An unusual addition and ring-closure reaction of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-benzo-diazaphosphorin-4(1H)-one 2-oxide with carbon disulfide for a new and convenient synthesis of the fused phosphorus heterocyclic compound

Article abstract of DOI:10.1081/SCC-120005432

The reaction of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2- benzodiazaphosphorin-4(1H)-one 2-oxide with carbon disulfide takes an alternative pathway in the use of different bases. The sodium hydride mediated reaction leads to the formation of the tricyclic fused 1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-4-thia-3,4b,4a -thiazphosphaphenanthridine 4a-oxide via addition of H-P bond across the double bond of carbon disulfide followed by intramolecular cyclization. In the presence of triethylamine, refluxing a mixture of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-benzodiazaphosphorin-4(1H)-one 2-oxide with carbon disulfide in benzene takes an unusual course with formation in excellent yield of the first example of fused phosphorus heterocyclic 4-[1′-(β-bromoethyl)-4′-oxo-3′-propyl-1′, 2′,3′,4′-tetrahydro-1,3,2-benzodiazaphosphorin-2′ -sulfide]-1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-3,4b, 4a- thiazphosphaphenanthridine 4a,2′-dioxide, which was confirmed by spectroscopic methods, microanalyses and single crystal X-ray structure determination.

Full text of DOI:10.1081/SCC-120005432

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Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic
Chemistry
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AN UNUSUAL ADDITION AND RING-CLOSURE REACTION
OF 1-(2-BROMOETHYL)-2,3-DIHYDRO- 3-PROPYL-1,3,2-
BENZO-DIAZAPHOSPHORIN-4(1H)-ONE 2-OXIDE WITH
CARBON DISULFIDE FOR A NEW AND CONVENIENT
SYNTHESIS OF THE FUSED PHOSPHORUS HETEROCYCLIC
COMPOUND
a
b
a
Jun-Min Huang , Hui Chen & Ru-Yu Chen
a
Institute of Elemento-Organic Chemistry , National Laboratory of Elemento-Organic
Chemistry , Nankai University , Tianjin, 300071, P.R. China
b
Procter and Gamble Technology (Beijing) Co., Ltd. , Beijing, P.R. China
Published online: 18 Oct 2011.
To cite this article: Jun-Min Huang , Hui Chen & Ru-Yu Chen (2002) AN UNUSUAL ADDITION AND RING-CLOSURE REACTION OF
-(2-BROMOETHYL)-2,3-DIHYDRO- 3-PROPYL-1,3,2-BENZO-DIAZAPHOSPHORIN-4(1H)-ONE 2-OXIDE WITH CARBON DISULFIDE
1
FOR A NEW AND CONVENIENT SYNTHESIS OF THE FUSED PHOSPHORUS HETEROCYCLIC COMPOUND, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:14, 2215-2225, DOI: 10.1081/
SCC-120005432
To link to this article: http://dx.doi.org/10.1081/SCC-120005432
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 14, pp. 2215–2225, 2002
AN UNUSUAL ADDITION AND
RING-CLOSURE REACTION OF
-(2-BROMOETHYL)-2,3-DIHYDRO-
1
3-PROPYL-1,3,2-BENZO-
DIAZAPHOSPHORIN-4(1H)-ONE
2
-OXIDE WITH CARBON DISULFIDE FOR
A NEW AND CONVENIENT SYNTHESIS
OF THE FUSED PHOSPHORUS
HETEROCYCLIC COMPOUND
1
,
2
1
Jun-Min Huang, * Hui Chen, and Ru-Yu Chen
1
Institute of Elemento-Organic Chemistry, National
Laboratory of Elemento-Organic Chemistry, Nankai
University, Tianjin 300071, P.R. China
2
Procter and Gamble Technology (Beijing) Co., Ltd.,
Beijing, P.R. China
ABSTRACT
The reaction of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-
benzodiazaphosphorin-4(1H)-one 2-oxide with carbon disul-
fide takes an alternative pathway in the use of different bases.
The sodium hydride mediated reaction leads to the formation
of the tricyclic fused 1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-
propyl-4-thia-3,4b,4a-thiazphosphaphenanthridine 4a-oxide
*
Corresponding author. E-mail: jmhuang@public.tpt.tj.cn
215
2
DOI: 10.1081/SCC-120005432
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

