derivatives, by the reaction of Lawesson's reagent with a variety of α-hydroxy nitriles has been developed. The possible mechanism of the reaction is proposed to involve thiation of hydroxy group in a first step, sequential addition of P-SH to the nitrile and rearrangement resulting in the title phosphoroheterocycles. The preliminary bioassays show that these heterocyclic compounds have herbicidal properties.

Full text of DOI:10.1055/s-2002-35619

PAPER
2527
Studies on Phosphoroheterocycle Chemistry III: An Unusual Way to
1,3,2-Thiazaphospholidine-4-thione 2-Sulfide Derivatives
Synthesis of
1h
e
hospholidin
n
e-4-thione
2
g
-Sulfides Lou Deng,*a RuYu Chenb
a
School of Chemical Engineering, Tianjin University, Tianjin 300072, P. R. China
E-mail: shengloudeng@hotmail.com
b
Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P. R. China
Received 24 June 2002; revised 3 September 2002
mercaptoacetamides with dichlorophosphines10,11 or
tris(diethylamino)phosphine.12 In contrast, our new pro-
cedure seems to be more attractive because of its practical
convenience and efficiency in constructing heterocyclic
Abstract: An unusual but efficient method for the synthesis of
phosphoroheterocycles, 1,3,2-thiazaphospholidine-4-thione 2-sul-
fide derivatives, by the reaction of Lawesson’s reagent with a vari-
ety of -hydroxy nitriles has been developed. The possible
mechanism of the reaction is proposed to involve thiation of hy- systems. Therefore we have developed this new, simple
droxy group in a first step, sequential addition of P–SH to the nitrile
and efficient method for the synthesis of 1,3,2-thiazaphos-
and rearrangement resulting in the title phosphoroheterocycles. The
pholidine-4-thione 2-sulfide derivatives and studied their
preliminary bioassays show that these heterocyclic compounds
biological activity. The synthetic reactions are shown in
have herbicidal properties.
Schemes 1 and 3.
Key words: Lawesson’s reagent -hydroxynitriles, 1,3,2-thiaza-
The starting -hydroxy nitriles 1a–i were routinely pre-
pared by reacting the corresponding aldehydes (or ke-
tones) with sodium cyanide in the presence of dilute
sulfuric acid according to the literature.13 Treatment of -
hydroxy nitriles 1a–f with an equimolar amount of
Lawesson’s reagent in refluxing toluene for 5 hours readi-
ly led to the formation of 1,3,2-thiazaphospholidine-4-
thione 2-sulfides in 58–85% yields (Table 1), together
with the phosphorus heterocycle M. Attempts to optimize
the reaction conditions revealed that the appropriate molar
ratio of Lawesson’s reagent to -hydroxy nitrile should be
1:1. In case of less equivalent amount of Lawesson’s re-
agent, the reaction proceeded with complicated distribu-
tion of the products; while with an excess of it, no
improvement of yields of the expected compounds was
observed. It should be noted that the bulky groups in the
substrates 1a–f decreased the yields of the desired prod-
ucts, presumably due to steric effect. Furthermore, we
also found that higher temperature (>90 °C) accelerated
the reaction and increased the yields of the products, while
lower temperature ( 80 °C) mainly afforded correspond-
ing thiols as well as the heterocycle M. In addition, when
high boiling xylene was used as solvent instead of toluene,
a slight increase of the yields was observed.
phospholidine-4-thione 2-sulfide, herbicidal activity
Studies on the biological activities of phosphorohetero-
cycles have attracted significant attention in past dec-
ades.1–4 Many classes of phosphorus heterocyclic systems
bearing P–O or P–N moieties have proven to be important
biological molecules, such as cyclophosphamide (antitu-
mor alkylating agent),5 cyclic phosphorus-containing
hexapyranose analogues modified at the anomeric carbon
(regulator in carbohydrate linked life process),6 1,4-dihy-
dropyridine-5-cyclic phosphonate derivatives (antihyper-
tensive agent),7and so on. These important results prompt
us to exploit continuously new methodologies for the syn-
thesis of more structurally different phosphoroheterocy-
cles and to study their biological activities.
