Synthesis of 1-aryl-1,2,3,4,5,6-hexahydrophosphinine 1-oxides

Article abstract of DOI:10.1081/SCC-200036618

Possibilities for the synthesis of 1-(2,4,6-triisopropylphenyl-) 1,2,3,4,5,6-hexahydrophosphinine oxide (2) have been explored. The trivial method based on the hydrogenation of the corresponding dihydrophosphinine oxides (8a-e) was suitable only for the p

Full text of DOI:10.1081/SCC-200036618

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Synthesis of
1‐Aryl‐1,2,3,4,5,6‐hexahydrophos
1‐Oxides
György Keglevich a , Melinda Sipos a , Dóra Lengyel
a , Henrietta Forintos b , Tamás Körtvélyesi c ,
Tímea Imre d & László Tőke b
a Department of Organic Chemical Technology,
Budapest University of Technology and Economics,
1521, Budapest, Hungary
b Research Group of the Hungarian Academy of
Sciences at the Department of Organic Chemical
Technology, Budapest University of Technology and
Economics, Budapest, Hungary
c University of Szeged, Department of Physical
Chemistry, Szeged, Hungary
d Hungarian Academy of Sciences, Chemical
Research Center, Budapest, Hungary
Published online: 10 Jan 2011.
To cite this article: Gyrgy Keglevich , Melinda Sipos , Dra Lengyel , Henrietta
Forintos , Tams Krtvlyesi , Tmea Imre & Lszl Tke (2004) Synthesis of
1‐Aryl‐1,2,3,4,5,6‐hexahydrophosphinine 1‐Oxides, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry,
34:22, 4159-4169, DOI: 10.1081/SCC-200036618
To link to this article: http://dx.doi.org/10.1081/SCC-200036618

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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 22, pp. 4159–4169, 2004
Synthesis of 1-Aryl-1,2,3,4,5,6-
hexahydrophosphinine 1-Oxides
1,
Gyorgy Keglevich, Melinda Sipos, Dora Lengyel,
1
1
*
¨
Henrietta Forintos, Tamas Kortvelyesi, Tımea Imre,
´
2
3
4
´
¨
´
´
2
´
´
´
´
and Laszlo Toke
1Department of Organic Chemical Technology, Budapest University
of Technology and Economics, Budapest, Hungary
2Research Group of the Hungarian Academy of Sciences at the
Department of Organic Chemical Technology, Budapest University
of Technology and Economics, Budapest, Hungary
3University of Szeged, Department of Physical Chemistry,
Szeged, Hungary
4Hungarian Academy of Sciences, Chemical Research Center,
Budapest, Hungary
ABSTRACT
Possibilities for the synthesis of 1-(2,4,6-triisopropylphenyl-)1,2,3,4,5,6-
hexahydrophosphinine oxide (2) have been explored. The trivial method
based on the hydrogenation of the corresponding dihydrophosphinine
*
¨
Correspondence: Gyorgy Keglevich, Department of Organic Chemical Technology,
Budapest University of Technology and Economics, 1521, Budapest, Hungary;
E-mail: keglevich@mail.bme.hu.
4159
DOI: 10.1081/SCC-200036618
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

