6458
J . Org. Chem. 1997, 62, 6458-6459
Ta ble 1. Rea ction of 1-Iod on a p h th a len e u n d er Va r iou s
Con d ition sa
Novel P a lla d iu m (0)-Ca ta lyzed Cou p lin g
Rea ction of Dia lk oxybor a n e w ith Ar yl
Ha lid es: Con ven ien t Syn th etic Rou te to
Ar ylbor on a tes
yield (%)b
entry
catalyst
base
none
Et3N
i-Pr2NEt dioxane
pyridine dioxane
DBU
KOAc
Et3N
solvent
dioxane
dioxane
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
PdCl2(dppf)c
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(PPh3)2
PdCl2(PPh3)2/PPh3 Et3N
Pd(PPh3)4
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
0
3
89
64
12
3
6
75
0
6
29
47
36
82
13
0
1
7
7
8
Miki Murata, Shinji Watanabe, and
Yuzuru Masuda*
Department of Materials Science, Kitami Institute of
Technology, Kitami 090, J apan
dioxane
dioxane
dioxane
dioxane
dioxane
toluene
CH2ClCH2Cl 81
CH3CN
DMF
Received J une 2, 1997
Et3N
Et3N
Et3N
Et3N
Et3N
10
79
Arylboronic acids and their esters are valuable re-
agents in organic synthesis,1,2 and much attention has
been paid to them in the study of molecular recognition.3
Arylboron compounds can be prepared by the transmeta-
lation between arylmagnesium or -lithium reagents and
boron compounds having good leaving groups, such as
halogen and alkoxy groups,4 and then in a few cases this
synthesis has been accomplished using boranes that
contain a boron-hydrogen bond.5
Recently, Miyaura and co-workers reported on a pal-
ladium-catalyzed coupling reaction of tetraalkoxydiboron,
which provided a one-step procedure for deriving aryl-
boronates from aryl halides.6 Kunai and his colleague
have found that the PdCl2-catalyzed reaction of alkyl
iodides with Et2SiH2 afforded Et2ISi-R to some extent,7
indicating the potential use of metal hydrides as a
metalating reagent in the presence of palladium catalyst.
To our knowledge, however, there has been no report of
a catalytic reaction using hydroboranes as a boron source
other than for hydroboration.8 We here describe a novel
palladium-catalyzed coupling reaction of dialkoxyhy-
droborane 2 with aryl halides 1 in the presence of a base
and affording the corresponding arylboronates 3 (eq 1).
Since pinacolborane 2 tolerates various functional groups
83
27
23
a
Reactions of 1-iodonaphthalene 1 (1.0 mmol) with 2 (1.5 mmol)
were carried out at 80 °C for 2 h in 4 mL of solvent by using 3 mol
b
% of catalyst and base (3 mmol). GLC yields are based on 1 used.
c dppf is 1,1′-bis(diphenylphosphino)ferrocene.
and the expecting pinacolboronates 3 are insensitive to
air and moisture,9 the coupling reaction should allow for
a wide range of 3.
The results of the reaction using 1-iodonaphthalene as
1 with 1.5 equiv of 2 under various conditions are
summarized in Table 1. This coupling was achieved with
the aid of palladium catalysts and bases in analogy with
the Suzuki-Miyaura cross-coupling reaction (entry 1 and
2).1c The products were contaminated with naphthalene
4, the normal cross-coupling product, in each case as a
result of the behavior of pinacolborane as a hydride.
