Reduction of phosphine oxides to phosphines with the InBr3/TMDS system

Article abstract of DOI:10.1016/j.tet.2012.02.063

An efficient method for the reduction of phosphine oxide derivatives into their corresponding phosphines is described. The system InBr₃/TMDS allows the reduction of different secondary and tertiary phosphine oxides as well as aliphatic and aromatic phosphine oxides.

Full text of DOI:10.1016/j.tet.2012.02.063

Tetrahedron 68 (2012) 3151e3155
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Reduction of phosphine oxides to phosphines with the InBr3/TMDS system
a
a
b
c
a,
*
ꢀ
ꢀ
Leyla Pehlivan , Estelle Metay , Dominique Delbrayelle , Gerard Mignani , Marc Lemaire
a
ꢁ
ꢀ
Laboratoire de Catalyse et Synthese Organique, Institut de Chimie et Biochimie Moleculaires et Supramoleculaires (ICBMS), CNRS, UMR5246, Universite Lyon 1,
43 Boulevard du 11 Novembre 1918, Bat CPE, 69622 Villeurbanne, France
b Minakem SAS, 145 Chemin des Lilas, 59310 Beuvry la Foret, France
c Rhodia, Lyon Research center, 85, Avenue des Freres Perret, BP 62, 69192 Saint-Fons Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient method for the reduction of phosphine oxide derivatives into their corresponding phos-
phines is described. The system InBr3/TMDS allows the reduction of different secondary and tertiary
phosphine oxides as well as aliphatic and aromatic phosphine oxides.
Received 3 November 2011
Received in revised form 14 February 2012
Accepted 26 February 2012
Available online 3 March 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Reduction
Phosphine oxide
TMDS
InBr3
Phosphine
1. Introduction
associated with activated carbon at 350 ꢀC,11 SiCl4 with a metal12
and sulfur derivatives13 can be cited. Another way to prepare
Tertiary and secondary phosphines are important compounds in
organic synthesis. They are widely used for metal ligation since
many transition metal complexes contain phosphines and
diphosphines as ligands.1 These ones used as catalysts allow hy-
drogenation, hydroformylation, hydrocyanation, allylic sub-
stitution, hydrosilylations or palladium-catalyzed coupling
reactions. Phosphines such as triphenylphosphine (TPP), for ex-
ample, are also used in various types of reactions: Wittig,2 Mitsu-
nobu,3 Appel,4 Staudinger5 reactions etc. Triphenylphosphine oxide
(TPPO) is generated as a by-product in these reactions and is con-
sidered as a waste even if some progress was made for a catalytic
version of these reactions.6 Thus, finding an appropriate method to
convert phosphine oxides derivatives into their corresponding
phosphines appears to be a good solution. Indeed the initial
phosphine could be regenerated and reused. Reduction of triphe-
nylphosphine oxide has been performed under different condi-
tions. Aluminum hydrides7 can be employed for this
transformation but they are not appropriate for the industry: they
are expensive, highly reactive with air and water, difficult to handle.
Other systems have been developed for the direct reduction of
TPPO. SmI2/HMPA,8 TiCp2Cl2/Mg,9 Bi/TiO2,10 hydrocarbon
phosphines is the electroreduction of triphenylphosphine ox-
ides.14,15 The indirect reduction of TPPO to TPP via the corre-
sponding triphenylphosphine dichloride has also been described. It
includes a step with a chlorination agent. Then phosgene,16 oxalyl
chloride associated with PbBr2 or other additives17 were used and
the dichloride derivative requires to be reduced with a metal as
sodium or aluminum. From a cost and/or safety point of view these
cited methods are not recommended.