4160
Keglevich et al.
oxides (8a–e) was suitable only for the preparation of hexahydrophosphi-
nine oxides containing a trimethylphenyl or methylphenyl group on the
phosphorus atom (9a–c). The triisopropylphenyl product (2) was syn-
thesized by the stepwise reduction of the double bonds of starting material
1. Hence, the ring contraction side reaction, observed during the catalytic
hydrogenation, could be eliminated. The unusual reactivity was studied
by quantum chemical calculations.
Key Words: Dihydrophosphinine oxides; Reduction; Ring contraction
hexahydrophosphinine oxides; Theoretical calculations.
Organophosphorus compounds with sterically demanding substituents on
the phosphorus atom are of interest, because the stability and the reactivity of
the parent molecule are affected. Yoshifuji was successful in stabilizing low-
coordinated species by the introduction of the 2,4,6-trialkylphenyl substituent.[1]
Quin and Keglevich et al. could planarize the P-pyramid around the phosphorus
atom of phospholes by attaching a trialkylphenyl group to the heteroatom.[2–4]
As a consequence of this, the phospholes became aromatic. Phosphabicy-
clo[2.2.2]octenes with bulky substituents on the phosphorus atom were used
to study the mechanism of their fragmentation-related phosphorylations.[5,6]
Three of us discovered that P-trialkylphenyl cyclic phosphine oxides entered
into a novel reaction with acetylenic dicarboxylic esters to afford stabilized
phosphonium ylides.[7–9] The elaboration of this project requires additional
model compounds with an aryl group on the phosphorus atom.
In this article, the synthesis of a few 2,4,6-trialkylphenyl- and methyl-
phenyl-1,2,3,4,5,6-hexahydrophosphinine oxides is described.
The practical synthesis of 1-substituted 1,2,3,4,5,6-hexahydrophosphi-
nine oxides involves the hydrogenation of 1,2-dihydroposphinine oxides,[10]
or that of 3-phosphabicyclo[3.1.0]hexane 3-oxides[11] under appropriate con-
ditions. We found, however, that the reduction of the mixture of the double-
bond isomers (A and B) of 1-triisopropylphenyl-1,2-dihydrophosphinine
oxide (1)[12] with catalytically activated hydrogen furnished a 52–29–19%
mixture of three isomers of 3,4-dimethyl-2,3,4,5-tetrahydro-1H-phosphole
oxide 3 instead of the 3-methyl-hexahydrophosphinine oxide (2) required
(Scheme 1).[13] This surprising ring contraction is unique in the sphere of
reductive transformations. Another aryl-dihydrophosphinine oxide, the
di-tert-butyltolyl derivative, underwent the expected ring saturation smoothly
on hydrogenation.[13]
We decided to investigate how the conditions of the catalytic hydrogen-
ation affect the outcome of the reduction of 1. Assuming that the hydrochloric
acid formed during the reduction may catalyze the ring transformation, the

Synthesis of 1-Aryl-1,2,3,4,5,6-hexahydrophosphinine 1-Oxides
4161
Scheme 1.
hydrogenation of 1 was carried out in the presence of a base, such as 3 equiva-
lents of triethylamine or sodium hydroxide. Otherwise, the usual conditions of
temperature of (808C) and pressure (10 bar) were applied. We found, however,
that the presence of base in the reaction mixture had practically no effect on
the outcome. A similar result was obtained by running the reduction at
608C and 8 bar; the isomers of dimethyl-tetrahydro-1H-phosphole oxide (3)
were formed in 95% yield, and only traces of the expected product 2 could
be detected.
The preferred outcome in the hydrogenation of triisopropylphenyl-
dihydrophosphinine oxide 1 was studied by quantum chemical calculations.
First, the energy content and the geometry of the different isomers of the possi-
ble products (2 and 3) were calculated by the PM3 semiempirical method
implemented in MOPAC93.[14] The fully optimized geometries obtained
were used as the initial structures in HF/6-31Gꢀ// HF/6-31Gꢀ calculations
applying Gaussian98.[15] On the basis of the calculations, no significant differ-
ences were found between the energy contents of the 6- and the 5-membered
ring products (2 and 3, respectively). To simplify the situation, average values
are given for the different isomers. According to the PM3 method, the differ-
ence in the heat of formation (DDHf) was 20.99 kcal/mol, whereas using the
HF/6-31Gꢀ approach, the difference in the scaled (0.89 as scaling factor) zero
point vibrational energy (ZPVE) corrected energy (DDE0) was þ0.7 kcal/mol.
Placing a phenyl group instead of the triisopropylphenyl substituent on
the phosphorus atom of P-heterocycles 3 and 2, the differences were
22.5 kcal/mol (DDHf, PM3) and 23.3 kcal/mol (DDE0, HF/6-31Gꢀ). It
can be seen that according to the calculations, the P-aryl substituent has no
significant effect on the energy content. Hence, the reasons for the special
reactivity of dihydrophopshinie oxide 1 still remain speculative.
We next tried to synthesize hexahydrophosphinine oxide 2 by substi-
tution at phosphorus. Phosphinic ester 4[10] was converted by reaction with