However, this situation was prevented by the choice of a
suitable base. Thus, the tertiary amine, especially Et3N,
was recognized to be most effective for the selective
formation of 3 (entry 2 and 3).10 In the presence of other
weak bases, which were generally known not to contrib-
ute to the transmetalation of boron compounds, the
formation of undesirable 4 unexpectedly predominated
(entries 4-6). The reaction was efficiently catalyzed by
the palladium(II) complexes having 2 equiv of phosphine
ligands (entry 2 and 7). An additional phosphine ligand
tended to retard the reaction (entry 8 and 9). In testing
the four solvents, dioxane, toluene, MeCN, and
CH2ClCH2Cl, it was found that these did not play an
important role in the present reaction (entries 2 and 10-
12). However, the use of polar solvent, DMF, caused low
yield and low selectivity due to decomposition of dialkoxy-
borane to diborane (entry 13).11
(1) For the cross-coupling reaction of arylboronates, see: (a) Wa-
tanabe, T.; Miyaura, N.; Suzuki, A. Synlett 1992, 207. (b) Saito, S.;
Sakai, M.; Miyaura, N. Tetrahedron Lett. 1996, 37, 2993. (c) For a
recent review, see: Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(2) For an efficient Lewis acid catalyst, see: (a) Ishihara, K.;
Kurihara, H.; Yamamoto, H. J . Am. Chem. Soc. 1996, 118, 3049. (b)
Ishihara, K.; Maruyama, T.; Mouri, M.; Gao, Q.; Furuta, K.; Yamamoto,
H. Bull. Chem. Soc. J pn. 1993, 66, 3483. (c) Ishihara, K.; Mouri, M.;
Gao, Q.; Maruyama, T.; Furuta, K.; Yamamoto, H. J . Am. Chem. Soc.
1993, 115, 11490.
(3) For a review for the recognition of saccharide, see: J ames, T.
D.; Linnane, P.; Shinkai, S. Chem. Commun. 1996, 281.
(4) (a) Onak, T. Organoborane Chemistry; Academic: New York,
1975. (b) Brown, H. C. Organic Syntheses via Boranes; Wiley: New
York, 1975.
(5) (a) Breuer, S. W.; Thorpe, F. G.; Podesta´, J . C. Tetrahedron Lett.
1974, 3719 and references cited therein. (b) Brown, H. C.; Rogic, M.
M. J . Am. Chem. Soc. 1969, 91, 4304.
(6) Ishiyama, T.; Murata, M.; Miyaura, N. J . Org. Chem. 1995, 60,
7508.
(7) Kunai, A.; Sakurai, T.; Toyoda, E.; Ishikawa, M.; Yamamoto, Y.
Organometallics 1994, 13, 3233.
(8) (a) Ma¨nnig, D.; No¨th, H. Angew. Chem., Int. Ed. Engl. 1985, 24,
878. (b) For a recent review, see: Burgess, K.; Ohlmeyer, M. J . Chem.
Rev. 1991, 91, 1179.
(9) (a) Tucker, C. E.; Davidson, J .; Knochel, P. J . Org. Chem. 1992,
57, 3482. (b) Pereira, S.; Srebnik, M. Tetrahedron Lett. 1996, 37, 3283
and references cited therein.
(10) The abnormal cross-coupling reaction of 1-alkenylboronates
with aryl iodide in the presence of Et3N has been reported. See:
Miyaura, N.; Yamada, K.; Suginome, H.; Suzuki, A. J . Am. Chem. Soc.
1985, 107, 972.
(11) Garrett, C. E.; Fu, G. C. J . Org. Chem. 1996, 61, 3224.
(12) A representative procedure is as follows. A flask was charged
with PdCl2(dppf) (0.03 mmol), dioxane (4 mL), aryl iodide 1 (1.0 mmol),
Et3N (3.0 mmol), and pinacolborane 2 (1.5 mmol) under an argon flow,
and the mixture was stirred at 80 °C. GLC analysis showed the
completion of the reaction. The reaction mixture was diluted with
benzene, washed with water, and dried over MgSO4. The solvent was
evaporated, and product 3 was isolated by Kugelrohr distillation.
The results obtained with representative aryl iodides
or bromides 1, giving the corresponding products 3
similarly as above, are listed in Table 2.12 The differences
in the yields and the selectivity among aryl iodides
having electron-donating or -withdrawing groups were
not particularly large (entries 1-9). Above all, the
presence of functional groups, such as CO2Et (entry 6),
COMe (entry 7), and CN (entry 8), in the starting 1 did
not interfere with the outcome of the present reaction at
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