Organophosphorus compounds. Part 144: A novel approach to 1,3- oxaphospholes from phosphaalkynes and isomunchnones

Article abstract of DOI:10.1016/S0040-4020(99)00773-5

Phosphaalkynes 5 react with the isomunchnones 12 in a regiospecific process to furnish the 1,3-oxaphospholes 14. In contrast to other cycloadditions to isomunchnones, the bicyclic intermediate 13 cannot be detected in these reactions. It is not necessary to use isolated isomunchnones 12 for the synthesis of the 1,3-oxaphospholes. The reaction sequence is also successful by use of the diazocarbonyl compounds 11 and in situ generation of the isomunchnones therefrom.

Full text of DOI:10.1016/S0040-4020(99)00773-5

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 63–70
Organophosphorus Compounds. Part 144:1 A Novel Approach to
¨
1,3-Oxaphospholes from Phosphaalkynes and Isomunchnones
*
¨
Sven G. Ruf, Uwe Bergstraßer and Manfred Regitz
¨
¨
Fachbereich Chemie der Universitat Kaiserslautern, Erwin-Schrodinger-Straße, D-67663 Kaiserslautern, Germany
Dedicated to Professor Manfred Meisel on the occasion of his 60th birthday
Received 11 May 1999; accepted 13 June 1999
Abstract—Phosphaalkynes 5 react with the isomu¨nchnones 12 in a regiospecific process to furnish the 1,3-oxaphospholes 14. In contrast to
other cycloadditions to isomu¨nchnones, the bicyclic intermediate 13 cannot be detected in these reactions. It is not necessary to use isolated
isomu¨nchnones 12 for the synthesis of the 1,3-oxaphospholes. The reaction sequence is also successful by use of the diazocarbonyl
compounds 11 and in situ generation of the isomu¨nchnones therefrom. ᭧ 1999 Elsevier Science Ltd. All rights reserved.
Introduction
subsequent cleavage of isocyanate (!14) in the presence
of 5.
The 1,3-oxaphospholes represent a rather poorly investi-
gated class of compounds at present. Only three different
approaches to the 1,3-oxaphospholes have as yet been
described. The first synthesis of benzo-condensed 1,3-
oxaphospholes was reported by Heinicke and Tzschach2
in 1985 and involved the reaction of the 2-hydroxyphenyl-
phosphane 1 with the imidoyl chlorides 2.
Synthesis of Isomu¨nchnones 12
The 2-diazomalonic ester chlorides 10 play a key role in our
newly developed synthesis of isomu¨nchnones, their synth-
esis was first described by Padwa.8 The reaction of 10 with
the N-phenylcarboxamides 9—in deprotonated form after
treatment with a strong base such as n-BuLi—at Ϫ78ЊC in
THF as solvent leads to the diazocarbonyl compounds 11
which can be isolated in yields of up to 36% by aqueous
work-up of the reaction mixture. However, since most of the
products 11 are oily substances that cannot be purified by
crystallization and decompose readily on chromatographic
work-up, they are used in the next steps without further
purification. (Scheme 2)
¨
In 1993 Dotz described a synthesis for the 1,3-oxaphos-
pholes 6 without a condensed benzene ring in which the
phosphaalkyne 5 was allowed to react with various
chromium-carbene complexes such as 4.3,4 In most cases
the reaction did not furnish the 1,3-oxaphospholes selec-
tively and the yields were accordingly relatively poor (up
to 35%).
Just recently, Mack and Ruf obtained the bicyclic 1,3-
oxaphospholes 8 by catalytic elimination of nitrogen from
the diazo compounds 7 in the presence of the phosphaalkyne
5.5 The mechanism of this reaction can be explained in
terms of a rearrangement of a phosphirene formed as an
intermediate.6 (Scheme 1)
When the diazocarbonyl compounds 11d–h are heated with
a small amount of rhodium acetate—which acts as a
catalyst—in toluene at 100ЊC the isomu¨nchnones 12d–h
can be isolated in yields of up to 49% after a reaction
time of 30 m. Completion of the reaction can be determined
precisely by IR spectroscopic monitoring of the reaction
mixture. The isomu¨nchnones are obtained as light yellow,
crystalline solids simply by evaporating the reaction
mixture. Some of them are obtained in analytically pure
form by repeated washings with n-pentane and ether. With
regard to yields and reaction times, this catalytic synthesis
of isomu¨nchnones is clearly superior to the synthesis of 12f
previously described by Grub, which involved the thermo-
lysis of 11f for several hours.9 From the point of view of the
mechanism, the formation of the isomu¨nchnones 12
proceeds in two steps: after catalytic cleavage of nitrogen
When we consider the well-investigated reactivity of the
phosphaalkyne 5 towards various mesoionic compounds
such as mu¨nchnones and sydnones,7 it is reasonable to
assume that the isomu¨nchnones 12, which have a carbonyl
ylide dipole form in their mesoionic system, will also
undergo a [3ϩ2] cycloaddition reaction (!13) with
Keywords: mesoionic compounds; phosphaalkynes; cycloadditions.
* Tel.: ϩ49-631-205-2431/2476; fax.: ϩ49-631-205-3921; e-mail:
regitz@rhrk.uni-kl.de
0040–4020/00/$ - see front matter ᭧ 1999 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(99)00773-5

64
S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
Scheme 1.
Scheme 2.

S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
65
Scheme 3.
from the diazo group, an intermediate rhodium carbenoid is
formed and is nucleophilically attacked by the carbonyl
oxygen of the benzoyl group with formation of the
mesoionic five-membered ring system.10 The isomu¨nch-
nones 12 are uniquely characterized by the 13C NMR signals
for the three carbon atoms of the mesoionic five-membered
ring which appear in the regions between dˆ150 to 160
(C2, C4) and dˆ116 to 120 (C5). In addition, the constitu-
tions of products 12 were confirmed by mass spectrometry.