19
Finally, silanes such as Ph2SiH,6 HSiCl3,18 (EtO)3SiH/Ti(OiPr)4
have been used and give the expected phosphines with good
yields, but unfortunately several silanes have been demonstrated
harmful since they generate a dangerous, pyrophoric and toxic
20
SiH4
gas. As a consequence, more stable hydrosiloxanes
(SieOeSi) are considered as being highly interesting as the ulti-
mate waste is silica. Among these derivatives, PMHS (Poly-
methylhydrosiloxane), a 40-unit polymeric chain, was efficiently
used with 1 equiv of Ti(OiPr)4 by Lawrence to give phosphines.19
TMDS (1,1,3,3-tetramethyldisiloxane) (Scheme 1) also constitutes
a safe siloxane, which derives from a by-product of the industry and
can be recycled for the water-repellent treatment of materials.
* Corresponding author. E-mail address: marc.lemaire@univ-lyon1.fr (M.
Scheme 1. TMDS structure.
Lemaire).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.02.063

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L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155
In that way our group previously described the reduction of
reduction of TPPO was tested in methylcyclohexane (MCH) (Table
2). In toluene at 100 ꢀC, the reaction was complete (Table 2, entry
1). However in MCH at 60 ꢀC the TPP was not obtained and only the
initial TPPO was observed (Table 2, entry 2). During the previous
study realized on the Ti/TMDS system, the formation of water
during the reaction was supposed because the addition of dehy-
drating agent like sodium sulfate allowed a better conversion. This
was in agreement with the proposed mechanism. Thus, the addi-
tion of Na2SO4 was considered but did not improve the reduction
since the starting material remained intact (Table 2, entry 3). On the
opposite of the titanium cluster it is known that InBr3 is more
stable. When temperature was increased to 100 ꢀC and without the
presence of a desiccant, the formation of the desired product was
observed with a conversion of 79% (Table 2, entry 4). This result is
however less interesting than the reduction in toluene. Reaction
performed without solvent did not allow the formation of the
phosphine (Table 2, entry 5).
tertiary and secondary phosphine oxides with the system Ti(OiPr)4/
TMDS (Scheme 2).21
Scheme 2.
A mechanistic insight has revealed the presence of silicon rad-
ical species. Moreover, Sakai22 recently described the reduction of
different functions in the presence of catalytic amount of InBr3 and
silane. In these papers they propose the formation of radical spe-
cies. As a consequence, it was interesting to study the reduction of
phosphine oxide with the association of TMDS/Indium.
Table 2
Comparison with previous conditions of reduction
2. Results and discussion
Herein, we describe the efficient reduction of phosphine oxide
derivatives by the catalytic system InBr3/TMDS. We started our
investigation by testing different sources of indium with PMHS or
TMDS as hydride sources. Triphenylphosphine oxide was consid-
ered as the model substrate. All tests were performed with 1 mol %
of indium III catalyst (Table 1). At 100 ꢀC with TMDS and indium
triflate, the reduction of TPPO occurred with a conversion of 28%
(Table 1, entry 1). Under the same conditions InBr3 gave a complete
conversion into the desired TPP (Table 1, entry 2). In order to see the
temperature effect on this reaction, the temperature was decreased
to 60 ꢀC. We then observed a slight conversion of 10% after 18 h and
after 3 days the reaction was still not complete (Table 1, entry 3). A
test with PMHS (40 unit polymeric chain) under the optimal con-
ditions allowed us to eliminate the PMHS as a potential reducing
agent for this reduction since noTPP was obtained (Table 1, entry 4).
This observation could be in agreement with the formation of a silyl
radical species. Indeed the accessibility of the formed radical on
a polymeric structure is limited. Other sources of indium such as
indium acetate (Table 1, entry 5) or indium acetylacetonate (Table 1,
entry 6) did not allow the conversion of TPPO into the attempted
TPP. One more experiment was run to reduce triphenylphosphine
oxide with 5 mol % of copper triflate instead of indium complexes.
Only 80% conversion was reached in 23 h. This lower reactivity was
confirmed again with the reduction of tributylphosphine oxide.
After 20 h only 28% conversion was observed.