Recently, we have been attracted by the versatility and
synthetic applicability of Lawesson’s reagent in the con-
struction of functionalized phosphoroheterocycles. We
have very recently described the synthesis of 1,3,2-diaza-
phospholidine-4-thione 2-sulfide derivatives through the
reaction of Lawesson’s reagent with a variety of -amino
nitriles.8 We reasoned that the reaction of Lawesson’s re-
agent with -hydroxy nitriles could proceed in a similar
manner. However, as a result, we exclusively obtained
1,3,2-thiazaphospholidine-4-thione 2-sulfide derivatives,
which previously proved to possess a wide range of bio-
logical activities such as herbicidal,antiviral and fungicid-
al properties.9
The compounds 2a–f were characterized by spectroscopic
methods and microanalyses. Compounds 2e and 2f were
found to be a mixture of diastereoisomers, based on their
1H NMR and 31P NMR spectra. In the 31P NMR spectra
compounds 2e and 2f showed two pairs of peaks ( =
78.88, 75.56, and 77.96, 76.85, respectively). However,
compounds 2b, 2c and 2d showed only one single peak in
their 31P NMR spectra. Futher 31P NMR measurements of
the crude products 2b, 2c and 2d prior to recrystallization
gave the same results, which suggested that only a race-
mate was isolated. Undoutedly, the respective minor dias-
tereoisomer was lost during separation on colum
chromatography. The structure of compound 2a was fur-
A literature search revealed that there are several reports
on the preparation of 1,3,2-thiazaphospholidine-4-
thione(-one) 2-sulfides through cyclocondensation of -
Synthesis 2002, No. 17, Print: 02 12 2002.
Art Id.1437-210X,E;2002,0,17,2527,2531,ftx,en;F05102SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

2528
S. L. Deng, R. Y. Chen
PAPER
gen bonds exist in the form of Sa…HN (a: –x, –y + 1, – z
+ 1). The crystallographic analysis also indicates that
there exists a d–p bond between P and N atoms because
the P–N bond length (1.706 Å) is apparently shorter than
that of a normal single P–N bond (1.76Å).14
Figure 1 ORTEP diagram of compound 2a
Scheme 1
To account for the formation of compounds 2a–f, the gen-
eration of phosphorus heterocycle M may supply impor-
tant information. On the basis of literature, the species M
was often produced via sulfur–oxygen exchange in most
reactions of Lawesson’s reagent with aldehydes,15 ke-
tones,16 amides17 and esters.18 In connection with our re-
action, the formation of compound M at a different
temperature analogously indicates that sulfur–oxygen ex-
change initially takes place, resulting in the corresponding
thiols. On the other hand, some points in the related stud-
ther confirmed by X-ray diffraction analysis. A single
crystal of compound 2a, which was cultured in a mixture
of diethyl ether and light petroleum ether (1:5, v/v), was
subjected to X-ray diffraction analysis. The crystal struc-
ture of 2a is displayed in Figure1. The crystallographic
data and structural refinement for 2a are listed in Table 2.
The crystallographic data reveals that the five-membered
heterocycle is nearly planar and the intermolecular hydro-
Table 1 Compounds 2a–f Prepared
