A novel transmetallation of triarylstibanes into arylboronate: Boro-induced ipso-deantimonation and its theoretical calculation

Article abstract of DOI:10.1246/cl.2006.1402

Treatment of triarylstibanes with boron trichloride followed by derivatization with methanol and 1,3-propanediol afforded arylboronates in good yield with all three aryl groups on the antimony being utilized. Theoretical calculation of the reaction pathwa

Full text of DOI:10.1246/cl.2006.1402

1402
Chemistry Letters Vol.35, No.12 (2006)
A Novel Transmetallation of Triarylstibanes into Arylboronate:
Boro-induced Ipso-deantimonation and Its Theoretical Calculation
Shuji Yasuike,1;2 Kazuhide Nakata,3 Weiwei Qin,1
Toshiyuki Kaji,2 and Jyoji Kuritaꢀ1
1Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi, Kanazawa 920-1181
2Organization for Frontier Research in Preventive Pharmaceutical Sciences, Hokuriku University,
Kanagawa-machi, Kanazawa 920-1181
3Science Research Center, Hosei University, 2-17-1 Fujimi, Chiyoda-ku, Tokyo 102-8160
(Received August 1, 2006; CL-060876; E-mail: j-kurita@hokuriku-u.ac.jp)
a
Table 1. Reaction of Ph3M (M = P, As, Sb, and Bi) with BCl3
Treatment of triarylstibanes with boron trichloride followed
by derivatization with methanol and 1,3-propanediol afforded
arylboronates in good yield with all three aryl groups on the
antimony being utilized. Theoretical calculation of the reaction
pathway revealed that the transformation proceeds through
boro-induced ipso-deantimonation and the reactivity of Ph3M
(M = P, As, Sb, and Bi) should be governed by the stability
of the corresponding cations Ar2Mþ.
O
B
O
7a
1) BCl3
Me
Me
Ph3M
3
Ph
2) MeOH
3) 2,2-Dimethyl-1,3-propanediol
1
4
Me
Me
OMe
HO
HO
BCl3
Cl
Cl
MeOH
Ph
B
3
Ph
B
3
OMe
5
6
The utility of arylboronic acids and their esters in organic
synthesis has attracted much attention in recent years, particular-
ly through developments in the Suzuki–Miyaura coupling
reaction.1,2 Several approaches for the synthesis of arylboron
derivatives have been reported.2–4 Among these, it is known that
the propensity of arylsilanes5 and -stannanes6 to undergo ipso-
substitution allows smooth transmetallation from silicon and
tin to boron by treatment with boron halides (BX3), leading to
ArBX2. However, the transmetallation of organo-pnictogen
(group 15 element: P, As, Sb, and Bi) compounds into arylboron
compounds has not been reported so far. Herein, we describe the
first approach of the metal exchange reaction from group 15
element to boron. In the present studies, treatment of triarylsti-
banes (Ar3Sb) with boron trichloride (BCl3) followed by deriva-
tization with methanol and 2,2-dimethyl-1,3-propanediol afford-
ed boronates in good yield with all three aryl groups on the
antimony being utilized.
We first examined the reaction of triphenylpnictogens 1–4
with BCl3 (3.6 equiv.), followed by quenching with methanol
and derivatization with 2,2-dimethyl-1,3-propanediol. The re-
sults including reaction conditions are summarized in Table 1.
Triphenylstibane 3a (M = Sb) was effectively converted to
phenylboronate 7a, though 1 (M = P) and 2 (M = As) showed
no ability to transform (Entries 1–3). It should be noted that all
three phenyl groups on the antimony participated in the reaction
of 3a with BCl3. On the other hand, the reaction of 4 (M = Bi)
Yield/%c
Conditions
ꢁC/h
Entry
M
7a
Ph3M:Recovery
1
2
3
4b
5b
P (1)
0/2
0/2
0/2
0/2
0
0
88
35
44
97
98
0
0
0
As (2)
Sb (3a)
Bi (4)
Bi (4)
ꢂ78/4
aAll reactions were carried out using Ph3M (1 mmol), BCl3 (3.6
mmol), MeOH (3 mL), and 2,2-dimethyl-1,3-propanediol (10
.
mmol). There was a by-product [Ph2B–O–BPh2 H2O (Entry 4;
b
c
54%, Entry 5; 16%)]. Isolated yield.