the 1,3-oxaphospholes from the also formed phenyl iso-
cyanate is easily achieved by washing the residue
obtained after evaporation of the reaction mixture with
n-pentane, since the phenyl isocyanate forms a dimer
that is poorly soluble in pentane under the prevailing
reaction conditions.11 The constitutions of the 1,3-
oxaphospholes 14 were confirmed by NMR and mass
spectrometry as well as by elemental analyses. Thus,
for example, the respective 31P NMR signals appear
between dˆ106 and 127, the region typical for
monocyclic 1,3-oxaphospholes.4 The structures of the
1,3-oxaphospholes were elucidated by 13C NMR spec-
troscopy: accordingly, the 13C NMR spectrum of com-
pound 14f contains three characteristic signals for the
carbon atoms of the five-membered oxaphosphole ring
at dˆ192:2; 163:3; and 144:3. The first two signals
exhibit couplings of phosphorus of 55.6 and 53.4 Hz,
Synthesis of 1,3-Oxaphospholes 14
Isomu¨nchnones as starting materials
When the thus prepared isomu¨nchnones 12d–h are
heated with the phosphaalkynes 5a,b in a pressure-
Schlenk tube for 14 h at 120ЊC under an argon over-
pressure of 5 bar, the 1,3-oxaphospholes 14d–h,j are
formed regiospecifically and in very good yields. The
bicyclic intermediates 13d–h,j are presumably formed
in the first step of this 1,3-dipolar cycloaddition process
but cannot be detected by NMR spectroscopy. They
apparently decompose immediately in a retro-Diels-
Alder reaction with cleavage of phenyl isocyanate to
furnish the 1,3-oxaphospholes 14d–h,j. Separation of
1
i.e. with a magnitude typical for JC,P couplings; thus
the respective carbon atoms must be directly bound to
the phosphorus atom. On account of the chemical
environment the 13C NMR signal at dˆ192:2 can be
unequivocally assigned to C2. In the proton-coupled
13C NMR spectrum of 14f the doublet signal at
dˆ192:2 reveals a further triplet structure with a
coupling constant of 4.6 Hz resulting from long-range
couplings with the ortho-protons of the aromatic substituent

66
S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
Table 1. Selected bond distances [A] and angles [Њ] of 14b
˚
P(1)-C(1)
P(1)-C(3)
O1-C2
O(1)-C(3)
C(1)-C(2)
1.785(2)
1.718(3)
1.372(3)
1.352(3)
1.371(3)
C(3)-P(1)-C(1)
C(3)-O(1)-C(2)
C(2)-C(1)-P(1)
C(1)-C(2)-O(1)
O(1)-C(C3)-P(1)
88.97(11)
112.0(2)
121.6(2)
114.9(2)
114.4(2)
Scheme 4.
at C2. These results confirm the 1,3-oxaphosphole struc-
tures of products 14. (Scheme 3)
the diazocarbonyl compounds 11 requires appreciably
shorter reaction times.
The regiochemistry of this 1,3-dipolar cycloaddition is
rather surprising. On consideration of the charge
distribution in the isomu¨nchnone system and the polarity
of the P/C triple bond it is clear that this 1,3-dipolar cycload-
dition does not proceed under charge control. However,
when the reactivity of the isomu¨nchnones 12 with the
phosphaalkynes 5 is considered in comparison with the
corresponding reactions of sydnones and mu¨nchnones,7
clear parallels can be seen with regard to the reaction condi-
tions.
The 1,3-oxaphospholes 14a–c,h,i prepared in this way were
isolated by column chromatography using an n-pentane/
ether mixture as eluant. (Scheme 4)
The catalytic elimination of nitrogen from the diazo group
and the resulting formation of the isomu¨nchnone systems
12a–c,h,i proceeds markedly more rapidly than the feasible
competing reaction of 1,3-dipolar cycloaddition of the diazo
group to the phosphaalkyne 5. This result is in complete
harmony with previously performed reactivity studies on
the 1,3-dipolar cycloaddition of diazocarbonyl compounds
to phosphaalkynes.13
In situ generation of the isomu¨nchnones 12
The structures postulated above for the 1,3-oxaphospholes
14 on the basis of their 13C NMR data were irrevocably
confirmed by an X-ray crystallographic analysis of product
14b (see Fig. 1).
In the chemistry of mesoionic compounds many synthetic
methods are based on the in situ generation of the mesoionic
dipole.12 Thus, the question arises as to whether such a
procedure can be applied in the synthesis of the 1,3-
oxaphospholes 14.
In the crystal state the heterocyclic compound 14b is
characterized by a completely planar structure. Thus, the
five-membered ring skeleton together with the aromatic
substituents lies in one plane. Not only this planar structure
but also the measured bond lengths are indicative of a
delocalized p-electron system (see Table 1). The measured
bond length of the phosphaalkene increment between P1 and
When the diazocarbonyl compounds 11a–c,h,i are heated at
120ЊC for 8 h in the presence of the phosphaalkyne 5a and
Rh2(OAc)4 as catalyst the 1,3-oxaphospholes 14a–c,h,i are
the sole products that can be isolated. The products obtained
by the two synthetic routes are identical in all respects, as
was demonstrated for compound 14h. The yields in this
process reach about 49% and thus are comparable with
the total yields of the 1,3-oxaphospholes obtained in the
syntheses involving the isolated isomu¨nchnones 12d–h. It
would seem in both cases that the yield-determining step is
the formation of the isomu¨nchnones 12. It is also worthy of
note that the direct synthesis of the 1,3-oxaphosphole from
˚
C1 of 1.718(3) A is somewhat stretched in comparison to
typical P/C double bond lengths.15 On the other hand, the
P/C single bond length between P1 and C1 of merely
˚
1.785(2) A is markedly shortened. The value given in the
literature for a P/C single bond not incorporated in a
15
˚
delocalized system is 1.86 A.
Figure 1. X-ray plot and numbering of atoms of 14b. (Molecular Graphics from SHELXTL-Plus14 software package; thermal ellipsoids were drawn at the 33%
probability level. Hydrogen atoms were omitted for reasons of clarity.)

S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
67
The double bond length between the carbon atoms C1 and
C2 amounts to 1.371(0) A and is also somewhat stretched.
MgSO4, and the solvent removed. The thus isolated
products were used without further purification.
˚
However, this value is still clearly smaller than the length of
1.40 A reported for C/C single bonds in phosphabenzenes.
16
˚
Methyl
3-(N-benzoyl-N-phenylamino)-2-diazo-3-oxo-
propanoate (11a). Yield: 2.26 g (35%); IR (CHCl3) n
1
The results of our X-ray crystallographic analysis of the
1,3-oxaphosphole 14b are in good agreement with the
values for other 1,3-oxaphosphole systems reported in the
literature.4
1664 (vs, CO), 2131 (vs, CN2) cmϪ1; H NMR (CDCl3):
d 3.67 (s, 3H, –CO2CH3), 7.10–7.95 (m, 10H, aryl-H);
C17H13N3O4 (323.30).