Producta Yield Mp
(%)b (°C)
Molecular
Formulac
31P NMR
(CDCl3)d
1H NMR (CDCl3)
(J, Hz)
2a
2b
2c
2d
85
75
68
62
124–126 C11H14NOPS3 67.87
166–167 C12H16NOPS3 69.05
142–145 C13H18NOPS3 69.72
178–180 C13H18NOPS3 72.47
1.87 (s, 3 H, CH3), 2.01 (s, 3 H, CH3), 3.86 (s, 3 H, OCH3), 7.02 (dd, 2 Harom, 4JPH
= 3.50, 3JH-H = 7.24), 7.96 (dd, 2 Harom, 3JP-H = 10.4, 3JH-H = 7.24), 8.92 (br, 1 H,
NH)
1.11–1.23 (m, 3 H, CH3), 1.88 (s, 3 H, CH3), 1.90–2.43 (dm, 2 H, CH2), 3.87 (s,
4
3
3 H, OCH3), 6.99 (dd, 2 Harom, JP-H = 3.24, JH-H = 7.56), 7.86 (dd, 2 Harom
,
3JP-H = 8.68, 3JH-H = 7.56), 8.74 (br, 1 H, NH)
0.96 (t, 3 H, 3JH-H = 7.26, CH3), 1.48–1.70 (m, 2 H, CH2), 1.96 (s, 3 H, CH3), 1.90–
4
2.30 (m, 2 H, CH2), 3.86 (s, 3 H, OCH3), 6.98 (dd, 2 Harom, JP-H = 3.47,
3JH-H = 7.84), 7.94 (dd, 2 Harom, 3JP-H = 8.97, 3JH-H = 7.84), 8.03 (br, 1 H, NH)
1.10 (d, 3 H, 3JH-H = 7.06, CH3), 1.16 (d, 3 H, 3JH-H = 7.08, CH3), 1.96 (s, 3 H,
CH3), 3.37 (m, 1 H, CH), 3.87 (s, 3 H, OCH3), 6.92 (dd, 2 Harom, 4JP-H = 3.20,
3JH-H = 7.04), 7.98 (dd, 2 Harom, 3JP-H = 9.47, 3JH-H = 7.04), 9.30 (br, 1 H, NH)
2e
2f
59
58
156–158 C12H16NOPS3 78.88, 75.56 1.08–1.21 (m, 6 H, 2 CH3), 3.45 (m, 1 H, CH), 3.88 (s, 3 H, OCH3), 4.71–4.82 (m,
1 H, CH), 6.92–7.08 (m, 2 Harom), 7.93–8.07 (m, 2 Harom), 9.25 (br, 1 H, NH)
65–67
C13H18NOPS3 77.96, 76.85 0.89 (t, 3 H, 3JH-H = 6.89, CH3), 1.21–1.57 (m, 4 H, CH2CH2), 1.87–2.31 (m, 2 H,
CH2), 3.81 (s, 3 H, OCH3), 4.44–4.68 (m, 1 H, CH), 6.94–7.02 (m, 2 Harom), 7.80–
7.92 (m, 2 Harom), 9.20 (br, 1 H, NH)
a FT IR (KBr, cm–1) of compound 2a: 3307(νN–H),1589,1495, 1457 (νAr), 1438, 1260 (νC=S), 1102 (νAr–O–C); 2d: 3425 (νN–H), 1597, 1572, 1502,
1460 (νAr), 1440, 1257 (νC=S), 1128 (νAr–O–C); 2e: 3097 (νN–H), 1590, 1567, 1497, 1466 (νAr), 1414, 1258 (νC=S), 1102 (νAr–O–C); 2f: 3377
(νN–H), 1595, 1570, 1500, 1458 (νAr), 1406, 1255 (νC=S), 1107 (νAr–O–C). EI-MS data of compound 2b: m/z (%) = 317 (M+, 80) 284 (90) 203 (100)
171 (68) 139 (71) 108 (66) 82 (46) 63 (63). 2c: 331 (M+, 75) 298 (78) 289 (39) 203 (100) 171 (70) 139 (25) 128 (86) 108 (82) 63 (77).
b Yield of pure isolated product.
c Satisfactory microanalyses obtained: C±0.4; H±0.4; N±0.4
d The diastereoisomer excess of 2e and 2f based on their 31P NMR spectra are 17% and 22%, respectively.
Synthesis 2002, No. 17, 2527–2531 ISSN 0039-7881 © Thieme Stuttgart · New York

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Synthesis of 1,3,2-Thiazaphospholidine-4-thione 2-Sulfides
2529
study also revealed that the Lawesson’s reagent readily
make a transformation of -amino nitriles into corre-
sponding 1,3,2-diazaphospholidine-4-thione 2-sulfides.8
All of these studies suggested that a nucleophilic addition
of P–SH to the nitrile and rearrangement act as a key step
in the reaction process. Based on these viewpoints, we
propose a possible mechanism for the formation of com-
pounds 2a–f, as depicted in Scheme 2. Thus, thiation of
hydroxy group takes place in the first step; a sequential
nucleophilic attack of mercapto on Lawesson’s reagent
affords thiophosphoric intermediate; further addition of
P–SH to the nitrile and rearrangement give the final prod-
uct 2.