These results revealed that the three phenyl groups on the
antimony in 3a reacted with BCl3 one by one via Ph2SbCl
and PhSbCl2.
In order to evaluate the generality and applicability of this
transmetallation, we attempted a reaction between BCl3 and a
variety of triarylstibanes, and the results are summarized in
Table 2. Triarylstibanes 3b–3g were treated under the standard
conditions employed for entry 3 in Table 1. In all cases, the
corresponding arylboronates 7b–7g were formed in good yield
Table 2. Boro-induced ipso-deantimonationa
O
1) BCl3
Me
Me
Ar3Sb
Ar
B
3
2) MeOH
O
3) 2,2-Dimethyl-1,3-propanediol
3b 3g
7b 7g
.
with BCl3 gave a side product Ph2B–O–BPh2 H2O, which might
result from the reaction of Ph2BCl with water during work-up of
the reaction mixture. This result indicates that the Ph–Bi bond in
4 would be more reactive than the Ph–Sb bond in 3a, and PhBCl2
initially formed can react with the phenylbismuthane derivatives
to form Ph2BCl (Entries 4 and 5). Thus, only 3a was converted to
dichloroborane intermediate 5, which was transformed to 7a via
6 by successive treatment with methanol and 1,3-propanediol.7
Also apparent was that treatment of Ph2SbCl and PhSbCl2 with
BCl3 (2.4 and 1.2 equiv., 0 ꢁC/2 h) resulted in similar trans-
metallation to afford 7a in 61 and 54% yields, respectively.
Entry
Substrate
Ar
Yield/%b
1
2
3
4
5
6
3b
3c
3d
3e
3f
4-Methoxyphenyl
4-Methylphenyl
4-Fluorophenyl
4-Chlorophenyl
2-Methylphenyl
1-Naphthyl
57 (7b)
85 (7c)
83 (7d)
92 (7e)
68 (7f)
80 (7g)
3g
aAll reactions were carried out using Ar3Sb (1 mmol), BCl3 (3.6
mmol), MeOH (3 mL), and 2,2-dimethyl-1,3-propanediol
b
(10 mmol). Isolated yield.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.12 (2006)
1403
ipso-deantimonation and its divisional theoretical calculation
of the reaction pathway was made. Synthetic application and
work on the detailed reaction mechanism are in progress.
δ
Cl
Cl3B MPh2
Cl2B
BCl3
BCl3
MPh2
MPh2
H
MPh2
H
δ
8
10
9a
9b
This work was supported by a Grant-in-Aid for Scientific
Research (C) from the Ministry of Education, Culture, Sports,
Sciences and Technology of Japan (to J. K.); the ‘‘Academic
Frontier’’ Project for Private Universities from the Ministry
Education, Culture, Sports, Sciences and Technology of Japan
(to S. Y. and T. K.); and the Specific Research Fund of Hokuriku
University, which is gratefully acknowledged.
(28.7)
(8.3)
(27.6)
(28.3)
(27.5)
(24.2)
(24.1)
(23.1)
M=P
(21.8)
(7.9)
(19.4)
M=As
(15.5)
(3.6)
5
(16.1)
+
8
M=Sb
M=Bi
Cl-MPh2
(0)
References and Notes
(-4.9)
1-4
+
BCl3
(-7.6)
(-9.0)
1
2
3
a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457. b) S. Kotha,
K. Lahiri, D. Kashinath, Tetrahedron 2002, 58, 9633.
10
9
(-16.6)
A. Suzuki, H. C. Brown, Organic Syntheses via Boranes, Aldrich
Chemical Company, Inc., Milwaukee, Wisconsin, 2003, Vol. 3.
a) D. S. Matteson, The Chemistry of the Metal–Carbon Bond, ed. by
F. R. Hartley, S. Patai, Wiley, New York, 1987, Vol. 4, p. 307. b) N.
Miyaura, K. Maruoka, Synthesis of Organometallic Compounds, ed.
by S. Kojima, Wiley, New York, 1997, p. 345.
(-28.2)
(-36.7)
Reaction coordinate
ˇ
ˇ
4
5
a) P.-E. Broutin, I. Cerna, M. Campaniello, F. Leroux, F. Colobert,
Org. Lett. 2004, 6, 4419. b) M. Murata, T. Oyama, S. Watanabe, Y.
Masuda, J. Org. Chem. 2000, 65, 164, and reference cited therein.