Entry
Solvent
SieH (equiv)
T (ꢀC)
Desiccant
Conv.a (%)
1
2
3
4
5
Toluene
MCH
MCH
MCH
d
3 (1.5)
2.5 (1.25)
3 (1.5)
3 (1.5)
3 (1.5)
100 ꢀC
60 ꢀC
ee
>99%
0
0
79%
0
ee
60 ꢀC
Na2SO4 (10%)
ee
100 ꢀC
100 ꢀC
ee
a
Conversions were determined by 31P NMR after 18 h.
When decreasing the SieH quantity (1 mol/mol of substrate) in
18 h the conversion reached only 90% whereas with 1.5 mol/mol
the conversion was complete in 7 h.
Best conditions (Table 2, entry 1) were then applied on different
phosphine oxide derivatives.
The scope and limitation of the system was then explored. Tri-
phenylphosphine oxide was efficiently reduced after 7 h of reaction
into the corresponding triphenylphosphine (Table 3, entry 1). The
methyldiphenylphosphine oxide was also reduced completely and
gave after 18 h the corresponding phosphine. However this phos-
phine is readily re-oxidized during the work-up, therefore it was
necessary to protect it into phosphine borane. The corresponding
phosphine borane was isolated with a quantitative yield (Table 3,
entry 2). The system InBr3/TMDS allows the reduction of phosphine
oxide derivatives, which contain a methoxy group since the sub-
strate 1c was totally converted into 2c and isolated with a quanti-
tative yield as the borane phosphine (Table 3, entry 3). However if
the substrate contains a double bond, this one is also reduced. In-
deed for the reduction of compound 1d both phosphine oxide and
double bond were reduced to give the phosphine 2d. Although it
was reduced with 98% conversion, 2d was isolated with only 21%
yield (Table 3, entry 4). Indeed this product, even after protection,
was not stable and was quickly re-oxidized. In order to check the
selectivity between phosphine oxide the CeC double bond, reaction
was performed with 1 mol/mol of substrate. After 18 h, the for-
mation of 33% of the reduced phosphine oxide was noticed by NMR
(keeping the double bond).
Table 1
Reduction of TPPO with different sources of indium
Entry
Indium
SieH
Temperature
Conv.a (%)
1
2
3
4
5
6
In(OTf)3
InBr3
InBr3
InBr3
In(OAc)3
In(acac)3
TMDS
TMDS
TMDS
PMHS
TMDS
TMDS
100 ꢀC
100 ꢀC
60 ꢀC
100 ꢀC
100 ꢀC
100 ꢀC
28%
>99%
10% (50%)b
0
<5%
0
a
Conversions were determined by 31P NMR after 18 h except for entry 2 only 7 h
However at higher conversions the CeC double bond was re-
duced. Same observation concerning the double bond was noticed
on the 3-methyl-1-phenyl-2-phospholene oxide 1e since after 40 h
both oxide and double bond were reduced. 2e was isolated with
95% yield (Table 3, entry 5). Concerning mechanistic consideration
the formation of a radical species with the indium system seems
correct as soon as the double bonds are reduced at the same time
were needed.
b
After 3 days.
Based on these results InBr3 was kept as catalyst with TMDS as
hydride source. In order to compare these results with those ob-
tained previously with the system Ti(OiPr)4/TMDS/Na2SO4,

L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155
3153
Table 3
Application on different phosphine oxides
Entry
1
Substrates
Products
Reaction time (h)
Conv. (%)a
Isolated yield (%)b
1a
1b
2a
2b
7
>99%
84%
2
3
4
5
18
>99%
>99%
>98%
>95%
>99%
1c
1d
1e
2c
2d
2e
18
18
40
>99%
21%c
95%d
6
7
1f
2f
22
22
72%e
55%
80%
f
1g
2g
>99%
8
9
1h
1i
2h
2i
24
30
0%
ee
>95%
>99%
10
11
12
1j
1k
1l
2j
2k
2l
18
18
18
86%
80%
96%
70%
>99%
>92%
13
1m
2m
17
>99%
ND
Conditions: Substrate (5 mmol), InBr3 (1 mol %), TMDS (1.5 equiv), Toluene (1 M), 100 ꢀC.
a
Conversions were determined by 31P NMR.