Table 2 Crystal Data and Structure Refinements for 2a
Empirical formula
Color
C11H14NOPS3
Colorless
0.10 0.15 0.25
Triclinic
Crystal size (mm)
Crystal system
Space group
P
Unit-cell dimensions
a = 6.8418 (9) Å
b = 10.5467 (1) Å
c = 11.5670 (2) Å
V
740.72 (16) Å3
Z
2
Formula weight
Density (calc.) (g cm–3)
Absorption coefficient/mm–1
F (000)
303.38
1.360
0.592
316
Data collection
Diffractometer used/scan
Radiation/wavelength
SMART CCD 1000
Mok (graphite monochrom.)/
0.71073 Å
Scheme 2
Temperature/K
range/o
298 (2)
This methodology was also applied to the preparation of
novel spiroheterocyclic compounds, 2-(p-methoxyphe-
nyl)-2,4-dithia-1,3,2-thiazaphospholidine-5,1 -spirocy-
clopentane (3a) and its analogues 3b,c, starting from
cyclic hydroxy nitriles 1g–i as shown in Scheme 3. Under
the conditions described in Scheme 1, besides the hetero-
cycle M, compounds 3a, 3b and 3c were readily obtained
in moderate yields (55, 48 and 42%, respectively). More-
over, it was found that the reaction always ended up with
a certain amount of white precipitate (unidentified poly-
mer). Efforts to increase the yields were made by substi-
tuting xylene as a solvent in place of toluene, yet the
yields of targeted compounds were not improved.
2.14–25.03°
Scan type
Index ranges
–8
h
7, –12
k
7, –9
l
13
Reflections collected
Independent reflections
Absorption correction
Refinement method
Weight
3028
2549 (Rint = 0.0972) ([ I
SADABS
2 (I)])
Full-matrix least-squares on F2
1/[ 2 (F0 ) + (0.0867P) 2]
2
P = (F2 + 2F2c)/3
o
Goodness-of-fit on F2
R, wR [I > 2 (I)]
1.043
0.0476, 0.1272
0.480/–0.258
Largest diff. peak and hole
(e Å–3)
ies previously reported are also helpful for our under-
standing of the reaction mechanism. Petersen et al.
reported earlier that the reaction of Lawesson’s reagent
with 3-oxopropanenitrile derivatives could easily afford a
high yield of 4H-1,3,2-oxazaphosphorin-4-thiones.19 Tes-
ta et al. also found that the treatment of Lawesson’s re-
agent with 3-aminopropenenitrile derivatives led mostly
to the formation of phosphorus-containing uracil ana-
Scheme 3
The preliminary bioassays indicated that the synthesized
phosphoroheterocycles possessed herbicidal activity in a
degree under the concentration of 100 mg/L and 10 mg/L,
which was basically consistent with the study reported in
the literature.9 The testing of herbicidal activity was con-
ducted upon selected plants Brassica campestris and
logue,
1,2-dihydro-2-(4-methoxyphenyl)-1,3,2-diaza-
phosphorin-4-(3H)-thione 2-sulfides.20 Our previous
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S. L. Deng, R. Y. Chen
PAPER
pound M by 1H NMR and 31P NMR spectra was identical to that re-
Echinochloa, and the results are summarized in Table 3.
The evaluation of other biological activities is in progress.
ported earlier in the literature.19
In conclusion, we have developed a new and efficient
method for the synthesis of phosphoroheterocycles 1,3,2-
thiazaphospholidine-4-thione 2-sulfide derivatives by
treatment of Lawesson’s reagent with a variety of -hy-
droxy nitriles. The possible mechanism of the reaction is
proposed to involve thiation of hydroxy group, addition of
P–SH to the nitrile and subsequent rearrangement. The
preliminary bioassay of the prepared phosphoroheterocy-
cles proved to show certain herbicidal activity. We be-
lieve that the present methodology may be useful in the
future design and synthesis of biologically interesting
phosphoroheterocycles.