Methyl
2-diazo-3-[N-(4-methoxybenzoyl)-N-phenyl-
amino]-3-oxopropanoate (11b). Yield: 2.50 g (36%); IR
1
(CHCl3) n 1669 (vs, CO), 2131 (vs, CN2) cmϪ1; H NMR
Conclusion
(CDCl3) d 3.77, 3.92 (each s, 3H, –OCH3, –CO2CH3)
6.95–8.0 (m, 9H, aryl-H); C18H15N3O5 (353.33).
The 1,3-dipolar cycloaddition reactions of isomu¨nchnones
12 with phosphaalkynes 5 described here open a new,
simple, and selective access to the monocyclic 1,3-
oxaphospholes 14. It is not necessary to isolate the
isomu¨nchnones 12 since the reaction sequence starting
from the diazocarbonyl compounds 11 incorporates the
in situ generation of compounds 12 and is equally
successful. Since the reactions of 1,3-oxaphospholes
without a condensed ring have not been reported in the
literature, the present method provides the starting point
for further studies on the reactivity of such 1,3-oxaphos-
pholes.
Methyl 2-diazo-3-[N-(4-ethylbenzoyl)-N-phenylamino]-
3-oxopropanoate (11c). Yield: 2.16 g (31%); IR (CHCl3)
n 1672 (vs, CO), 2128 (vs, CN2) cmϪ1; 1H NMR (CDCl3) d
3
1,24 (t, 3H, JH,Hˆ7.2 Hz, –CH2CH3), 2.59 (q, 2H,
3JH,Hˆ7.2 Hz, –CH2CH3), 3.70 (s, 3H, –CO2CH3),
7.00–7.90 (m, 9H, aryl-H); C19H15N3O4 (349.34).
Methyl 2-diazo-3-[N-(1-naphthoyl)-N-phenylamino]-3-
oxopropanoate (11d). Yield: 2.46 g (33%); IR (CHCl3) n
1
1676 (vs, CO), 2136 (vs, CN2) cmϪ1; H NMR (CDCl3) d
3.73 (s, 3H, –CO2CH3), 6.95–8.15 (m, 12H, aryl-H);
C21H15N3O4 (373.36).
Experimental
Methyl 2-diazo-3-[N-(2-naphthoyl)-N-phenylamino]-3-
oxopropanoate (11e). Yield: 2.54 g (34%); IR (CHCl3) n
All reactions were carried out under argon (purity
Ͼ99.998%) atmosphere using Schlenk techniques. The
solvents were dried by standard procedures, distilled,
and stored under argon prior to use. Compounds 9
and 10 were prepared by published methods.8,17 Column
chromatography was performed in water-cooled glass
tubes under argon. Silica gel was heated for 3 h in
vacuo and then deactivated with 4% water (Brockmann
activity II). Melting points were determined on a
Mettler FP61 apparatus (heating rate 2ЊC/min) and are
1
1674 (vs, CO), 2134 (vs, CN2) cmϪ1; H NMR (CDCl3) d
3.71 (s, 3H, –CO2CH3), 7.00–8.36 (m, 12H, aryl-H);
C21H15N3O4 (373.36).
Ethyl
3-(N-benzoyl-N-phenylamino)-2-diazo-3-oxo-
propanoate (11f). Yield: 2.26 g (35%); C18H17N3O4
(337.33); Analytical data are identical to those given in
the literature.9
Ethyl
2-diazo-3-oxo-3-[N-(2,4,6-trimethylbenzoyl)-N-
uncorrected. Microanalyses were performed with
a
Perkin-Elmer Analyzer 2400. 1H NMR and 13C NMR
spectra were recorded with Bruker AC 200 and Bruker
AMX 400 spectrometers and referenced to the solvent
as internal standard. 31P NMR spectra were measured
on a Bruker AC 200 (80.8 MHz) spectrometer with 85%
H3PO4 as external standard. MS and HRMS were
recorded on a Finnigan MAT 90 spectrometer at
70 eV ionization voltage. IR spectra were measured on
a Perkin-Elmer 16 PC FT-IR spectrophotometer.
phenylamino]-propanoate (11g). Yield: 2.26 g (35%); IR
1
(CHCl3) n 1672 (vs, CO), 2130 (vs, CN2) cmϪ1; H NMR
3
(CDCl3) d 1.16 (t, 3H, JH,Hˆ7.2 Hz, –CH2–CH3), 2.15 (s,
3H, p-CH3), 2.26 (s, 6H, o-CH3), 4.20 (q, 2H, 3JH,Hˆ7.2 Hz,
–CH2–CH3), 6.85 (s, 2H, aryl-H, Mes), 7.01–7.65 (m, 5H,
aryl-H); C21H17N3O4 (379.41).
Ethyl
2-diazo-3-[N-(4-methoxybenzoyl)-N-phenyl-
amino]-3-oxopropanoate (11h). Yield: 2.13 g (29%); IR
1
(CHCl3) n 1678 (vs, CO), 2133 (vs, CN2) cmϪ1; H NMR
3
(CDCl3) d 1.21 (t, 3H, JH,Hˆ7.0 Hz, –CH2–CH3), 3.75 (s,
Alkyl 3-(N-aroyl-N-phenylamino)-2-diazo-3-oxopropan-
oates (11a–i)—general procedure. The appropriate
aromatic N-phenylcarboxamides
3
3H, –OCH3), 4.27 (q, 2H, JH,Hˆ7.0 Hz, –CH2–CH3),
6.95–7.91 (m, 9H, aryl-H); C19H17N3O4 (351.36).
9
(20 mmol) were
dissolved in 50 ml of THF, the solutions were cooled to
Ϫ78ЊC), and treated dropwise with 12.5 ml of a 1.6 M
solution of n-BuLi in n-hexane during 1 h. Stirring was
continued for 30 m more at Ϫ78ЊC and then the 2-diazo-
malonyl chloride ester 10 (20 mmol) was added dropwise to
the mixture. The reaction mixture was allowed to warm to
RT over a period of 24 h. Then the solvent was removed in
vacuo and the residue was dissolved in ether. The organic
layer was washed twice with a saturated NH4Cl solution and
then with water. The organic layer was separated, dried over
Ethyl 2-diazo-3-[N-(4-methylbenzoyl)-N-phenylamino]-
3-oxo-propanoate (11i). Yield: 1.89 g (27%); IR (CHCl3)
n 1668 (vs, CO), 2134 (vs, CN2) cmϪ1; 1H NMR (CDCl3) d
3
1.19 (t, 3H, JH,Hˆ6.9 Hz, –CH2–CH3), 2.35 (s, 3H, p-
3
CH3), 4.27 (q, 2H, JH,Hˆ6.9 Hz, –CH2–CH3), 7.0–7.91
(m, 9H, aryl-H); C19H17N3O5 (367.36).