4162
Keglevich et al.
phosphorus pentachloride into the corresponding phosphinic chloride, which
then gave the phosphinous chloride 5 by deoxygenation using trichlorosilane.
The reaction of 5 with arylmagnesium bromide, followed by oxidation of the
phosphine so obtained by hydrogen peroxide, led to an 88–12% mixture of
phosphinic ester 6 and phosphine oxide 2, both as mixtures of diastereomers
(Scheme 2).
The O-insertion probably occurred during the Grignard reaction. We have
also come across this in other cases,[16] and it is known from the literature.[17]
In the third approach, the unsaturated bonds of 1,2-dihydrophopshinine
oxide 1A were reduced in two steps. First, the electron-poor double bond
was saturated through hydroboration by dimethylsulfide-borane, to yield
tetrahydrophosphinine oxide 7 in 50% yield after column chromatography.
Catalytic hydrogenation of 7 provided a 55–45% diastereomeric mixture of
hexahydrophosphinine oxide 2 in 89% yield after purification (Scheme 3).
Intermediate 7 and product 2 were characterized by 31P, 13C, and 1H NMR
as well as by mass spectrometry.
Finally, three other aryl-dihydrophosphinine oxides (8a–c) were sub-
jected to hydrogenation at 808C and 10 bar. Both the trimethylphenyl-
hexahydrophosphinine oxide (9a) and the methylphenyl derivatives (9b and
9c) were obtained as about 71–29% mixtures of diastereomers and in good
yields (ca. 70%) after column chromatography (Scheme 4). The hexahydro-
1
phosphinine oxides (9a–c) were characterized by 31P, 13C, and H NMR as
well as by mass spectrometry.
In summary, new 1-aryl-1,2,3,4,5,6-hexahydrophosphinine oxides were
prepared. The basic procedure involves catalytic hydrogenation of the
corresponding 1,2-dihydrophosphinine oxides. Due to a ring contraction
side reaction, another route, the stepwise saturation of the double bonds of
the starting dihydrophosphinine oxide, was necessary for the synthesis of
the 2,4,6-triisopropylphenyl derivative.
Scheme 2.

Synthesis of 1-Aryl-1,2,3,4,5,6-hexahydrophosphinine 1-Oxides
4163
Scheme 3.
EXPERIMENTAL
The 31P, 13C, and 1H NMR spectra were obtained on a Bruker DRX-500
spectrometer operating at 202.4, 125.7, and 500 MHz, respectively. Chemical
shifts are downfield relative to 85% H3PO4 or TMS. The couplings are given
in Hz. Mass spectrometry was performed on a ZAB-2SEQ instrument. The
starting dihydrophosphinine oxides 1 and 8a were prepared as described
earlier.[12,17,18]
General Procedure for the Preparation of
1,2,3,4,5,6-Hexahydrophosphinine 1-Oxides (9a–c)
A solution of 0.79 mmol of the 75–25% isomeric mixture of 3- and
5-methyl-1,2-dihydrophosphinine 1-oxide (8a–c) in 30 mL of methanol and
Scheme 4.

4164
Keglevich et al.
0.2 g of 10% Pd/C was measured in an autoclave equipped with a magnetic
stirrer. The hydrogenation was carried out at 808C and 10 bar for 14 hr.
The suspension was filtered and the solvent was evaporated. Purification of
the crude product by column chromatography (silica gel, 3% methanol in
chloroform) afforded product (9a–c).
2,4,6-Trimethylphenyl-3-methyl-1,2,3,4,5,6-
hexahydrophosphinine 1-Oxides (9a)
Yield: 68%, as a 75–25% mixture of 9a1 and 9a2 isomers; HRMS
(M þ H)þfound ¼ 251.1524; C13H19OP requires 251.1565.
9a1
31P NMR (CDCl3) d 39.5; 13C NMR (CDCl3) d 21.0 (p-CH3), 21.5
(1J ¼ 4.6, C5), 23.6 (1J ¼ 12.9, C3–CH3), 23.7 (1J ¼ 3.8, o-CH3), 30.7
(1J ¼ 3.6, C3), 31.8 (1J ¼ 63.7, C6), 34.5 (1J ¼ 3.5, C4), 39.9 (1J ¼ 61.7,
1
1
0
0
0
C2), 126.8 ( J ¼ 93.3, C1 ), 131.2 ( J ¼ 10.7, C3 ), 140.9 (C4 ), 141.7
1
1
1
0
( J ¼ 9.7, C2 ); H NMR (CDCl3) d 1.06 (dd, J ¼ 6.5, 3H, C3–Me), 2.27
0
(s, 3H, C4 –Me), 2.63 (s, 6H, C2 –Me), 6.88 (s, 2H, ArH).
0
9a2
31P NMR (CDCl3) d 39.3; 13C NMR (CDCl3) d 21.1 (p-CH3), 21.5
(1J ¼ 4.6, C5), 23.7 (1J ¼ 3.8, o-CH3), 25.0 (1J ¼ 14.8, C3–CH3), 29.1
(1J ¼ 4.8, C3), 29.6 (1J ¼ 64.0, C6), 35.5 (1J ¼ 5.3, C4), 38.9 (1J ¼ 62.7,
1
1
0
0
0
C2), 126.9 ( J ¼ 93.3, C1 ), 131.4 ( J ¼ 11.0, C3 ), 141.2 (C4 ), 141.8
1
0
( J ¼ 10.4, C2 ).
2-Methylphenyl-3-methyl-1,2,3,4,5,6-hexahydrophosphinine
1-Oxides (9b)
Yield: 72%, as a 75–25% mixture of 9b1 and 9b2 isomers; HRMS
(M þ H)þfound ¼ 223.1221; C13H19OP requires 223.1252.
9b1
31P NMR (CDCl3) d 36.8; 13C NMR (CDCl3) d 21.1 (1J ¼ 4.2, o–CH3),
22.5 (1J ¼ 4.0, C5), 24.0 (1J ¼ 14.9, C3–CH3), 27.7 (1J ¼ 64.8, C6), 31.2
(1J ¼ 4.0, C3), 34.4 (1J ¼ 4.8, C4), 36.5 (1J ¼ 61.4, C2), 125.2 (1J ¼ 11.6,