2
216
HUANG, CHEN, AND CHEN
via addition of H-P bond across the double bond of carbon
disulfide followedby intramolecular cyclization. Inthe presence
of triethylamine, refluxing a mixture of 1-(2-bromoethyl)-
2,3-dihydro-3-propyl-1,3,2-benzodiazaphosphorin-4(1H)-one
2-oxide with carbon disulfide in benzene takes an unusual
course with formation in excellent yield of the first example
0
0
of fused phosphorus heterocyclic 4-[1 -(ꢀ-bromoethyl)-4 -oxo-
0
0
0
0
0
0
3
sulfide]-1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-3,4b, 4a-
-propyl-1 ,2 ,3 ,4 -tetrahydro-1,3,2-benzodiazaphosphorin-2 -
0
thiazphosphaphenanthridine 4a,2 -dioxide, which was
confirmed by spectroscopic methods, microanalyses and
single crystal X-ray structure determination.
Organophosphorus compounds are ubiquitous in nature and they have
[
1–4]
broad applications in the fields of agriculture and medicine.
There has
been a considerably growing interest in heterocyclic compounds due to their
pharmaceutical importance and extensive application in organic synthesis,
and the application of heterocycles is suggested to enhance the biological
[
5–7]
activity and/or offer other diverse properties.
Furthermore, a sizeable
number of endogenous compounds that play a key role in regulation of vari-
ous life processes consists of fused heterocycles. As part of ongoing studies in
our laboratory to develop novel antitumor and antiviral agents with high
[
8]
activity and low toxicity, in previous work, we have reported that 11-
ethoxycarbonylmethyl-6-oxo-3,4,6,11-tetrahydro-1-thio-[1,4,3]thiazaphospho-
rino-[3,4-b][1,3,2]benzodiazaphosphorine 12-oxide (2) was designed
incorporating the proximate thiono and phosphoryl groups into the benzo-
annulated phosphdiamide heterocycle and synthesized by the addition and
ring-closure reaction of 3-(2-chloroethyl)-2,3-dihydro-1-ethoxycarbonyl-
methyl-1,3,2-benzodiazaphosphorin-4(1H)-one 2-oxide (1) with carbon
disulfide in the presence of sodium hydride, as shown in Scheme 1, which also
Scheme 1.

FUSED PHOSPHORUS HETEROCYCLIC COMPOUND
2217
afforded 1,1-bisspiro{11-ethoxycarbonylmethyl-6-oxo-3,4,6,11-tetrahydro-
1,4,3]thiazaphosphorino[3,4-b][1,3,2]benzodiazaphosphorine 12-oxide} (3)
[
in a one-pot procedure at the same time, and the mechanism was outlined
in Scheme 2.
Scheme 2.
Scheme 3.
Herein, we wish to report our further investigation on the reaction of
-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-benzodiazaphosphorin-4(1H)-
1
one 2-oxide (4) with carbon disulfide. Preparation of 4 was readily accom-
plished in a four-step sequence outlined in Scheme 3 starting from the cheap
and available material of o-aminobenzoic acid. In order to protect the
amino group and activate the carbonyl group of o-aminobenzoic acid, we
transformed it into the corresponding cyclic anhydride 5 by the action of
triphosgene that is a safe and stable replacement for phosgene. Therefore,
the reaction of the cyclic anhydride 5 with propyl amine was carried out
under very mild conditions in good yields to provide N-propyl anthranil-
amide 6. Then, the phosphorus reagent 4 could be obtained by the reaction
of N-propyl anthranilamide 6 with 1,2-dibromoethane followed by treat-

2
218
HUANG, CHEN, AND CHEN
ment of the intermediate anthranilamide derivative 7 with phosphorus
[
9]
trichloride. We have reported that the reaction of the cyclic anhydride 8
using 2-bromoethylamine (generated from its hydrobromide salt) in place of
propyl amine provided oxazoline 10 by cyclization of the expected
intermediate anthranilamide derivative 9. Therefore, as the analog of the
phosphorus reagent 1 and 4, 3-(2-bromoethyl)-2,3-dihydro-1-propyl-1,3,2-
benzodiazaphosphorin-4(1H)-one 2-oxide (11) could not be obtained as
shown in Scheme 4.
Scheme 4.
As expected, the tricyclic fused compound 12 was only obtained in
7% yield on the treatment of the phosphorus reagent 4 with carbon disul-
6
fide in the presence of sodium hydride at room temperature according to
1
Scheme 5. H NMR, P NMR and elemental analysis data supported the
31
structure of the compound 12, 1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-
4-thia-3,4b,4a-thiazphosphaphenanthridine 4a-oxide. The spiro fused het-
erocyclic compound 13 was not observed in the experiment. We believe
the compound 12 is formed by the mechanism outlined in Scheme 6,
which involved the nucleophilic addition of the phosphorus reagent 4 con-
Scheme 5.