5-Alkoxycarbonyl-2-aryl-3-phenyl-1,3-oxazolium-4-
olates (12d–h)—general procedure. The diazocarbonyl

68
S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
compounds 11d–h were dissolved in 50 ml toluene and
Rh2(OAc)4 (1 mol%) as catalyst was added. The reaction
flask was placed in an oil bath preheated to 100ЊC. The
evolution of nitrogen was usually finished after 0.5 h,
the end of the reaction is easily recognized by monitor-
ing the reaction mixture with IR (disappearance of the
diazo-band). After evaporation of the solvent and wash-
ing the residue three times with pentane and ether
(10 ml) the isomu¨nchnones 12d–i were isolated as
yellow solids.
–OCH3), 59.7 (s, –CH2–CH3), 116.9 (s, C5), 113.2,
114.7, 127.0, 130.2, 130.4, 130.8, 131.6, 154.0 (each s,
aryl-C), 153.4, 159.4 (each s, C2, C4), 163.9 (s, –CO2Et);
MS: (EI, 70 eV) m/z 339 (30.7) [M]ϩ, 294 (3.8) [M–
C2H5O]ϩ, 267 (8.8) [M–C2H4–CO2]ϩ, 210 (100)
[C14H12NO]ϩ, 135 (48.7) [C8H7O]ϩ, 92 (3.5) [C6H4O]ϩ,
77 (21.5) [C6H5]ϩ; Anal. Calcd for C21H21NO4: C, 67.26;
H, 5.02; N, 4.13. Found: C, 66.40; H, 5.10; N, 4.00.
Alkyl 4-tert-alkyl-2-aryl-1,3-oxaphosphole-5-carboxy-
lates (14)—general procedures
5-Methoxycarbonyl-2-(1-naphthyl)-3-phenyl-1,3-oxazo-
lium-4-olate (12d). Yield: 400 mg (43%); mp 178ЊC; IR
Method A. A solution of equimolar amounts of diazo-
carbonyl compound 11 and phosphaalkyne 5 with a
catalytic amount of Rh2(OAc)4 in 10 ml of toluene was
heated for 8 h at 120ЊC in a Schlenk pressure tube under
5 bar Ar-pressure. The reaction progress was monitored
by 31P NMR spectroscopy. After evaporation of volatile
components a brown residue was obtained. Further puri-
fication was achieved by column chromatography on silica
gel with an n-pentane/diethyl ether mixture (10:1) as
eluant.
1
(CHCl3) n 1686 (vs, CO) cmϪ1; H NMR (CDCl3) d 3.92
(s, 3H, –CH3), 7.22–8.03 (m, 12H, aryl-H); 13C NMR
(CDCl3) d 51.3 (s, –CH3), 118.7 (s, C5), 118.9, 124.1,
124.5, 126.2, 127.4, 128.9, 129.0, 129.7, 129.9, 130.0,
130.5, 131.2, 133.5, 134.2 (each s, aryl-C), 152.7, 155.9
(each s, C2, C4), 159.8 (s, –CO2Et); MS: (EI, 70 eV) m/z
345 (11.6) [M]ϩ, 230 (50.5) [C17H12N]ϩ, 155 (100) [2-
Naph-CO]ϩ, 127 (44.6) [C10H7]ϩ, 77 (16.4) [C6H5]ϩ, 51
(3.8) [C4H3]ϩ; C21H15NO4 (345.36).
5-Methoxycarbonyl-2-(2-naphthyl-)-3-phenyl-1,3-oxazo-
Method B. The isolated isomu¨nchnones 12 were heated
together with an equimolar amount of phosphaalkyne 5 in
10 ml of THF as solvent in a Schlenk pressure tube for 14 h
at 120ЊC under 5 bar Ar-pressure. Monitoring of the reac-
tion mixture with 31P NMR spectroscopy indicated the exact
end of the reaction. After evaporation of the solvent under
vacuum (20ЊC/0.001 mbar) the residue was extracted three
times with pentane (15 ml). The extract was separated from
insoluble material by filtration through a D3 glass sinter
covered with Celite. Final removal of the solvent furnished
the 1,3-oxaphospholes 14.
lium-4-olate (12e). Yield: 370 mg (43%), mp 185ЊC; IR
1
(CHCl3) n 1687 (vs, CO) cmϪ1; H NMR (CDCl3) d 3.86
(s, 3H, –CH3), 7.31–7.89 (m, 12H, aryl-H); 13C NMR
(CDCl3) d 51.3 (s, –CH3), 118.3 (s, C5), 120.1, 122.6,
127.1, 127.8, 127.9, 129.0, 129.2, 129.4, 129.9, 130.4,
130.7, 131.2, 132.2, 135.2 (each s, aryl-C), 153.5, 161.2
(each s, C2, C4), 166.5 (s, –CO2Et); MS (EI, 70 eV) m/z
345 (31.6) [M]ϩ, 230 (100) [C17H12N]ϩ, 155 (68.5)
[2-Naph-CO]ϩ, 127 (37.2) [C10H7]ϩ, 77 (30.7) [C6H5]ϩ,
51 (5.9) [C4H3]ϩ; C21H15NO4 (345.36).
5-Ethoxycarbonyl-2,3-diphenyl-1,3-oxazolium-4-olate
(12f). Yield: 410 mg (44%); mp 153ЊC; Analytical data are
identical to those reported in the literature.9
Methyl
4-tert-butyl-2-phenyl-1,3-oxaphosphole-5-
carboxylate (14a). Yield: 140 mg (48%), (Method A); IR
(CHCl3) n 1728 cmϪ1 (vs, CO); 31P NMR (CDCl3) d 114.9
(s); 1H NMR (CDCl3) d 1.76 (d, 9H, JH,Pˆ1.9 Hz,
4
5-Ethoxycarbonyl-2-(2,4,6-trimethylphenyl)-3-phenyl-
–C(CH3)3), 4.18 (s, 3H, –CO2CH3), 7.59–8.11 (m, 5H,
3
1,3-oxazolium-4-olate (12g). Yield: 550 mg (49%); mp
aryl-H, Ph); 13C NMR (CDCl3) d 31.3 [d, JC,Pˆ11.2 Hz,
207ЊC; IR (CHCl3) n 1686 (vs, CO) cmϪ1
;
1H NMR
–C(CH3)3], 33.9 [d, JC,Pˆ15.2 Hz, –C(CH3)3], 52.2 (s,
2
3
3
(CDCl3) d 1.25 (t, 3H, JH,Hˆ7.0 Hz, –CH2–CH3), 1.96
(s, 3H, p-CH3), 2.14 (s, 6H, p-CH3), 4.25 (q, 2H,
3JH,Hˆ7.0 Hz, –CH2–CH3), 6.75 (s, 2H, aryl-H, Mes),
7.10–7.24 (m, 5H, aryl-H, Ph); 13C NMR (CDCl3):
dˆ14.3 (s, –CH2–CH3), 19.2 (s, o-CH3), 20.9 (s, p-CH3),
59.5 (s, –CH2–CH3), 118.5 (s, C5), 119.1, 124.9, 128.6,
129.1, 129.5, 130.2, 137.6, 142.8 (each s, aryl-C), 151.9,
157.3 (each s, C2, C4), 158.9 (s, –CO2Et); MS: (EI,
70 eV) m/z 351 (18.9) [M]ϩ, 305 (2.4) [M–C2H4–H2O]ϩ,
279 (13.6) [M–C2H4–CO2]ϩ, 222 (100) [C16H16N]ϩ, 147
(44.4) [C10H11O]ϩ, 119 (6.3) [C9H11]ϩ, 77 (22.2) [C6H5]ϩ;
Anal. Calcd for C21H21NO4: C, 71.79; H, 5.98; N, 3.99.
