Highly regioselective silaboration of 3-substituted 1,2-dienes catalyzed by palladium/2,6-xylyl isocyanide

Article abstract of DOI:10.1055/s-1999-2917

Regioselective silaboration of 3-substituted 1,2-dienes was efficiently catalyzed by palladium/2,6-xylyl isocyanide complex, affording an adduct, in which the boryl and silyl groups were introduced at the central allenyl carbon and at the substituted alle

Full text of DOI:10.1055/s-1999-2917

LETTER
1567
Highly Regioselective Silaboration of 3-Substituted 1,2-Dienes Catalyzed by
Palladium/2,6-Xylyl Isocyanide
Michinori Suginome, Yutaka Ohmori, Yoshihiko Ito*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan
Fax +81 (75) 753-5668; E-mail: yoshi@sbchem.kyoto-u.ac.jp
Received 20 July 1999
2 mol %
Abstract: Regioselective silaboration of 3-substituted 1,2-dienes
was efficiently catalyzed by palladium/2,6-xylyl isocyanide com-
plex, affording an adduct, in which the boryl and silyl groups were
introduced at the central allenyl carbon and at the substituted allenyl
carbon, respectively.
O
O
R
Pd(acac)2
•
+
PhMe2Si
B
8 mol %
2,6-xylyl isocyanide
octane, 120 °C, 2 h
1a–f
2
Key words: silaboration, allenes, palladium/2,6-xylyl isocyanide,
regioselectivity, 2-boryl allylsilane
O
O
B
+
O
O
B
R
Regio- and stereoselective formation of metal–carbon
bonds is important in synthetic organic chemistry. In a se-
ries of papers,1 we have reported silicon–carbon bond for-
mation by bis-silylation reactions of carbon–carbon
multiple bonds with disilanes, which are efficiently cata-
lyzed by Pd(OAc)2 or Pd(acac)2 in the presence of tert-
alkyl isocyanide complex. In particular, it is remarked that
the palladium/tert-alkyl isocyanide complex is a most ef-
fective catalyst, which has made some intramolecular bis-
silylation reactions utilizable from organic synthesis
viewpoint.
PhMe2Si
R
SiMe2Ph
3a–f
3'a–f
Scheme 1
Based upon the bis-silylation reaction, recently we have
successfully developed a regioselective silaboration of
carbon–carbon multiple bonds.2–5 Of note is that a regio-
and stereoselective silaboration of terminal alkynes with
silylborane was also achieved most efficiently by use of
palladium/tert-alkyl isocyanide complex.2 However, ter-
minal alkenes were quite unreactive to the palladium cat-
alyzed silaboration. Instead, Pt(CH2=CH2)(PPh3)2
promoted the regioselective silaboration of terminal alk-
enes but in moderate yields.3
Herein, we wish to describe that the palladium/isocyanide
complexes catalyze the highly regioselective silaboration
of 3-substituted 1,2-dienes.6 Noteworthy is that palladium
catalyst complexed with 2,6-xylyl isocyanide rather than
tert-alkyl isocyanide provides the extremely high regiose-
lectivities for the silaboration.
The silaborations of some 3-substituted 1,2-dienes 1 with
(dimethylphenylsilyl)pinacolborane (2) were carried out
according to the following procedure. A solution of 5-
phenyl-1,2-pentadiene (1a; 1.5 mmol) and 2 (1.0 mmol)
in octane (0.5 mL) with palladium/2,6-xylyl isocyanide
complex generated in situ by mixing Pd(acac)2 (0.02
mmol) and 2,6-xylyl isocyanide (0.08 mmol) was heated
at 120 °C for 2 h under nitrogen atmosphere. The reaction
mixture was subjected to Kugelrohr distillation, giving 3a
in quantitative yield.7 Some results are summarized in Ta-
ble 1.
Symmetrical 1,3-disubstituted 1,2-diene 1g also under-
went the silaboration, giving the corresponding adducts as
a mixture of trans- and cis-isomers (62/38) in high yield.8
Synlett 1999, No. 10, 1567–1568 ISSN 0936-5214 © Thieme Stuttgart · New York