FUSED PHOSPHORUS HETEROCYCLIC COMPOUND
2219
Scheme 6.
taining a P–H bond to the double bond of carbon disulfide followed by the
fast intramolecular cyclization in a one-pot procedure.
However, in the presence of triethylamine, refluxing a mixture of 4
with carbon disulfide in benzene gave the first example of fused phosphorus
heterocyclic compound 14 in 89% yield, as shown in Scheme 7, which takes
an unusual course and provides a novel method for practical synthesis of
0
0
0
0
0
0
0
4
-[1 -(ꢀ-bromoethyl)-4 -oxo-3 -propyl-1 ,2 ,3 ,4 -tetrahydro-1,3,2-benzodiaza-
0
phosphorin-2 -sulfide]-1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-3,4b,4a-
0
10]
thiazphosphaphenanthridine 4a,2 -dioxide. Its structure was determined by
[
X-ray crystallography and is shown in Figure 1.
Compounds 12 and 13
were not obtained as the products in this experiment. None of the proposed
intermediates in this reaction involved the overall addition of two molecules
of 4 to carbon disulfide and loss of the elements HBr were actually observed,
but the pathway as outlined in Scheme 8 would appear plausible. It is
suggested that the addition of one molecule of 4 to carbon disulfide gives
rise to an ionic intermediate 15, then occurs the ring-closure and rearrange-
Scheme 7.

2
220
HUANG, CHEN, AND CHEN
Scheme 8.
Figure 1. X-ray crystal structure of the fused phosphorus heterocyclic
compound 14.

FUSED PHOSPHORUS HETEROCYCLIC COMPOUND
2221
ment followed by addition with a second molecule of 4 and the fast ring-
closure reaction to form 14.
In conclusion, this study has demonstrated that the unusual addition
and ring-closure reaction of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-
benzodiazaphosphorin-4(1H)-one 2-oxide with carbon disulfide in the
presence of triethylamine could be utilized as a template for a new and
convenient synthesis of fused phosphorus heterocyclic compounds bearing
a (O)P–S–C–P(O) bond structure with special consideration given to the
[
7,11]
biological activity,
significance in many of the most important molecules that control molecular
in which the phosphoryl group is of fundamental
[
12]
replication, cell biochemistry and metabolic processes in all living species.
The synthesis of further examples of this ring system and study of their
chemistry is in progress.
EXPERIMENTAL
Melting points were determined with a model YANACO MP-500
1
31
apparatus and are uncorrected. The H and P NMR spectra were
recorded on a BRUKER AC-P200 instrument. Tetramethylsilane (TMS)
1
was used as an internal standard for H NMR, and 85% phosphoric acid
3
1
(
H PO ) was used as an external standard for P NMR spectroscopy. The
3 4
nuclei that are deshielded relative to their respective standards are assigned
a positive chemical shift. Coupling constants, J, are given in Hz. Elemental
analyses were carried out on a Yana MT-3 instrument. Column chroma-
tography was performed using silica gel H (10–40 mm, Haiyang Chemical
Factory of Qingdao).
Preparation of 3,1-Benzoxazine-2,4(1H)-dione (5)
To a stirred solution of o-aminobenzoic acid (24.69 g, 0.18 mol) in
ꢀ
1
80 mL of acetonitrile at 50–55 C were added dropwise pyridine (28.48 g,
.36 mol) and a solution of triphosgene (17.80 g, 0.06 mol) in 100 mL of
0
dichloromethane at the same time. After completion of the addition, the
ꢀ
temperature of the reaction mixture was maintained at 50–55 C for an
additional 2 h. The solvent was removed under reduced pressure and the
residue was added 200 mL of water. The precipitated solid obtained by
filtration was washed with water followed by chilled dichloromethane,
and dried in a vacuum dryer, yielding 27.72 g (94.4%) of 5, m.p.
ꢀ
237–240 C. The intermediate 5 thus obtained is pure enough for further