Found: C, 71.30; H, 6.30; N, 3.90.
–CO2CH3), 124.6 (d, JC,Pˆ12.9 Hz, o-C, Ph), 128.8 (s,
5
m-C, Ph), 129.7 (d, JC,Pˆ4.0 Hz, p-C, Ph), 133.7 (d,
2JC,Pˆ12.9 Hz, ipso-C, Ph), 143.9 (d, JC,Pˆ5.6 Hz, C5),
2
1
159.4 (s, –CO2CH3), 164.2 (d, JC,Pˆ53.0 Hz, C4), 192.2
1
(d, JC,Pˆ55.4 Hz, C2); MS (EI, 70 eV): m/z 276 (100.0)
[M]ϩ, 245 (5.9) [M–CH3O]ϩ, 229 (97.5) [M–CH3O2]ϩ,
171 (5.0) [C8H12O2P]ϩ, 105 (61.1) [C7H5O]ϩ, 77 (39.3)
[C6H5]ϩ, 51 (7.8) [C4H3]ϩ; HRMS for C15H17O3P Calcd:
276.0915. Found: 276.0914.
Methyl 4-tert-butyl-2-(4-methoxyphenyl)-1,3-oxaphos-
phole-5-carboxylate (14b). Yield: 251 mg (36%), (Method
A); IR (CHCl3): n 1720 cmϪ1 (vs, CO); 31P NMR (CDCl3):
d 108.2 (s); 1H NMR (CDCl3): d 1.51 [d, 9H, 4JH,Pˆ2.0 Hz,
–C(CH3)3], 3.82, 3.92 (each s, 3H, –OCH3, –CO2CH3),
6.88, 7.80 (2d, 4H, aryl-H, Ph); 13C NMR (CDCl3) d 31.1
5-Ethoxycarbonyl-2-(4-methoxyphenyl)-3-phenyl-1,3-
oxazolium-4-olate (12h). Yield: 388 mg (42%), mp 158ЊC;
1
3
2
IR (CHCl3): n 1690 (vs, CO) cmϪ1; H NMR (CDCl3): d
[d, JC,Pˆ11.3 Hz, –C(CH3)3], 33.7 [d, JC,Pˆ14.5 Hz,
3
1.49 (t, 3H, JH,Hˆ7.1 Hz, –CH2–CH3), 3.95 (s, 3H,
–C(CH3)3] 52.0, 55.2 (each s, –OCH3, –CO2CH3), 114.1
3
3
–OCH3), 4.80 (q, 2H, JH,Hˆ7.1 Hz, –CH2–CH3), 6.98,
(s, m-C), 126.2 (d, JC,Pˆ12.1 Hz, o-C), 126.8 (d,
2
7.62 (each d, 2H, aryl-H), 7.49–7.69 (m, 5H, aryl-H, Ph);
2JC,Pˆ12.9 Hz, ipso-C), 143.1 (d, JC,Pˆ5.6 Hz, C5), 159.2
13C NMR (CDCl3): d 14.6 (s, –CH2–CH3), 55.6 (s,
(s, –CO2CH3), 160.8 (d, JC,Pˆ4.0 Hz, p-C), 164.2
5

S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
69
1
1
(d, JC,Pˆ53.0 Hz, C4), 192.2 (d, JC,Pˆ56.2 Hz, C2);
MS (EI, 70 eV): m/z 306 (100.0) [Mϩ], 275 (3.75)
[Mϩ–CH3O], 259 (28.7) [Mϩ–CH3O2], 171 (1.2)
[C8H12O2Pϩ], 135 (30.7) [C8H7O2ϩ], 57 (12.8) [C4H9ϩ];
Anal. Calcd for C16H19O4P: C, 62.75; H, 6.21. Found: C,
62.99; H, 6.04.
(CHCl3) n 1714 cmϪ1 (vs, CO); 31P NMR (CDCl3) d
1 3
113.1 (s); H NMR (CDCl3): d 1.38 (t, 3H, JH,Hˆ7.2 Hz,
–CO2CH2CH3), 1.48 [d, 9H, 4JP,Hˆ2.2 Hz, –C(CH3)3], 4.36
3
(q, 2H, JH,Hˆ7.2 Hz, –CO2CH2CH3), 7.30–7.82 (m, 5H,
aryl-H); 13C NMR (CDCl3) d 14.2 (s, –CO2CH2CH3), 31.3
3
2
[d, JC,Pˆ10,9 Hz, –C(CH3)3], 33.6 [d, JC,Pˆ15.3 Hz,
–C(CH3)3], 61.2 (s, –CO2CH2CH3), 124.5 (d,
3JC,Pˆ12,1 Hz, o-C, Ph), 128.7 (s, m-C, Ph), 129.5 (d,
Methyl 4-tert-butyl-2-(4-ethylphenyl)-1,3-oxaphosphole-
5-carboxylate (14c). Yield: 130 mg (38%), (Method A); IR
(CHCl3) n 1728 cmϪ1 (vs, CO); 31P NMR (CDCl3) d 112.1
5JC,Pˆ3.0 Hz, p-C, Ph), 133.8 (d, JC,Pˆ13.1 Hz, ipso-C,
2
2
3
Ph), 144.3 (d, JC,Pˆ5.5 Hz, C5), 158.9 (d, JC,Pˆ2.2 Hz,
(s); 1H NMR (CDCl3) d 1.16 (t, 3H, JH,Hˆ7.6 Hz,
–CO2CH2CH3), 163.3 (d, JC,Pˆ53.4 Hz, C4), 192.2 (d,
3
1
4
–CH2CH3), 1.48 [d, 9H, JH,Pˆ1.9 Hz, –C(CH3)3], 2.57 (q,
1JC,Pˆ55.6 Hz, C2); MS (EI, 70 eV) m/z 290 (100.0)
[M]ϩ, 275 (2.2) [M–CH3]ϩ, 245 (2.9) [M–C2H5O]ϩ, 229
(69.4) [M–C2H5O2]ϩ,105 (18.8) [Ph-CO]ϩ, 77 (11.9)
[C6H5]ϩ, 51 (2.4) [C4H3]ϩ; Anal. Calcd. for C16H19O3P:
C, 66.21; H, 6.57. Found: C, 65.50; H, 6.60.