Synthesis of 1-Aryl-1,2,3,4,5,6-hexahydrophosphinine 1-Oxides
4165
1
1
1
ꢀ
ꢀ
0
0
0
0
C5 ) , 129.3 ( J ¼ 92.6, C1 ), 130.2 ( J ¼ 11.2, C6 ), 131.3 ( J ¼ 2.3, C4 ),
132.0 ( J ¼ 9.8, C3 ) , 141.8 ( J ¼ 7.5, C2 ), ꢀtentative assignment; 1H
1
1
ꢀ
0
0
0
NMR (CDCl3) d 1.07 (dd, 3H, C3–Me), 2.72 (s, 3H, C2 –Me), 7.24–7.53
(m, 4H, ArH).
9b2
31P NMR (CDCl3) d 35.2; 13C NMR (CDCl3) d 20.6 (1J ¼ 5.6, C5), 21.1
(1J ¼ 4.2, o–CH3), 24.5 (1J ¼ 14.9, C3–CH3), 28.7 (1J ¼ 62.3, C6), 33.2
(1J ¼ 9.4, C3), 35.2 (1J ¼ 4.8, C4), 35.8 (1J ¼ 64.5, C2), 129.4 (1J ¼ 11.5,
1
1
1
ꢀ
ꢀ
ꢀ
0
0
0
0
C5 ) , 130.0 ( J ¼ 10.9, C6 ) , 131.3 ( J ¼ 2.3, C4 ), 132.0 ( J ¼ 9.8, C3 ),
1
ꢀ
0
141.5 ( J ¼ 7.9, C2 ), tentative assignment.
4-Methylphenyl-3-methyl-1,2,3,4,5,6-hexahydrophosphinine
1-Oxides (9c)
Yield: 74%, as a 64–36% mixture of 9c1 and 9c2 isomers; HRMS
(M þ H)þfound ¼ 223.1232; C13H19OP requires 223.1252.
9c1
31P NMR (CDCl3) d 34.8; 13C NMR (CDCl3) d 20.8 (p–CH3), 21.6
(1J ¼ 4.0, C5), 23.3 (1J ¼ 14.6, C3–CH3), 26.2 (1J ¼ 65.4, C6), 30.3
(1J ¼ 3.6, C3), 33.8 (1J ¼ 5.0, C4), 35.1 (1J ¼ 63.4, C2), 128.3 (1J ¼ 95.8,
1
1
1
ꢀ
ꢀ
0
0
0
0
C1 ), 128.9 ( J ¼ 11.1, C2 ) , 129.1 ( J ¼ 9.5, C3 ) , 141.3 ( J ¼ 2.6, C4 ),
ꢀtentative assignment; 1H NMR (CDCl3) d 1.08 (dd, 3H, C3–Me), 2.42
0
(s, 3H, C4 –Me), 7.28–7.70 (m, 4H, ArH).
9c2
31P NMR (CDCl3) d 33.5; 13C NMR (CDCl3); d 20.3 (1J ¼ 5.6, C5), 20.8
(p–CH3), 24.1 (1J ¼ 15.0, C3–CH3), 26.8 (1J ¼ 66.4, C6), 27.9 (1J ¼ 4.6,
1
1
1
ꢀ
0
C3), 33.8 ( J ¼ 5.0, C4), 36.0 ( J ¼ 64.9, C2), 128.6 ( J ¼ 11.5, C2 ) , 129.4
1
1
ꢀ
ꢀ
0
0
( J ¼ 9.6, C3 ) , 141.3 ( J ¼ 2.6, C4 ), tentative assignment.
Hydrogenation of the double bond isomers (A and B) of triisopropyl-
phenyl-1,2-dihydrophosphinine oxide (1) under similar conditions led to a
29–52–19% mixture of dimethyl-2,3,4,5-tetrahydro-1H-phosphole 1-oxide 3.