Yield after flash chromatography.
Reoxidation of the phospshine was observed.
After 18 h phosphine oxide was completely reduced and the double bond was partially reduced.
Reaction required 10 mol % of InBr3.
b
c
d
e
f
2 mol % of InBr3 and 3 equiv of TMDS were used.
and no products come from hydrosilylation were observed. The
occurred and only the starting material was detected. After 22 h
and a conversion of 72%, product 2f was isolated with 55% (Table 3,
entry 6). Conditions of reaction were then applied on dppp(O) 1g
and the corresponding dppp 2g was obtained with a total conver-
sion and isolated with 80% (Table 3, entry 7). It is interesting to
radical-based hydrosilylation of carbonecarbon double bonds was
already described with silane.23 The reduction of cyclo-
hexyldiphenylphosphine oxide 1f was particular since it required
10 mol % of InBr3. When 1 mol % of catalyst was used no reaction

3154
L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155
notice that no conversion was observed on dppb(O) 1h. Indeed
dppb(O) is not soluble in toluene and in this way it prevents the
reaction to occur (Table 3, entry 8). In MCH the same problem of
solubility was noticed and no conversion was observed. The re-
duction was then tested on aliphatic phosphine oxides. A first
conclusive test on tricyclohexylphosphine 1i allowed us to con-
clude that both aromatic and aliphatic phosphine oxides could be
reduced. Then 2i was isolated with 95% yield after a conversion of
95% (Table 3, entry 9). Tri-n-butylphosphine oxide 1j was converted
into 2j with 86% conversion and isolated with a good yield of 80%
(Table 3, entry 10). With a longer alkyl chain (C8), the conversion
was total and 1k was isolated with 96% yield to give the protected
phosphine borane 2k (Table 3, entry 11).The reduction of secondary
phosphine oxides was also considered. Conditions were applied on
diphenylphosphine oxide 1l and after 18 h 92% of 1l was converted.
The diphenylphosphine was then protected and isolated with 70%
yield (Table 3, entry 12). As for compound 2d, the protective step is
delicate since the reoxidation is fast.
Finally, the reaction can also be applied for the reduction of
phosphinic acids. An example on diphenylphosphinic acid 1m was
done and was successfully converted into 2m (Table 3, entry 13).
From all data in Table 3, the system TMDS/InBr3 can be com-
pared to the results obtained with TMDS/Ti(OiPr)4. More precisely,
secondary, tertiary phosphine oxide and diphosphine oxide can be
reduced. The only noticed difference was the difficulty to reduce
the diphenylphosphinobutane oxide, which is not soluble in the
reaction media. Several experiments were also made for the re-
duction of BINAP oxide but no reaction occurred, probably because
of the low solubility of BINAP oxide in toluene and in most of low
polar organic solvents.
argon atmosphere. The reaction mixture was stirred at 100 ꢀC
during 7e40 h depending on the substrate (the reaction was
monitored by 31P NMR). After complete consumption of the reagent
the mixture was kept under argon in the sealed tube and cooled to
0 ꢀC. A solution of BH3.SMe2 (2 M in THF, 1 equiv) was then slowly
added. After 1 h at room temperature, 31P NMR analysis of an ali-
quot indicates complete conversion to phosphine borane adduct.
The crude was poured in an erlenmeyer flask and silica gel was
carefully added while stirring. When silica gel was added in the
reaction mixture, a slightly exothermic reaction was observed. The
reaction mixture was then filtered on silica gel and washed several
times with ethyl acetate. After evaporation of the ethyl acetate, the
residue was purified by flash chromatography on silica gel with
pure cyclohexane to afford the desired phosphineeborane.