3
2H, JH,Hˆ7.6 Hz, –CH2CH3), 3.87 (s, 3H, –CO2CH3),
7.14, 7.62 (each d, 4H, aryl-H, Ph); 13C NMR (CDCl3) d
15.2 (s, –CH2CH3), 28.7 (s, –CH2CH3), 31.1 [d,
3JC,Pˆ10.4 Hz, –C(CH3)3], 33.7 [d, 2JC,Pˆ15.2 Hz,
3
–C(CH3)3], 51.9 (s, –CO2CH3), 124.5 (d, JC,Pˆ12.0 Hz,
2
o-C), 128.8 (s, m-C), 131.2 (d, JC,Pˆ12.0 Hz, ipso-C),
Ethyl
4-tert-butyl-2-(2,4,6-trimethylphenyl)-1,3-oxa-
2
5
143.4 (d, JC,Pˆ4.8 Hz, C5), 146.1 (d, JC,Pˆ3.2 Hz, p-C),
159.4 (s, –CO2CH3), 163.9 (d, 1JC,Pˆ53.0 Hz, C4), 192.3 (d,
1JC;Pˆ56.2 Hz, C2); MS (EI, 70 eV) m/z 304 (100.0) [M]ϩ,
289 (6.6) [M–CH3]ϩ, 273 (4.9) [M–CH3O]ϩ, 257 (49.0)
[M–CH3O2]ϩ, 171 (2.8) [C8H12O2P]ϩ, 133 (53.2)
[C9H9O]ϩ, 105 (7.5) [C6H4C2H5]ϩ, 77 (7.8) [C6H5]ϩ;
HRMS Calcd for C17H21O3P: 304.1228. Found: 304.1235.
phosphole-5-carboxylate (14g). Yield: 89 mg (72%),
(Method B), IR (CHCl3) n 1710 cmϪ1 (vs, CO); 31P
1
NMR (CDCl3) d 128.9 (s); H NMR (CDCl3) d 1.29 (t,
3H, 3JH,Hˆ7.2 Hz, –CO2CH2CH3), 1.47 [d, 9H,
4JH,Pˆ1.7 Hz, –C(CH3)3), 2.20 (s, 6H, o-CH3), 2.24 (s,
3
3H, p-CH3), 4.28 (q, 2H, JH,Hˆ7.2 Hz, –CO2CH2CH3),
6.90 (s, 2H, Mes); 13C NMR (CDCl3) d 14.2 (s,
4
–CO2CH2CH3), 21.1 (s, p-CH3), 21.2 (d, JC,Pˆ3.2 Hz,
3
Methyl 4-tert-butyl-2-(1-naphthyl)-1,3-oxaphosphole-5-
carboxylate (14d). Yield: 201 mg (85%), (Method B);
mp 121ЊC; IR (CHCl3) n 1721 cmϪ1 (vs, CO); 31P NMR
o-CH3), 31.5 [d, JC,Pˆ10.4 Hz, –C(CH3)3], 33.7 [d,
2JC,Pˆ14.5 Hz, –C(CH3)3], 61.2 (s, –CO2CH2CH3), 128.7
(s, m-C, Mes), 130.4 (d, 2JC,Pˆ12.0 Hz, ipso-C, Mes), 137.5
1
3
(CDCl3) d 126.8 (s); H NMR (CDCl3) d 1.65 [d, 9H,
(d, JC,Pˆ4.0 Hz, o-C, Mes), 138.9 (s, p-C, Mes), 144.3 (d,
4JH,Pˆ2.0 Hz, –C(CH3)3], 3.99 (s, 3H, –CO2CH3), 7.43–
8.06 (m, 7H, 1-naphthyl); 13C NMR (CDCl3) d 31.4 [d,
3JC,Pˆ10.4 Hz, –C(CH3)3], 34.0 [d, 2JC,Pˆ15.3 Hz,
–C(CH3)3], 52.3 (s, –CO2CH3), 125.6, 126.7 (each d,
3JC,Pˆ13.7 and 12.0 Hz, C2, C8a, 1-naphthyl), 125.2,
126.1, 127.3, 128.8, 129.7, 134.0, (each s, C 1-naphthyl),
2JC,Pˆ4.8 Hz, C5), 159.3 (s, –CO2CH2CH3), 163.0 (d,
1
1JC,Pˆ55.4 Hz, C4), 192.2 (d, JC,Pˆ54.6 Hz, C2); MS
(EI, 70 eV) m/z 332 (100.0) [M]ϩ, 287 (2.3)
[M–C2H5O]ϩ, 271 (7.3) [M–C2H5O2]ϩ, 147 (15.7)
[Mes-CO]ϩ, 119 (6.1) [C6H2(CH3)3]ϩ; HRMS Calcd. for
C19H25O3P: 332.1541. Found: 332.1542.
5
130.4 (d, JC,Pˆ2.4 Hz, C-4, 1-naphthyl), 130.9 (d,
3JC,Pˆ9.6 Hz, C-1, 1-naphthyl), 144.2 (d, JC,Pˆ5.6 Hz, C-
Ethyl
4-tert-butyl-2-(4-methoxyphenyl)-1,3-oxaphos-
2
3
1
5), 159.5 (d, JC,Pˆ1.6 Hz, –CO2CH3), 163.7 (d, JC,P
ˆ
phole-5-carboxylate (14h). Yield: 77 mg (45%), (Method
1
54.6 Hz, C-4), 192.4 (d, JC,Pˆ57.8 Hz, C-2); MS (EI, 70
eV): m/z 326 (100) [M]ϩ, 295 (3.1) [M–CH3O]ϩ, 155 (39.1)
[Naph-CO]ϩ, 127 (27.6) [C10H7]ϩ; C19H19O3P (326.33).