4166
Keglevich et al.
Attempted Conversion of 1-Ethoxy-hexahydrophosphinine
1-Oxide 4 to 1-Triisopropylphenyl-hexahydrophosphinine
1-Oxide (2)
To 0.89g (5.0mmol) of the diastereomers of ethoxy-hexahydrophosphi-
nine 1-oxide (4) in 20mL of dry chloroform, 1.1 g (5.3mmol) of phosphorus
pentachloride was added. The mixture was stirred at room temperature and
then at the boiling point for 5 hr. The volatile components were removed in
vacuo to provide the corresponding phosphonic chloride in quantitative yield.
To 0.84 g (ꢀ5.0 mmol) of phosphonic chloride (from the previous reac-
tion) in 20 mL of dry dichloromethane, 0.25 mL (2.0 mmol) phenylsilane
was added in nitrogen atmosphere. The contents of the flask were stirred at
the boiling point for 5.5 hr under nitrogen. The reaction mixture was concen-
trated in vacuo to give 0.84 g (ꢀ100%) phosphinic chloride 5.
To 0.74 g (ꢀ5.0 mmol) of phosphinic chloride (5) in 15 mL of dry tetra-
hydrofuran was added 5.5 mmol of arylmagnesium bromide [prepared from
0.13 g (5.5 mmol) of magnesium and 1.55 g (5.5 mmol) of 2,4,6-triisopro-
pyl-1-bromobenzene in 15 mL of tetrahydrofuran] dropwise at 08C, and the
mixture was then stirred at room temperature for 14 hr. The solvent was
evaporated in vacuo and the residue was taken up in a mixture of 15 ml of
chloroform and 5 mL of water containing 3 drops of hydrochloric acid. The
organic phase was separated and dried (Na2SO4). Evaporation of the solvent
led to 2.1 g (64%) of crude arylphosphine.
2.1 g (6.6 mmol) of arylphosphine in 50 mL chloroform was treated
with 1.5 mL (ꢀ13.2 mmol) of 30% hydrogen peroxide at 08C. The cooling
bath was removed and the mixture was stirred at 268C for 2 hr. Excess of
the peroxide was removed by extraction with 3 ꢁ 10 mL of water. The chloro-
form phase was dried (Na2SO4), and the solvent was evaporated to afford
a mixture (2.0 g) of arylphosphine oxide 2 (125, 31P NMR [CDCl3) d 32.9
(63%) and 39.3 (37%)] and arylphosphinate 6 (88%).
Repeated column chromatography (3% methanol in chloroform, silica gel)
furnished 1.7 g (88%) of 6 in þa pure form. 31P NMR (CDCl3) d 53.7 (53%) and
54.2 (47%); HRMS (M þ H)found ¼ 351.2421, C21H36O2P requires 351.2453.
The Two-Step Conversion of
1-Triisopropylphenyl-1,2-dihydrophosphinine
1-Oxide (1A) to Hexahydrophosphinine 1-Oxide (2)
A. 4-Chloro-5-methyl-1-(2,4,6-triisopropylphenyl)
1,2,3,6-tetrahydrophosphinine 1-oxide (7)
To a solution of 0.5 g (1.4 mmol) of 1-triisopropylphenyl-dihydrophos-
phinine 1-oxide (1A) in 30 mL of CH2Cl2 was added 1.1 mL (2.2 mmol)