Compounds 2a, 2g, 2h are purified without the BH3 protection.
4.2.1. Triphenylphosphine [603e35-0] 2a. White solid. 1H NMR
(300 MHz, CDCl3):
d
¼7.30e7.36 (m, 15H). 13C NMR (75 MHz, CDCl3):
d
¼137.5 (s, JCP¼10.5 Hz), 134.1 (d, JCP¼19.1 Hz), 128.9 (d,
JCP¼19.1 Hz), 128.8 (s). 31P NMR (121 MHz, CDCl3):
¼-4.3.
d
4.2.2. Methyldiphenylphosphine-borane [54067-17-3] 2b. Colorless
oil. 1H NMR (300 MHz, CDCl3):
d
¼7.51e7.58 (m, 4H), 7.26e7.34 (m,
6H), 1.72 (d, J¼10.2 Hz, 3H). 13C NMR (75 MHz, CDCl3):
¼131.9 (d,
d
JCP¼9.2 Hz), 131.3, 130.2, 129.0 (d, JCP¼9.8 Hz), and 12.0 (d,
JCP¼40 Hz). 31P NMR (121 MHz, CDCl3):
¼11.2.
d
4.2.3. Diphenyl(methoxymethyl)phosphineeborane 2c. White oil. 1H
NMR (300 MHz, CDCl3):
¼7.73e7.80 (m, 4H), 7.42e7.54 (m, 6H),
4.27 (s, 2H), 3.42 (s, 3H). 13C NMR (75 MHz, CDCl3):
d
d¼133.3 (d,
However, even if double bonds are also reduced, concerning
mechanistic consideration the formation of a radical species with
the indium system could be considered. The mechanism will be
further studied.
JCP¼9.2 Hz), 131.7 (d, JCP¼2.5 Hz), 129.0 (d, JCP¼10.5 Hz), 127.8 (d,
JCP¼55.9 Hz), 70.4 (d, JCP¼43.8 Hz), 62.1 (d, JCP¼8.6 Hz). 31P NMR
(121 MHz, CDCl3):
d¼16.5.
4.2.4. n-Propyldiphenylphosphine-borane [1013636-31-1] 2d. White
viscous oil. 1H NMR (300 MHz, CDCl3):
¼7.65e7.72 (m, 4H),
3. Conclusion
d
7.40e7.51 (m, 6H), 2.15e2.24 (m, 2H), 1.46e1.62 (m, 2H), 1.01 (t,
In conclusion we have developed an efficient method to reduce
phosphine oxides into their corresponding phosphines. The system
InBr3/TMDS has proven to be efficient to reduce aromatic and ali-
phatic phosphine oxides, to reduce tertiary and secondary phos-
phine oxides and finally to reduce phosphinic acids. This new
methodology can constitute an alternative to the current methods
to reduce phosphine oxides or recycle phosphine engaged in or-
ganic reactions.
J¼7.1 Hz, 3H). 13C NMR (75 MHz, CDCl3):
¼132.4 (d, JCP¼8.6 Hz),
d
131.3 (d, JCP¼2.5 Hz), 130.3, 129.1 (d, JCP¼9.9 Hz), 28.0 (d,
JCP¼36.4 Hz), 17.0, and 16.1 (d, JCP¼14.5 Hz). 31P NMR (121 MHz,
CDCl3):
d¼16.9.
4.2.5. 3-Methyl-1-phenylphospholane-borane [313478e78-3] 2e.