2
222
HUANG, CHEN, AND CHEN
ꢀ
manipulations but can be recrystallized from ethanol/water, m.p. 242 C dec.
ꢀ
(
Refs. [13,14], m.p. 243 C dec.).
Preparation of N-Propyl 2-Aminobenzic Amide (6)
To a stirred suspension of 5 (16.31 g, 0.10 mol) in 150 mL of dioxane,
ꢀ
propylamine (8.85 g, 0.15 mol) was added dropwise at 40 C over a period of
ꢀ
30 min. Stirring was continued for an additional 1.5 h at 60–70 C, and then
the solvent was removed under reduced pressure to yield 17.20 g (96.5%) of
, which was used without further purification. Analytical sample was
6
recrystallized from ether, m.p. 101–102 C. H NMR (CDCl , ppm; J, Hz):
ꢀ
1
3
3
0
3
6
.96 (t, 3H, NHCH CH CH , J ¼ 7.4); 1.60 (m, 2H, NHCH CH CH );
2
2
3
HH
2
2
3
.33 (m, 2H, NHCH CH CH ); 5.42 (br, 2H, NH ); 6.14 (br, 1H, C(O)NH);
2 2 3 2
.60–7.34 (m, 4H, C H ). Anal. calcd for C H N O: C, 67.39; H, 7.92;
2
6
4
10 14
N, 15.72. Found: C, 67.50; H, 7.82; N, 15.69.
Preparation of N-Propyl 2-(2-Bromoethyl)aminobenzic Amide (7)
A mixture of 6 (8.91 g, 0.05 mol), 0.1 mol of 1,2-dibromoethane,
sodium bicarbonate (8.4 g, 0.1 mol) and 50 mL of acetonitrile was refluxed
for 6 h, till the spot of 6 disappeared on silica gel TLC developed with the
solvent of ethyl acetate/petroleum ether (1 : 1). The liquid was collected by
filtration followed by washing with ethyl acetate, and then the solvent from
the filtrate was removed under reduced pressure and the residue was chro-
matographed on a column of silica gel using a mixture of ethyl acetate/light
ꢀ
petroleum (b.p. 60–90 C) to elute the intermediate 7, 62.8% yield, m.p.
ꢀ
1–53 C. H NMR (CDCl , ppm; J, Hz): 0.95 (t, 3H, NHCH CH CH ,
3 2 2 3
1
5
3
JHH ¼ 7.4); 1.61 (m, 2H, NHCH CH CH ); 3.35 (m, 2H, NHCH CH CH );
2
2
3
2
2
3
3
4
.58–3.92 (m, 4H, NHCH CH Br); 6.24 (br, 1H, C(O)NH); 6.62–7.38 (m,
2 2
H, C H ); 7.65 (br, 1H, NHCH CH Br). Anal. calcd for C H BrN O:
6
4
2
2
12 17
2
C, 50.54; H, 6.01; N, 9.82. Found: C, 50.49; H, 5.86; N, 9.65.
Preparation of 1-(2-Bromoethyl)-2,3-dihydro-3-propyl-1,3,2-
benzodiazaphosphorin-4(1H )-one 2-Oxide (4)
A mixture of 0.05 mol of 7 and 0.051 mol of phosphorus trichloride
in 250 mL of dry benzene was refluxed for 5 h. Ethyl acetate was added to
the reaction mixture and it was washed with cold dilute sodium bicarbo-
nate followed by brine, dried over Na SO . The solvent collected by filtra-
2
4