Synthesis of 1-Aryl-1,2,3,4,5,6-hexahydrophosphinine 1-Oxides
4167
2 M borane-dimethyl sulfide in THF. The mixture was stirred at 248C for
15 min and then at 408C for 24 hr. After completion of the reaction, 1.4 mL
of H2O was added, and the contents of the flask were stirred for 15 min.
The mixture was filtered and the organic phase separated and dried
(Na2SO4). The crude product obtained after evaporating the solvent was puri-
fied by column chromatography (silica gel, 3% MeOH in CHCl3) to give
0.25 g (36%) 7; 31P NMR (CDCl3) d 34.1; 13C NMR (CDCl3) dC 23.2
1
a
ꢀ
0
0
( J ¼ 9.7, C5–CH3), 23.9 (C2 –CH(CH3)2), 25.3 (C4 –CH(CH3)2) , 25.4
1
1
ꢀ
0
(C6 –CH(CH3)2) , 29.4 ( J ¼ 65.8, C6), 30.3 ( J ¼ 3.9, orto-CH(CH3)2),
30.6 (1J ¼ 6.4, C3), 34.4 (para-CH(CH3)2), 38.9 (1J ¼ 64.3, C2), 123.1
1
1
1
0
0
( J ¼ 11.1, C3 ), 124.6 ( J ¼ 5.9, C5), 127.3 ( J ¼ 11.9, C4), 152.5 (C4 ),
1
1
153.9 ( J ¼ 11.1, C2 ), ꢀtentative assignment; H NMR (CDCl3) d 1.21–
1.34 (m, 18H, CH(CH3)2), 1.94 (s, 3H, C5–Me), 7.15 (s, 2H, ArH); FAB;
(M þ H)þfound 367.1904, C21H33ClOP requires 367.1958 for the 35Cl isotope.
0
B. 1-(2,4,6-triisopropylphenyl-)1,2,3,4,5,6-hexahydrophosphinine
1-oxide (2)
7 was hydrogenated, as described for the 8 ! 9 transformation. Column
chromatography of the crude product afforded 0.08 g (89%) ofþ2 as a 55–45 %
mixture of 21 and 22 diastereomers. HR-FAB; (M þ H)found 335.2472,
C21H36OP requires 335.2504; 1H NMR (CDCl3) d 1.16–1.31 (m, 18H,
CH(CH3)2), 1.91 (s, 3H, C3–Me), 7.10 (s, 2H, ArH).
Isomer 21
31P NMR (CDCl3) d 38.4; 13C NMR (CDCl3) d 20.2 (1J ¼ 4.7, C5), 22.9
1
ꢀ
ꢀ
0
0
( J ¼ 9.9, C3–CH3), 23.8 (C2 –CH(CH3)2) , 25.1 (C4 –CH(CH3)2) , 25.3
1
1
ꢀ
0
(C6 –CH(CH3)2) , 30.2 ( J ¼ 4.5, C3), 30.8 ( J ¼ 4.3, orto-CH(CH3)2), 32.5
(1J ¼ 64.1, C6), 33.4 (1J ¼ 6.3, C4), 34.2 (para-CH(CH3)2), 40.1
1
1
1
0
0
0
( J ¼ 62.1, C2), 121.1 ( J ¼ 96.1, C1 ), 122.9 ( J ¼ 10.6, C3 and C5 ), 151.9
1
1
ꢀ
0
0
0
( J ¼ 2.6, C4 ), 153.6 ( J ¼ 10.6, C2 and C6 ), tentative assignment.
Isomer 22
31P NMR (CDCl3) d 37.3; 13C NMR (CDCl3) d 18.9 (1J ¼ 5.1, C5), 23.8
ꢀ
ꢀ
ꢀ
0
0
0
(C2 –CH(CH3)2), 25.1 (C4 –CH(CH3)2), 25.2 (C6 –CH(CH3)2), 27.1
(1J ¼ 15.6, C3–CH3), 28.7 (1J ¼ 68.1, C6), 30.1 (1J ¼ 4.5, C3), 30.8
(1J ¼ 4.3, orto-CH(CH3)2), 32.3 (1J ¼ 9.7, C4), 34.2 (para-CH(CH3)2), 40.1
1
1
1
0
0
0
( J ¼ 62.1, C2), 123.0 ( J ¼ 10.9, C3 and C5 ), 125.1 ( J ¼ 92.2, C1 ), 151.9
1
1
ꢀ
0
0
0
( J ¼ 2.6, C4 ), 154.3 ( J ¼ 10.9, C2 and C6 ), tentative assignment.

4168
Keglevich et al.
ACKNOWLEDGMENTS
The authors are grateful for the OTKA support of the work (Grant No.
T 042479). The advice of Professor Emeritus Dr Harry R. Hudson (London
Metropolitan University) is appreciated.
REFERENCES
1. Yoshifuji, M. Protecting groups for stabilisation of unusual organophop-
shorus compounds. Main Group Chem. News 1998, 6, 20.
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Received in the UK March 30, 2004