For recent examples, see: a) Z. Zhao, V. Snieckus, Org. Lett. 2005,
7, 2523. b) E. Hupe, M. I. Calaza, P. Knochel, Chem. Commun.
Figure 1. Calculated reaction coordinates for 1–4 to give 5.
Numbers in parentheses are relative energies against reactants.
with all three aryl groups on the antimony being used.8 Also
apparent was that the position of the substituent on the aryl group
was retained during the reaction. These results imply that the re-
action took place through boro-induced ipso-deantimonation,
which will be the first example of the ipso-attack against organo-
stibanes by boron halide.
2002, 1390. c) M. Pottlander, N. Palmer, P. Knochel, Synlett
1996, 573.
For recent examples, see: a) G. J. P. Britovsek, J. Ugolotti, A. J. P.
¨
6
White, Organometallics 2005, 24, 1685. b) M. Schulte, F. P. Gabbaı,
¨
Can. J. Chem. 2002, 80, 1308. c) B. Schilling, V. Kaiser, D. E.
Kaufmann, Chem. Ber. 1997, 130, 923.
M. Lauer, H. Bohnke, R. Grotstollen, M. Salehnia, G. Wulff, Chem.
¨
Ber. 1985, 118, 246.
7
8
We next examined a theoretical calculation (RHF/Lan
L2DZ level) to reveal the difference in the reactivity toward
the above transmetallation (Figure 1).9 The reaction initially
proceeds from an electrophilic attack of BCl3 on the ipso-posi-
tion of 1–4 to form transition state 8 whose structure is similar
to those of Wheland complexes. The transformation of Ph3M
into 8 may be the rate-determining step for all substrates; activa-
tion energies are 16.1 kcal molꢂ1 for M = Bi, 19.4 kcal molꢂ1
for M = Sb, and 24.2 kcal molꢂ1 for M = As. Then, the Ph2M
moiety rearranges on the ortho-position to give intermediate 9
which can be described as a resonance hybrid between 9a and
9b. In the second step, one of the chloride ions moved rapidly
toward M to give the product 5 and Ph2MCl. Structures of the
transition states 10 are similar to those of 9. A similar pathway
for 1 (M = P) was also found at the same theoretical level,
though the Wheland complex 8 was obtained as an intermediate
accompanied by two transition states in front and behind. The
Ph2P moiety in 9b moved on other ortho-position in order to
change the conformation of the phenyl rings, which make the
chloride transfer feasible. Calculated activation energy of this
reaction was 28.7 kcal molꢂ1. All these proposed mechanisms
are supported by the experimental results such as the ipso-attack
and the order of reactivity. It has become apparent that the reac-
tivity of this type of reaction is governed by the stability of the
intermediate 9, or, more essentially, by the stability of the cation
Ar2Mþ. These results imply that information concerning the
stability of the cations provides guidelines for the synthesis of
various arylboronates.
All reactions were carried out under argon using standard Schlenk
techniques. Boron trichloride (1.0 M solution in dichloromethane,
3.6 mL, 3.6 mmol, 3.6 equiv.) was added to a stirred solution of
triarylstibane 3a–3g (1.0 mmol) in dichloromethane (1 mL) at
0 ꢁC. The mixture was stirred for 2 h at the same temperature, and
then allowed to warm at room temperature. The solvent was re-
moved under reduced pressure and the residual oil was dissolved
in methanol (3 mL). After stirring the mixture for 30 min at room
temperature, 2,2-dimethyl-1,3-propanediol (1.06 g, 10 mmol) was
added and stirring was continued for 1 h. The solvent was removed
under reduced pressure and the crude product was purified by
silica-gel column chromatography using hexane/CH2Cl2 as eluents.
7a: 501 mg, mp 62–64.5 ꢁC, 7b: 376 mg, mp 54–56 ꢁC, 7c: 520 mg,
mp 92–95 ꢁC, 7d: 517 mg, mp 65–67 ꢁC, 7e: 618 mg, mp 97–99 ꢁC,
7f: 416 mg, oil, 7g: 576 mg, mp 68–70 ꢁC.
All calculations were performed at the RHF/LanL2DZ level with
Gaussian 03 program: M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery,
Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
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J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
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9
In conclusion, we have disclosed a novel transmetallation
of triarylstibanes into arylboronates based on boro-induced
Published on the web (Advance View) November 11, 2006; doi:10.1246/cl.2006.1402