X-ray Diffraction Analysis of 2a
A colorless crystal of 2a with approximate dimensions of 0.10
mm 0.15 mm 0.25 mm was cultured on a glass fiber in a random
orientation. The determination of the unit cell and the data collec-
tion were performed with MoK radiation ( = 0.71073 Å) on an
Bruker Smart 1000 diffractometer using scan mode. A total of
3028 reflections were collected in the range of 2.14° < < 25.03° at
r.t., in which 2549 reflections with I > 2 (I) were considered to be
observed and used in the successive refinements. The correction for
Lp factors was applied. The structure was determined by direct
method (SHELX-97). Most of the non-hydrogen atoms were locat-
ed from an E-map, the others were determined with successive dif-
ferential Fourier Syntheses. The structure was further refined by
full-matrix least-squares method with anisotropic thermal parame-
ters for all non-hydrogen atoms. The hydrogen atoms were located
theoretically and refined with riding model position parameters and
fixed isotropic thermal parameters. A full-matrix least-squares re-
finement gave final R1 = 0.0476, wR2 = 0.1272 (unit weight) with
All reagents were obtained commercially and used without further
purification, unless otherwise indicated. Toluene and xylene were
dried over sodium before use. Melting points were determined with
a Yanaco MP-500 apparatus and are uncorrected. FTIR spectra
were recorded on a Bio-Bad Exalibur FTS3000 spectrometer. The
1H and 31P NMR spectra were recorded on a Bruker AC-P200 in-
strument. TMS was used as an internal standard for 1H NMR, and
85% phosphoric acid (H3PO4) was used as an external standard for
31P NMR spectroscopy. Elemental analyses were carried out on a
Yanaco MT-3 instrument. EI-MS spectra were recorded with a VG-
7070E spectrometer. Column chromatography was performed us-
ing silica gel H (10–40 m, Haiyang Chemical Factory of Qingdao).
The boiling point of petroleum ether is in the range of 30–60 °C.
2
2
W = 1/[ 2 (Fo ) + (0.0867P)2 ] and P = (Fo + 2Fc2)/3. The maximum
peak in the final difference Fourier maps was 0.480 e/Å3 and the
minimum peak was –0.258 e/Å3. All calculations were performed
on Bruker SMART using SHELXS-97.
2-(p-Methoxyphenyl)-2,4-dithia-1,3,2-thiazaphospholidine-
5,1 -spirocyclopentane (3a) and its Analogues 3b,c; General
Procedure
To a 100 mL 3-necked flask containing anhyd toluene (25 mL) was
added intermediate 1g–i (4 mmol) and Lawesson’s reagent (1.62 g,
4 mmol). Then the mixture was warmed and stirred at reflux for 5
h. The reaction ended up with some precipitation. After removal of
the precipitate by filtration, the solvent was evaporated on a rotary
evaporator under reduced pressure. The resulting residue was chro-
matographed on a silica gel column using a mixture of EtOAc–light
petroleum ether (1:3, v/v) as the eluent to yield the desired com-
pound (Rf 0.7) and another phosphoroheterocycle M (Rf 0.45). The
pure product 3a–c was obtained by recrystallization from a mixture
of CH2Cl2 and petroleum ether (1:5, v/v).
-Hydroxynitriles 1a–i were prepared essentially according to the
literature.13 Lawesson’s reagent was prepared according to the liter-
ature.16
1,3,2-Thiazaphospholidine-4-thione 2-sulfides 2a–f; General
Procedure
A suspension of compound 1a–f (4 mmol) and an equivalent of
Lawesson’s reagent in anhyd toluene (20 mL) were kept stirring at
reflux for 5 h. Then the mixture was cooled to r.t. and subsequently
separated on a silica gel column using a mixture of EtOAc–light pe-
troleum ether (1:3, v/v) as the eluent. The desired fractions
(Rf 0.65–0.7) were collected and evaporated under reduced pres-
sure, affording crude products. The pure products 2a–f were ob-
tained as colorless crystals by recrystallization from a mixture of
Et2O and petroleum ether (1:5, v/v). The fractions (Rf 0.45) gave the
phosphorus heterocycle M as a colorless crystal after evaporation
under reduced pressure (Table 1). The structure elucidation of com-
3a
Colorless crystals; yield: 55%; mp 166–168 °C.
1H NMR (200 MHz, CDCl3): = 1.67–2.96 (m, 8 H, 4 CH2), 3.86
(s, 3 H, OCH3), 6.98 (dd, 2 Harom, 4JP–H = 3.17 Hz, 3JH–H = 8.90 Hz),
7.93 (dd, 2 Harom, 3JP–H = 8.61 Hz, JH–H = 8.90 Hz), 8.26 (br, 1 H,
3
NH).
31P NMR (CDCl3): = 70.24.
Table 3 Herbicidal Activities of Compounds 2a–f and 3a–c
Product
A (%)a
Cc
B (%)b
Cc
Product
A (%)a
Cc
B (%)b
Cc
Dd
Dd
0
Dd
Dd
2a
2b
2c
2d
2e
61.0
48.6
67.9
43.7
29.3
11.2
21.6
23.5
17.3
0
14.3
10.2
34.5
11.7
23.2
2f
44.2
48.4
35.2
14.5
18.5
20.1
12.8
0
28.6
9.4
10.1
0
0
3a
3b
3c
14.6
0
55.5
27.8
24.3
6.5
0
a A: against Brassica campestris.
b B: against Echinochloa.
c C: bio-testing concentration 100 mg/L.
d D: bio-testing concentration 10 mg/L.