A). Yield: 98 mg (81%), (Method B); IR (CHCl3)
1
n 1718 cmϪ1 (vs, CO); 31P NMR (CDCl3) d 107.4 (s); H
NMR (CDCl3) d 1.37 (t, 3H, 3JH,Hˆ7.2 Hz, –CO2CH2CH3),
1.45 [d, 9H, 4JH,Pˆ2.0 Hz, –C(CH3)3], 3.77 (s, 3H, –C6H4–
3
Methyl 4-tert-butyl-2-(2-naphthyl)-1,3-oxaphosphole-5-
carboxylate (14e). Yield: 191 mg (89%), (Method B);
mp 122ЊC; IR (CHCl3) n 1720 cmϪ1 (vs, CO); 31P NMR
(CDCl3) d 126.4 (s); 1H NMR (CDCl3) d 1.54 [d, 9H,
4JH,Pˆ2.0 Hz, –C(CH3)3], 3.94 (s, 3H, –CO2CH3), 7.41–
8.32 (m, 7H, 2-naphthyl); 13C NMR (CDCl3) d 31.7 [d,
3JC,Pˆ10.7 Hz, –C(CH3)3], 34.3 (d, 2JC,Pˆ14.5 Hz,
–C(CH3)3], 52.6 (s, –CO2CH3), 123.3, 123.5 (each d,
3JC,Pˆ12.2 and 13.7 Hz, C1, C3, 2-naphthyl), 127.1,
127.2, 127.3, 128.2, 128.9, 129.1, (each s, C 2-naphthyl),
OCH3), 4.34 (q, 2H, JH,Hˆ7.2 Hz, –CO2CH2CH3), 6.84,
7.76 (each d, 4H, aryl-H); 13C NMR (CDCl3) d 14.2 (s,
3
–CO2CH2CH3), 31.3 [d, JC,Pˆ10.2 Hz, –C(CH3)3], 33.7
2
[d, JC,Pˆ15.3 Hz, –C(CH3)3], 55.3 (s, –C6H4–OCH3),
61.1 (s, –CO2CH2CH3), 114.1 (s, m-C, aryl), 126.3 (d,
2
3JC,Pˆ11.9 Hz, o-C, aryl), 127.0 (d, JC,Pˆ12.7 Hz, ipso-
2
C, aryl), 143.6 (d, JC,Pˆ5.1 Hz, C5), 158.9 (d,
5
3JC,Pˆ2.6 Hz, –CO2CH2CH3), 160.9 (d, JC,P ˆ3.4 Hz,
1
p-C, aryl), 163.7 (d, JC,Pˆ53.4 Hz, C4), 192.3 (d,
1JC,Pˆ55.1 Hz, C2); MS (EI, 70 eV) m/z 320 (100.0)
[M]ϩ, 275 (2.9) [M–C2H5O]ϩ, 259 (26.5) [M–C2H5O2]ϩ,
77 (3.9) [C6H5]ϩ; Anal. Calcd. for C16H19O3P: C, 63.75; H,
6.56. Found: C, 63.50; H, 6.50.
2
131.5 (d, JC,Pˆ12,2 Hz, C-2, 2-naphthyl), 134.3 (d,
5JC,Pˆ3 Hz, C-4a, 2-naphthyl), 144.5 (d, JC,Pˆ5.3 Hz,
2
3
C-5), 159.7 (d, JC,Pˆ2.3 Hz, –CO2CH3), 164.7 (d,
1JC,Pˆ52.7 Hz, C-4), 192.5 (d, JC,Pˆ55.7 Hz, C-2); MS
1
(EI, 70 eV) m/z 326 (100) [M]ϩ, 295 (2.5) [M–CH3O]ϩ,
279 (12.0) [M–CH3O2]ϩ), 155 (39.1) [Naph-CO]ϩ, 127
(27.6) [C10H7]ϩ); C19H19O3P (326.33).
Ethyl
4-tert-butyl-2-(4-methylphenyl)-1,3-oxaphos-
phole-5-carboxylate (14i). Yield: 66 mg (39%), (Method
A); IR (CHCl3) n 1715 cmϪ1 (vs, CO); 31P NMR (CDCl3)
1
3
d 111.9 (s); H NMR (CDCl3) d 1.64 (t, 3H, JH,Hˆ7.2 Hz,
–CO2CH2CH3), 1.72 [d, 9H, 4JH,Pˆ1.9 Hz, –C(CH3)3], 2.58
Ethyl
4-tert-butyl-2-phenyl-1,3-oxaphosphole-5-car-
3
boxylate (14f). Yield: 100 mg (89%), (Method B), IR
(s, 3H, p-CH3, aryl), 4.61 (q, 2H, JH,Hˆ7.2 Hz,

70
S. G. Ruf et al. / Tetrahedron 56 (2000) 63–70
–CO2CH2CH3], 7.39, 7.97 (each d, 4H, aryl-H); 13C NMR
(CDCl3) d 14.2 (s, –CO2CH2CH3), 21.4 (s, p-CH3, aryl),
225 e/nm3 and a minimum of Ϫ147 e/nm3. Anisotropic
thermal parameters of non-hydrogen atoms, atomic coordi-
nates, bond lengths and bond angles involving hydrogen
atoms will be deposited at the Cambridge Crystallographic
Centre (CCDC 12 46 78).
31.3
[d,
3JC,Pˆ11.2 Hz,
–C(CH3)3],
33.7
(d,
2JC,3Pˆ15.2 Hz, –C(CH3)3], 61.1 (s, –CO2CH2CH3), 124.5
(d, JC,Pˆ12.9 Hz, o-C, aryl), 129.4 (s, m-C, aryl), 131.2 (d,
2JC,Pˆ12.9 Hz, ipso-C, aryl), 139.8 (d, JC,Pˆ4.0 Hz, p-C,
5
2
3
aryl), 143.9 (d, JC,Pˆ5.6 Hz, C5), 158.9 (d, JC,Pˆ1.6 Hz,
1
–CO2CH2CH3), 163.5 (d, JC,Pˆ53.0 Hz, C4), 192.5 (d,
Acknowledgements
1JC,Pˆ55.4 Hz, C2); MS (EI, 70 eV) m/z 304 (100.0)
[M]ϩ, 259 (6.7) [M–C2H5O]ϩ, 243 (52.0) [M–C2H5O2]ϩ,
91 (12.0) [Me-C6H4]ϩ; HRMS Calcd. for C17H21O3P:
304.1228. Found: 304.1233.
We are grateful to the Fonds der Chemischen Industrie for a
postgraduate grant (S. G. R.). We are also indebted to the
Deutsche Forschungsgemeinschaft (Graduiertenkolleg
“Phosphor als Bindeglied verschiedener chemischer
Disziplinen“) for generous financial support.
