ORGANIC
LETTERS
2002
Vol. 4, No. 4
667-669
Conjugate Addition of Organosiloxanes
to r,â-Unsaturated Carbonyl
Compounds Catalyzed by a Cationic
Rhodium Complex
Shuichi Oi,* Yoshio Honma, and Yoshio Inoue
Department of Materials Chemistry, Graduate School of Engineering,
Tohoku UniVersity, Sendai 980-8579, Japan
Received January 7, 2002
ABSTRACT
A novel, additive-free, and clean conjugate addition reaction of organosiloxanes to r,â-unsaturated carbonyl compounds catalyzed by a
cationic rhodium complex in water-containing solvent has been developed. A plausible reaction mechanism involving the additive-free
transmetalation step between the rhodium complex and the silicon reagent is proposed.
Transition metal-catalyzed transformations using organome-
tallic reagents are of great importance in modern organic
chemistry.1 Especially, organotin and organoboron reagents
are recognized to be very useful in that these reagents are
readily available, stable to air and moisture, and tolerate a
variety of functional groups on either reaction partner. We
previously reported the rhodium-catalyzed addition of aryl-
stannanes to aldehydes and aldimines2 and the conjugate
addition of arylstannanes to R,â-unsaturated carbonyl com-
pounds.3 Miyaura reported the addition of organoboronic
acids to aldehydes and aldimines4 and to R,â-unsaturated
carbonyl compounds5 catalyzed by rhodium complexes. In
these addition reactions, organorhodium complexes generated
by transmetalation with the organotin or organoboron
compounds are assumed to be the active species which react
with the substrates. As an advantageous feature of these
addition reactions, it was reported recently that the reactions
can be performed in air and water.6,7
Organosilicon reagents are more attractive from the
viewpoint stated above. However, the organosilicon reagents
are less reactive than those of tin and boron and, therefore,
need to be activated somehow. Fluoride ion is generally
known to be a good activating reagent for organosilicon
reagents, which generates reactive five-coordinate silicates.
The palladium-catalyzed cross-coupling reaction of organo-
silicon reagents with organic halides in the presence of
fluoride ion was developed by Tamao and Hiyama,8 and
some related practical coupling reactions, involving the use
of the activator other than fluoride ion, were reported.9
Recently, we developed the addition of arylfluorosilanes
to aldehydes catalyzed by a rhodium complex in the presence
(1) Knight, D. W. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 3, pp 481-520.
(2) (a) Oi, S.; Moro, M.; Inoue, Y. Chem. Commun. 1997, 1621. (b) Oi,
S.; Moro, M.; Fukuhara, H.; Kawanishi, T.; Inoue, Y. Tetrahedron Lett.
1999, 40, 9259.
(3) (a) Oi, S.; Moro, M.; Ono, S.; Inoue, Y. Chem. Lett. 1998, 83. (b)
Oi, S.; Moro, M.; Ito, H.; Honma, Y.; Miyano, S.; Inoue, Y. Tetrahedron
2002, 58, 91.
(4) (a) Sakai, M.; Ueda, M.; Miyaura, N. Angew. Chem., Int. Ed. 1998,
37, 3279. (b) Ueda, M.; Miyaura, N. J. Org. Chem. 2000, 65, 4450. (c)
Ueda, M.; Saito, A.; Miyaura, N. Synlett 2000, 1637.
(5) (a) Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics 1997, 16,
4229. (b) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N.
J. Am. Chem. Soc. 1998, 120, 5579. (c) Sakuma, S.; Sakai, M.; Itooka, R.;
Miyaura, N. J. Org. Chem. 2000, 65, 5951.
(6) (a) Meng, Y.; Li, C. J. J. Am. Chem. Soc. 2000, 120, 9538. (b)
Venkatraman, S.; Li, C. J. Tetrahedron Lett. 2001, 42, 781.
(7) Itooka, R.; Iguchi, Y.; Miyaura, N. Chem. Lett. 2001, 722.
(8) (a) Tamao, K.; Kobayashi, K.; Ito, Y. Tetrahedron Lett. 1989, 30,
6051. (b) Hatanaka, Y.; Fukushima, S.; Hiyama, T. Chem. Lett. 1989, 1711.
(c) Hiyama, T.; Hatanaka, Y. Pure Appl. Chem. 1994, 66, 1471.
10.1021/ol025518h CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/22/2002