FUSED PHOSPHORUS HETEROCYCLIC COMPOUND
2223
tion followed by washing with ethyl acetate was removed under reduced
pressure and the resulting oil was purified by flash chromatography [silica
o
gel 60; ethyl acetate/light petroleum (b.p. 60–90 C), 1 : 1] to give 10.56 g
ꢀ
63.8%) of 4. M.p. 82–84 C. H NMR (CDCl , 200 MHz) ꢁ: 0.96 (t, 3H,
3
1
(
3
NCH CH CH , J ¼ 7.4 Hz), 1.77 (m, 2H, NCH CH CH ), 3.55–4.12
2
2
3
HH
2
2
3
(
(
(
m, 6H, PNCH CH CH þ PNCH CH Br), 6.90–8.26 (m, 4H, C H ), 7.86
PH 3
2
2
3
2
2
6
4
1
31
d, 1H, P(O)H, J ¼ 645.9 Hz). P NMR (CDCl , 80.96 MHz) ꢁ: 5.95
s). Anal. calcd for C H BrN O P: C, 43.52; H, 4.87; N, 8.46. Found:
2
1
2
16
2
C, 43.68; H, 5.05; N, 8.66.
Preparation of 1,2,3,4,4a,4b,5,6-Octahydro-6-oxo-5-propyl-4-thia-
,4b,4a-thiazphosphaphenanthridine 4a-Oxide (12)
3
To a solution of the compound 4 (3.0 mmol) in 20 mL of anhydrous
THF, 3.2 mmol of sodium hydride (80% in mineral oil, pentane washed)
ꢀ
was added at À10 C. Stirring the mixture for 0.5 h produced a dense white
precipitate. The mixture was treated with carbon disulfide (3.2 mmol) drop-
wise, stirred 5 h at room temperature, then poured into ice/water (50 mL)
and extracted with ethyl acetate (3 Â 40 mL). The combined organic extracts
were dried (Na SO ) and the solvent was removed under reduced pressure.
2
4
The resulting residue was chromatographed on a column of silica gel using a
ꢀ
mixture of 40% ethyl acetate/petroleum ether (60–90 C) to elute the product
ꢀ
1
in 67% yield. M.p. 207 C (dec.). H NMR (CDCl , 200 MHz) ꢁ: 0.95 (t, 3H,
3
3
NCH CH CH , J ¼ 7.2 Hz), 1.75 (m, 2H, NCH CH CH ), 2.68 (dm,
2
2
3
HH
2
2
3
2
1
1
H, 1/2 Â SCH CH N, J ¼ 15.9 Hz), 3.52–4.50 (m, 5H, SCH CH N þ
2 2 2 2 3 6 4
2
2
HH
2
2
3
1
/2 Â SCH CH N þ NCH CH CH ), 6.85–8.20 (m, 4H, C H ). P NMR
(
H, 4.63; N, 8.58. Found: C, 47.72; H, 4.45; N, 8.65.
CDCl , 80.96 MHz) ꢁ: 8.95 (s). Anal. calcd for C H N O PS : C, 47.84;
3
13 15
2
2
2
0
0
0
0
0
0
0
Preparation of 4-[1 -(b-Bromoethyl)-4 -oxo-3 -propyl-1 ,2 ,3 ,4 -
0
tetrahydro-1,3,2-benzodiazaphosphorin-2 -sulfide]-1,2,3,4,4a,4b,5,6-
octahydro-6-oxo-5-propyl-3,4b,4a-thiazphosphaphenanthridine
0
4
a,2 -Dioxide (14)
A mixture of 3.0 mmol of 4, 3.2 mmol of carbon disulfide and 6.0 mmol
of dry triethylamine in 20 mL of anhydrous benzene was heated at reflux till
the spot of 4 disappeared on silica gel TLC developed with the solvent of
ethyl acetate/petroleum ether (2 : 1), then the produced triethylamine hydro-
bromide was filtered off. The solvent from the filtrate was removed under
reduced pressure and the residue was chromatographed on a column of