Ethyl
4-(1,1-dimethylpropyl)-2-phenyl-1,3-oxaphos-
phole-5-carboxylate (14j). Yield: 100 mg (85%), (Method
B); IR (CHCl3): n 1716 cmϪ1 (vs, CO); 31P NMR (CDCl3) d
1
3
117.1 (s); H NMR (CDCl3) d 0.81 (t, 3H JH,Hˆ7.2 Hz,
References
3
–CMe2CH2CH3), 1.42 (t, 3H, JH,Hˆ7.2 Hz, –CO2CH2CH3),
4
¨
1.46 [d, 6H, JH,Pˆ2.2 Hz, –C(CH3)2-CH2CH3], 1.94 [q, 2H,
1. Lober, O.; Regitz, M. Part 143. Main Group Chemistry News
3JH,Hˆ7.2 Hz, –C(CH3)2CH2CH3], 4.39 (q, 2H, 3JH,Hˆ7.2 Hz,
–CO2CH2CH3), 7.40–7.90, (each m, 5H, aryl-H); 13C NMR
(CDCl3) d 9.7 (s, –CMe2CH2CH3), 14.5 (s, –CO2CH2CH3),
1999, 7 in press.
2. Heinicke, J.; Tzschach, A. Phosphorus, Sulfur 1985, 25, 345.
3. Dotz, K. H.; Tiriliomis, A.; Harms, K. J. J. Chem. Soc., Chem.
¨
3
29.7 [d, JC,Pˆ12.9 Hz, –C(CH3)2CH2CH3], 34.7 [d,
Commun. 1989, 788.
2
3JC,Pˆ5.6 Hz, –C(CH3)2CH2CH3], 37.4 [d, JC,Pˆ13.7 Hz,
4. Dotz, K. H.; Tiriliomis, A.; Harms, K. Tetrahedron 1993, 49,
¨
–C(CH3)2-CH2CH3], 61.2 (s, –CO2CH2CH3), 124.9 (d,
3JC,Pˆ12.0 Hz, o-C, phenyl), 129.0 (s, m-C, phenyl), 129.9
5577.
5. Mack, A.; Ruf, S. G.; Regitz, M., University of Kaiserslautern,
unpublished results.
6. Mack, A. Thesis, University of Kaiserslautern, 1998.
7. Rosch, W.; Richter, H.; Regitz, M. Chem. Ber. 1987, 120, 1809.
8. Marino, J.; Osterhout, M.; Price, A.; Sheehan, S.; Padwa, A.
Tetrahedron Lett. 1994, 35, 849.
5
2
(d, JC,Pˆ3.0 Hz, p-C, phenyl), 134.1 (d, JC,Pˆ12.9 Hz,
2
ipso-C, phenyl), 144.6 (d, JC,Pˆ4.8 Hz, C5), 159.5 (s,
1
¨
–CO2CH2CH3), 162.3 (d, JC,Pˆ53.0 Hz, C4), 192.5 (d,
1JC,Pˆ54.6 Hz, C2); MS (EI, 70 eV) m/z 304 (84.3) [M]ϩ,
275 (19.2) [M–C2H5]ϩ, 259 (2.9) [M–C2H5O]ϩ, 243 (4.1)
[M–C2H5O2]ϩ, 105 (18.8) [Ph-CO]ϩ, 77 (13,6) [C6H5]ϩ, 51
(2,5) [C4H3]ϩ; C17H21O3P (304.33).
9. Grub, T. Thesis, University of Kaiserslautern, 1996.
10. Hornbuckle, S.; Padwa, A. Chem. Rev. 1991, 91, 263.
¨
11. Findeisen, K.; Konig, K.; Sundermann, R. In Houben-Weyl,
Crystal structure analysis of 14b
Methoden der Organischen Chemie, Hagemann, H., Ed.; Thieme:
Stuttgart, 1983; Vol. E4.
Crystal data. C16H19O4P, Mrˆ306.28, orthorhombic, space
group Pnma, aˆ912:6; bˆ699:8; cˆ2445:8 pm; aˆbˆ
gˆ90:00Њ; Vˆ1:5620ꢀ5† nm3; Zˆ4; dcalc:ˆ1:302 Mg/m3.
12. Potts, K. In 1,3-Dipolar Cycloaddition Chemistry, Padwa, A.,
Ed.; Wiley: New York, 1984; Vol. 2.
¨
13. Rosch, W.; Regitz, M. Angew. Chem., Int. Ed. Engl. 1984, 23,
900.
Data collection. The data collection was performed using
an automatic four circle diffractometer (Siemens P4)
at r.t. Crystal dimensions: 0:60×0:30×0:25 mm. The
measurements were made in the range 3:03ϽuϽ24:15Њ,
14. SHELXTL-Plus. Release 4.2, Siemens Analytical X-ray
Instruments, 1991.
¨
15. Markl, G. In Multiple Bonds and Low Coordination in Phos-
phorus Chemistry; Regitz, M., Scherer, O. J., Eds.; Thieme:
Stuttgart, 1990.
16. CRC Handbook of Chemistry and Physics, Lide, D. R., Ed.;
CRC: Boca Raton, 1992.
lˆ0:71073
MoKa
(graphite
monochromator),
Ϫ9ՅhՅ10, Ϫ8ՅkՅ7, Ϫ27ՅlՅ28, a total of 8041 reflec-
tions, of which 1319 were independent reflections.
17. Gattermann, L.; Wieland, H. Die Praxis des organischen
Chemikers; Walter de Gruyter: Berlin, 1982.
18. Sheldrick, G. M. Fortran Program for the Solution of Crystal
Structures from Diffraction Data, Institute for Organic Chemistry,
Structure solution and refinement. The structure was
solved using direct methods (SHELXS-86)18 and refined
with the full matrix least squares procedure against F2
(SHELXL-93).19 The anisotropic refinement converged at
R1ˆ0.0366 and wR2ˆ0.0982 [IϾ2s(I)] and R1ˆ0.0412,
wR2ˆ0.1011 [all data]. The difference Fourier synthesis on
the basis of the final structural model showed a maximum of
¨
University of Gottingen, 1986.
19. Sheldrick, G. M. Fortran Program for Crystal Structure
Refinement, Institute for Organic Chemistry, University of
¨
Gottingen, 1993.