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PAPER
Synthesis of 1,3,2-Thiazaphospholidine-4-thione 2-Sulfides
2531
EI-MS: m/z (%) = 329 (M+, 52) 296 (100) 203 (75) 171 (42) 155
(24) 139 (65) 127 (40) 108 (56) 94 (46) 63 (63).
References
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Anal. Calcd for C13H16NOPS3 (329.4): C, 47.42; H, 4.86; N, 4.26.
Found: C, 47.35; H, 4.70; N, 4.28.
3b
Ccolorless crystals; yield: 48%; mp 202–204 °C.
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1H NMR (200 MHz, CDCl3): = 0.91–2.65 (m, 10 H, 5 CH2), 3.86
(s, 3 H, OCH3), 6.98 (dd, 2 Harom, 4JP–H = 3.09 Hz, 3JH–H = 8.79 Hz),
7.51 (dd, 2 Harom, 3JP–H = 8.42 Hz, 3JH–H = 8.79 Hz), 8.34 (br, 1 H,
NH).
31P NMR (CDCl3): = 71.93.
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Kimura, K. Chem. Pharm. Bull. 1987, 35, 4144.
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Anal. Calcd for C14H18NOPS3 (343.4): C, 48.98; H, 5.25; N, 4.08.
Found: C, 48.75; H, 5.41; N, 4.32.
3c
Colorless crystals, yield: 42%; mp 196–198 °C.
(10) Wber, M.; Ugi, I. Liebigs Ann. Chem. 1995, 1555.
(11) Richter, W.; Ugi, I. Synthesis 1990, 661.
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T. M. Zh. Obshch. Khim. 1976, 46, 1688.
(13) Blatt, A. H. Org. Synth., Coll. Vol. 2; Wiley: New York,
1955, 7.
1H NMR (200 MHz, CDCl3): = 1.64–2.82 (m, 12 H, 6 CH2), 3.86
(s, 3 H, OCH3), 6.98 (dd, 2 Harom, 4JP–H = 3.14 Hz, 3JH–H = 8.60 Hz),
7.94 (dd, 2 Harom, 3JP–H = 8.57 Hz, 3JH–H = 8.60 Hz), 8.02 (br, 1 H,
NHC=S).
31P NMR (CDCl3): = 70.93.
(14) Riess, J. G. Phosphorus Sulfur Relat. Elem. 1986, 27, 93.
(15) Nugara, P. N.; Huang, N. Z.; Lakshmikantham, M. V.; Cava,
M. P. Heterocycles 1991, 32, 1559.
(16) Pederson, B. S.; Scheibye, S.; Nilsson, N. H.; Lawesson, S.
O. Bull. Soc. Chim. Belg. 1978, 87, 223.
EI-MS: m/z (%) = 357 (M+, 46) 324 (100) 203 (88) 171 (51) 154
(42) 139 (51) 122 (39) 108 (64) 95 (52) 63 (47).
Anal. Calcd for C15H20NOPS3 (357.5): C, 50.42; H, 5.60; N, 3.92.
Found: C, 50.35; H, 5.50; N, 3.75.
(17) Scheibye, S.; Pederson, B. S.; Lawesson, S. O. Bull. Soc.
Chim. Belg. 1978, 87, 229.
(18) Pederson, B. S.; Scheibye, S.; Clausen, K.; Lawesson, S. O.
Bull. Soc. Chim. Belg. 1978, 87, 293.
(19) Pedersen, B. S.; Lawesson, S. O. Tetrahedron 1979, 35,
2433.
Acknowledgments
Thanks are expressed to Professor HongGeng Wang and his assi-
stant XueBing Leng for X-ray diffraction analysis.
(20) Testa, M. G.; Perrini, G.; Chiacchio, U.; Corsaro, A.
Phosphorus, Sulfur Silicon Relat. Elem. 1994, 86, 75.
Synthesis 2002, No. 17, 2527–2531 ISSN 0039-7881 © Thieme Stuttgart · New York