1568
M. Suginome et al.
LETTER
(4) Suginome, M.; Nakamura, H.; Matsuda, T.; Ito, Y. J. Am.
Chem. Soc. 1998, 120, 4248.
(5) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 1998,
17, 5233.
(6) Transition metal-catalyzed bismetalation reactions of 1,2-
dienes have been reported. For Si–Si, see: (a) Watanabe, H.;
Saito, M.; Sutou, N.; Nagai, Y. J. Chem. Soc., Chem.
Commun. 1981, 617. (b) Watanabe, H.; Saito, M.; Sutou, N.;
Kishimoto, K.; Inose, J.; Nagai, Y. J. Organomet. Chem.
1982, 225, 343. For Sn–Sn, see: (c) Killing, H.; Mitchell, T.
N. Organometallics 1984, 3, 1318. (d) Mitchell, T. N.;
Schneider, U. J. Organomet. Chem. 1991, 407, 319. For Si–
Sn, see: (e) Mitchell, T. N.; Killing, H.; Dicke, R.;
The silaboration of 3-substituted 1,2-dienes 1 was pro-
moted by palladium/1,1,3,3-tetramethylbutyl isocyanide
complex as well, providing 3 in high yield, which was,
however, accompanied by its regioisomer 3’, e.g., 1b (R =
Cy): 3b/3’b = 82/18 (90% total yield).9
A mechanism for the present regioselective silaborations
has not been elucidated. But, remarkable reverse of regio-
chemistry in the silaboration of 3-perfluorohexyl-1,2-pro-
padiene (1h) may suggest a significant electronic effect
for the regiochemical control (Scheme 2).10
Wickenkamp, R. J. Chem. Soc., Chem. Commun. 1985, 354.
For B–B, see: (f) Ishiyama, T.; Kitano, T.; Miyaura, N.
Tetrahedron Lett. 1998, 39, 2357.
(7) 3a: 1H NMR (CDCl3, 300 MHz) d 0.23 (s, 3H), 0.27 (s, 3H),
1.22 (s, 12H), 1.71-1.82 (m, 1H), 1.89-2.06 (m, 1H), 2.14 (dd,
J = 3.3, 12.0 Hz, 1H), 2.32-2.42 (m, 1H), 2.64-2.74 (m, 1H),
5.45 (d, J = 3.0 Hz, 1H), 5.92 (d, J = 3.0 Hz, 1H), 7.08-7.35
(m, 8H), 7.46-7.49 (m, 2H); 13C NMR (CDCl3, 75 MHz) d
–5.3, –3.9, 24.7, 30.9, 33.4, 35.2, 83.3, 125.5, 127.3, 127.5,
128.2, 128.6, 128.8, 134.3, 138.4, 143.1. Anal. Calcd for
C25H35BO2Si: C, 73.88; H, 8.68. Found: C, 73.71; H, 8.88.
(8) Selected analytical and spectroscopic data. The (E)-3g and
(Z)-3g were separated by HPLC and assigned to their
stereochemistry on the basis of NOE. (E)-3g: 1H NMR
(CDCl3, 300 MHz) d 0.22 (s, 3H), 0.27 (s, 3H), 0.78 (t, J = 7.2
Hz, 3H), 0.86 (t, J = 7.2 Hz, 3H), 1.01-1.21 (m, 2H), 1.21 (s,
12H), 1.23-1.45 (m, 4H), 1.97 (dd, J = 3.3, 11.7 Hz, 1H), 2.29
(q, J = 7.5 Hz, 2H), 5.75 (t, J = 7.8 Hz, 1H), 7.30-7.36 (m, 3H),
7.47-7.55 (m, 2H); 13C NMR (CDCl3, 75 MHz) d –4.9, –3.3,
13.6, 13.7, 21.9, 23.5, 24.7, 24.8, 31.6, 33.2, 33.7, 82.6, 127.4,
128.5, 134.3, 139.7, 144.0. (Z)-3g: 1H NMR (CDCl3, 300
MHz) d 0.20 (s, 3H), 0.34 (s, 3H), 0.77 (t, J = 6.9 Hz, 3H), 0.85
(t, J = 7.2 Hz, 3H), 0.90-1.08 (m, 1H), 1.20-1.40 (m, 4H), 1.21
(s, 6H), 1.22 (s, 6H), 1.72-2.09 (m, 3H), 2.22 (dd, J = 3.3, 12.0
Hz, 1H), 6.22 (t, J = 6.9 Hz, 1H), 7.30-7.36 (m, 3H), 7.48-7.57
(m, 2H); 13C NMR (CDCl3, 75 MHz) d –4.3, –3.3, 13.8, 14.1,
22.3, 22.9, 24.3, 24.9, 29.7, 30.7, 31.1, 82.6, 127.5, 128.5,
134.1, 140.1, 144.8.
Scheme 2