2
224
HUANG, CHEN, AND CHEN
ꢀ
silica gel using a mixture of 60% ethyl acetate/petroleum ether (60–90 C) to
elute the product in 89% yield. The single crystals suitable X-ray
analysis were obtained by recrystallization from mixture solvent
ꢀ
ꢀ
of ethyl acetate and 9petroleum ether (90–120 C). M.p. 192 C (dec.).
1
H NMR (CDCl , 200 MHz) ꢁ: 0.96 (m, 6H, 2 Â NCH CH CH ), 1.74 (m, 4H,
3
2
2
3
2
2
1
ÂNCH CH CH ), 2.47 (dm, 1H, 1/2 Â SCH CH N,
J
HH
ꢁ
2
2
3
2
2
2
3
3 Hz), 3.07 (tm, 1H, 1/2 Â SCH CH N, J ꢁ J ꢁ 13 Hz), 3.35–4.66
2
2
HH
HH
(
m, 10H, 2 Â NCH CH CH þ SCH CH N þ NCH CH Br), 4.80 (dd, 1H,
PH PH 6 4
2
2
3
2
2
2
2
2
3
31
CH, J ¼ 17.7 Hz, J ¼ 14.6 Hz), 6.84–8.22 (m, 8H, 2 Â C H ). P NMR
3
(
for C H BrN O P S : C, 45.67; H, 4.75; N, 8.52. Found: C, 45.58;
CDCl , 80.96 MHz) ꢁ: 10.17 (d), 24.45 (d), J ¼ 31.6 Hz. Anal. calcd
25 31 4 4 2 2
3
PP
H, 4.72; N, 8.65.
ACKNOWLEDGMENTS
This project was supported by the Foundation for University Key
Teacher by the Ministry of Education and the National Natural Science
Foundation of P. R. China.
REFERENCES
1. Fu, H.; Tu, G.Z.; Li, Z.L.; Zhao, Y.F. Synthesis 1998, 855.
2. Huang, J.M.; Chen, R.Y. Heteroatom Chem. 2000, 11, 480.
3. Gorin, B.I.; Ferguson, C.G.; Thatcher, G.R. J. Tetrahedron Lett. 1997,
38, 2791.
4. Huang, J.M.; Chen, R.Y. Heteroatom Chem. 2001, 12, 97.
5. Meier, C. Angew. Chem. Int. Ed. Engl. 1996, 35, 70.
6. Zhou, J.; Qiu, Y.G.; Feng, K.S.; Chen, R.Y. Synthesis 1999, 40, and
references cited therein.
7
8
9
. Zhou, J.; Chen, R.Y. J. Chem. Soc., Perkin Trans. 1 1998, 2917.
. Chen, R.Y.; Bao, R. Synthesis 1990, 137.
. Chen, R.Y.; Bao, R. Synthesis 1989, 618.
À1
1
0. Crystallographic data for 14: C H BrN O P S , M ¼ 657.51 g mol
,
2
5
31
4
4 2 2
monoclinic system, space group P2(1)/c, a ¼ 8.632(2), b ¼ 29.008(6),
ꢀ
3
À3
,
˚
˚
c ¼ 11.634(2) A, ꢀ ¼ 90.35 , V ¼ 2913.1(10) A , Z ¼ 4, D ¼ 1.499 g cm
c
F(000) ¼ 1352, crystal dimensions of 0.30 mm  0.40 mm  0.40 mm.
Data were measured at 293 K on Enraf-Nonius CAD4 diffractometer
with graphite crystal monochromated Mo Kꢂ radiation
˚
(ꢃ ¼ 0.71073 A). The structure of the crystal was solved by the direct
methods (SHELXS-86) and anisotropically refined by full-matrix

FUSED PHOSPHORUS HETEROCYCLIC COMPOUND
2225
2
least-squares on F to final R ¼ 0.0510 and R ¼ 0.1423 with
w
2
2
2
2
2
w ¼ 1/[ꢄ (F ) þ (0.1333P) þ 0.0000P] where P ¼ (F þ 2Fc )/3 using
0
0
ꢀ
ꢀ
4
991 independent reflections ð2:24 ꢂ ꢅ ꢂ 24:97 Þ. Corrections for Lp
factors and empirical absorption type based on PSI-scan technique
were applied to the intensity data. Most of the non-hydrogen atoms
were located from an E-map. The others were determined with succes-
sive difference Fourier syntheses. The hydrogen atoms were added
theoretically from a Fourier map and from expected geometry.
All calculations were performed on a PDP 11/44 computer using
SDP-PLUS program system.
1
1
1. Zhou, J.; Chen, R.Y.; Yang, X.F. Heteroatom Chem. 1998, 9, 369.
2. Sum, V.; Baird, C.A.; Kee, T.P.; Thornton-Pett, M. J. Chem. Soc.,
Perkin Trans. 1 1994, 3183.
1
1
3. Coppola, G.M. Synthesis 1980, 505.
4. Venuti, M.C. Synthesis 1982, 266.
Received in Japan June 12, 2001