Colorless oil. 1H NMR (300 MHz, CDCl3):
¼7.64e7.71 (m, 2H),
d
7.39e7.41 (m, 3H), 1.92e2.30 (m, 5H), 1.50e1.64 (m, 2H), 1.13 (t,
J¼6.6 Hz, 3H). 13C NMR (75 MHz, CDCl3):
¼131.5 (d, JCP¼9.2 Hz),
d
4. Experimental part
4.1. General
131.3 (d, JCP¼2.5 Hz), 129.1 (d, JCP¼9.2 Hz), 38.7, 36.6, 28.4 (d,
JCP¼36.4 Hz), 27.2, and 21.4. 31P NMR (121 MHz, CDCl3):
¼31.6.
d
4.2.6. Diphenylcyclohexylphosphine borane [127686-90-2]
2f. White solid. 1H NMR (300 MHz, CDCl3):
¼7.70e7.77 (m, 4H),
7.41e7.48 (m, 6H), 2.33e2.46 (m, 1H), 1.56e1.85 (m, 5H), 1.40e1.53
(m, 2H), 1.23e1.30 (m, 3H). 13C NMR (75 MHz, CDCl3):
¼132.9 (d,
All reagentswereobtainedcommercially. Tetramethyldisiloxane,
97% (TMDS) was purchased from Aldrich, anhydrous Toluene from
Acros, indium bromide (III), 99.999% from Aldrich and the phos-
phine oxide derivatives from Aldrich and Alfa Aesar. All reagents and
reactants were used without further purification. All reactions were
performed under an inert atmosphere (argon) in a sealed tube. 1H
NMR, 13C NMR and proton coupled 31P NMR spectra were recorded
on a BRUKER DRX 300 or BRUKER ALS 300 and measurements are
given in parts per million. Chemical shifts are given in ppm.
d
d
JCP¼8.6 Hz), 131.2 (d, JCP¼2.4 Hz), 128.9 (d, JCP¼9.9 Hz), 33.9 (d,
JCP¼35.8 Hz), 26.0e30.0 (m, Cy). 31P NMR (121 MHz, CDCl3):
¼22.3.
d
4.2.7. 1,3-Bis(diphenylphosphino)propane [6737-42-4] 2g. White
viscous oil. 1H NMR (300 MHz, CDCl3):
d
¼7.34e7.40 (m, 8H),
7.26e7.28 (m, 12H), 2.20 (m, t, J¼7.7 Hz, 4H), 1.57e1.68 (m, 2H). 13C
NMR (75 MHz, CDCl3):
JCP¼18.5 Hz),128.7 (d, JCP¼11.7 Hz),128.67, 29.8 (t, JCP¼12.3 Hz), and
d
¼138.8 (d, JCP¼12.9 Hz), 132.9 (d,
4.2. General procedure for the preparation of compounds 2b
to 2f and 2i to 2l
27.2. 31P NMR (121 MHz, CDCl3):
d¼-16.2.
In a sealed tube containing a solution of the phosphine oxide
derivative (5 mmol) in anhydrous toluene (1 M) was added InBr3
(1 mol %, 0.05 mmol) and the TMDS (1.5 equiv, 7.5 mmol) under an
4.2.8. Tricyclohexylphosphineeborane [101965-91-7] 2i. White
solid. 1H NMR (300 MHz, CDCl3):
¼1.71e1.84 (m, 18H), 1.23e1.41
(m,15H). 13C NMR (75 MHz, CDCl3):
¼31.2 (d, JCP¼30.2 Hz), 28.2 (d,
d
d

L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155
3155
JCP¼1.8 Hz), 27.6 (d, JCP¼10.5 Hz) and 26.5. 31P NMR (121 MHz,
4. Appel, R. Angew. Chem. 1975, 87, 863e874; Green. Chem. 1975, 14, 801e811;
Buchanan, J. G.; Sable, H. Z. In; Thyagarajan, B. S., Ed. Selective Organic Trans-
formations; Wiley-Interscience: New York, 1972; vol. 2, pp 1e95.