Finally, synthetic utility of 2-boryl allylsilane derivatives
thus prepared has been demonstrated by the palladium
catalyzed coupling reaction with aromatic halide (Scheme
3).11
CN
CN
3 mol % Pd(PPh3)4
+
3f
Ba(OH)2·8H2O
DME/H2O, reflux, 3 h
SiMe2Ph
I
4 (82%)
Scheme 3
(9) 3b: 1H NMR (CDCl3, 300 MHz) d 0.20 (s, 3H), 0.37 (s, 3H),
0.69-0.88 (m, 2H), 0.95-1.41 (m, 3H), 1.23 (s, 12H), 1.47-1.83
(m, 6H), 1.97 (d, J = 10.2 Hz, 1H), 5.43 (d, J = 3.3 Hz, 1H),
5.79 (d, J = 3.3 Hz, 1H), 7.25-7.40 (m, 3H), 7.45-7.60 (m, 2H);
13C NMR (CDCl3, 75 MHz) d –3.8, –1.3, 24.5, 24.7, 26.5,
26.6, 33.5, 34.2, 38.9, 41.5, 83.2, 127.4, 127.6, 128.3, 134.1,
140.9. 3’b: 1H NMR (CDCl3, 300 MHz) d 0.24 (s, 6H), 0.87-
1.07 (m, 2H), 1.07-1.36 (m, 2H), 1.19 (s, 12H), 1.56-1.72 (m,
6H), 1.78 (s, 2H), 2.60-2.73 (m, 1H), 5.63 (d, J = 9.3 Hz, 1H),
7.30-7.35 (m, 3H), 7.48-7.54 (m, 2H); 13C NMR (CDCl3, 75
MHz) d –3.3, 24.3, 24.8, 25.9, 26.0, 34.0, 39.4, 82.7, 127.5,
128.7, 133.9, 139.8, 151.7.
In summary, we have found new and regioselective sila-
boration of 3-substituted 1,2-dienes with (dimethylphe-
nylsilyl)pinacolborane, which was most efficiently cata-
lyzed by Pd(acac)2 (2 mol %) in the presence of 2,6-xylyl
isocyanide (8 mol %). The corresponding 2-boryl-3-silyl-
1-alkenes thus prepared may be utilizable as vinylborane
as well as allylsilane intermediates in organic synthesis.
References and Notes
(1) (a) Ito, Y.; Suginome, M.; Murakami, M. J. Org. Chem. 1991,
56, 1948. (b) Murakami, M.; Suginome, M.; Fujimoto, K.;
Nakamura, H.; Andersson, P. G.; Ito, Y. J. Am. Chem. Soc.
1993, 115, 6487. (c) Suginome, M.; Yamamoto, Y.; Fujii, K.;
Ito, Y. J. Am. Chem. Soc. 1995, 117, 9608. (d) Suginome, M.;
Matsumoto, A.; Ito, Y. J. Am. Chem. Soc. 1996, 118, 3061.
(e) Suginome, M.; Nakamura, H.; Ito, Y. Tetrahedron Lett.
1997, 38, 555. (f) Suginome, M.; Iwanami, T.; Ito, Y. J. Org.
Chem. 1998, 63, 6096. (g) Suginome, M.; Ito, Y. J. Chem.
Soc., Dalton Trans. 1998, 1925.
(10) 3’h: 1H NMR (CDCl3, 300 MHz) d 0.31 (s, 6H), 1.19 (s, 12H),
2.27 (t, J = 3.6 Hz, 2H), 6.03 (t, J = 16.5 Hz, 1H), 7.31-7.39
(m, 3H), 7.48-7.58 (m, 2H); 13C NMR (CDCl3, 75 MHz) d –
2.8, 21.7, 24.6, 84.4, 121.7, 122.0, 122.3, 127.7, 129.1, 133.8,
138.5. Anal. Calcd for C23H26BF13O2Si: C, 44.53; H, 4.23.
Found: C, 44.33; H, 4.12.
(11) 4: 1H NMR (CDCl3, 300 MHz) d 0.19 (s, 6H), 2.26 (s, 2H),
5.02 (s, 1H), 5.25 (s, 1H), 7.24-7.45 (m, 7H), 8.04-8.10 (m,
2H); 13C NMR (CDCl3, 75 MHz) d –3.3, 25.2, 114.3, 123.4,
127.0, 127.8, 129.2, 133.5, 137.9, 144.4, 146.8, 149.2.
(2) (a) Suginome, M.; Nakamura, H.; Ito, Y. Chem. Commun.
1996, 2777. (b) Suginome, M.; Matsuda, T.; Nakamura, H.;
Ito, Y. Tetrahedron 1999, 55, 8787.
(3) Suginome, M.; Nakamura, H.; Ito, Y. Angew. Chem. 1997,
109, 2627; Angew. Chem., Int. Ed. Engl. 1997, 36, 2516.
Article Identifier:
1437-2096,E;1999,0,10,1567,1568,ftx,en;Y15499ST.pdf
Synlett 1999, No. 10, 1567–1568 ISSN 0936-5214 © Thieme Stuttgart · New York