5. Staudinger, H.; Meyer, J. Helv. Chim. Acta 1919, 2, 635e646.
6. Van Kalkeren, H. A.; Leenders, S. H. A. M.; Hommersom, C. R. A.; Rutjes, F. P. J. T.;
Van Delft, F. L. Chem.dEur. J. 2011, 17, 11290e11295.
7. (a) Imamoto, T.; Takeyama, T.; Kusumoto, T. Chem. Lett. 1985, 1491e1492; (b)
Busacca, C. A.; Raju, R.; Grinberg, N.; Haddad, N.; James-Jones, P.; Lee, H.; Lor-
enz, J. C.; Saha, A.; Senanayake, C. H. J. Org. Chem. 2008, 73, 1524e1531; (c)
Malpass, D. B.; Yeargin, G. S. U.S. patent 4,133,783, 1978; Bootle-Wilbraham, A.;
Head, S.; Longstaff, J.; Wyatt, P. Tetrahedron Lett. 1999, 40, 5267e5270; (d)
Cernia, E.; Giongo, G. M.; Marcati, F.; Marconi, W.; Palladino, N. Inorg. Chim. Acta
1974, 11, 195e200; (e) Griffin, S.; Heath, L.; Wyatt, P. Tetrahedron Lett. 1998, 39,
4405e4406.
CDCl3):
d
¼29.3.
4.2.9. Tri-n-butylphosphine-borane [4259-20-5] 2j. Colorless oil. 1H
NMR (300 MHz, CDCl3):
¼1.38e1.58 (m, 18H), 0.93 (t, J¼7.2 Hz,
d
9H). 13C NMR (75 MHz, CDCl3):
d
¼24.6 (d, JCP¼2.5 Hz), 24.2 (d,
JCP¼12.3 Hz), 22.8 (d, JCP¼34.5 Hz), and 13.5 (s). 31P NMR (121 MHz,
CDCl3):
d
¼15.6.
4.2.10. Tri-n-octylphosphine-borane [101965-92-8] 2k. Colorless oil.
1H NMR (300 MHz, CDCl3):
d
¼1.39e1.54 (m, 12H), 1.21e1.37 (m,
30H), 0.85 (t, J¼6.8 Hz, 9H). 13C NMR (75 MHz, CDCl3):
d
¼32.0, 29.3
¼15.6.
8. Handa, Y.; Inanaga, J.; Yamaguchi, M. J. Chem. Soc., Chem. Commun. 1989,
298e299.
9. Mathey, F.; Maillet, R. Tetrahedron Lett. 1980, 21, 2525e2526.
10. Hagemeyer, A.; Rieker, C. W.; Lautensack, T.; Hermeling, D. U.S. 5,689,005A,
1997.
(d, JCP¼3.7 Hz), 22.8 and 14.3. 31P NMR (121 MHz, CDCl3):
d
4.2.11. Diphenylphosphine-borane [41593-58-2] 2l. White solid. 1H
NMR (300 MHz, CDCl3):
¼7.50e7.57 (m, 4H), 7.27e7.37 (m, 6H).
11. Dockner, T. U.S. 4,727,193 A, 1988.
d
12. Fritzsche, H.; Hasserodt, U.; Van Olmen, J. U.S. 3,280,195, 1966.
13. (a) Petersson, M. J.; Loughlin, W. A.; Jenkins, I. D. Chem. Commun. 2008,
4493e4494; (b) Townsend, J. M.; Valentine, D. H. U.S. 4,008,282B, 1977.
14. Tanaka, H.; Yano, T.; Kobayashi, K.; Kamenoue, S.; Kuroboshi, M.; Kawakubo, H.
Synlett 2011, 582e584.
13C NMR (75 MHz, CDCl3):
d
¼133.1 (d, JCP¼9.2 Hz), 131.8 (d,
JCP¼2.5 Hz), 129.2 (d, JCP¼10.5 Hz), and 126.3 (d, JCP¼56.7 Hz). 31P
NMR (121 MHz, CDCl3):
d¼2.2 (d).
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Supplementary data
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