The present work was supported in part by a Grant-in-Aid for
Scientific Research on Priority Areas No. 283, ‘Innovative
Synthetic Reactions’ from Monbusho. Y. M. gratefully ac-
knowleges the financial support of this research by the Japan
Society for the Promotion of Science in the form of Research
Fellowships for Young Scientists.
R2 Yb R2
R1
H
R1
N
+
2
Yb
C
N
THF/HMPA
R2
CH HC
R1
R1
1
A
R3
H
C
Notes and References
O
R2 Yb R2
R1
N
Yb
NR2
† E-mail: yfujitcf@mbox.nc.kyushu-u.ac.jp
R2N
H
R1
2 R3CHO
‡ Typical procedure for the dehydrogenative coupling of 1 with Yb metal:
THF (2 ml), HMPA (0.5 ml) and methyl iodide (2 ml) were successively
added to a mixture of 1c (211 mg, 1.0 mmol) and ytterbium (87 mg, 0.5
mmol) under argon, which was stirred for 2 h at room temperature. Then,
1-NpCHO (156 mg, 1.0 mmol) was added to the mixture. The resulting
mixture was stirred for an additional 2 h at room temperature. Usual work-
up followed by a silica gel column chromatography (n-hexane–ethyl
acetate) gave 119 mg (57%) of the desired compound 2c.
O
CH CH
C
R1
R1
H
R1
H
R3
B
OCH2R3
Yb
NR2
R2N
1 T. Imamoto, Lanthanides in Organic Synthesis, Academic Press,
London, 1994, pp. 7–19; Y. Fujiwara, K. Takaki and Y. Taniguchi,
J. Alloys Compd., 1993, 192, 200.
R1
NR2
+
Yb(OCH2R3)2
R1
O
R1
NR2
C
R1
H
2 For example, Z. Hou, K. Takamine, K. Aoki, O. Shiraishi, Y. Fujiwara
and H. Taniguchi, J. Org. Chem., 1988, 53, 6077; Z. Hou, H. Yamazaki,
K. Kobayashi, Y. Fujiwara and H. Taniguchi, J. Chem. Soc., Chem.
Commun., 1992, 722; K. Takaki, F. Beppu, S. Tanaka, Y. Tsubaki, T.
Jintoku and Y. Fujiwara, J. Chem. Soc., Chem. Commun., 1990, 516; Y.
Makioka, S. Uebori, M. Tsuno, Y. Taniguchi, K. Takaki and Y. Fujiwara,
Chem. Lett., 1994, 611; Y. Makioka, M. Tsuno, S. Ueboki, Y. Taniguchi,
K. Takaki and Y. Fujiwara, J. Org. Chem., 1996, 61, 372.
3 K. Takaki, Y. Tsubaki, S. Tanaka, F. Beppu and Y. Fujiwara, Chem. Lett.,
1990, 203; K. Takaki, S. Tanaka and Y. Fujiwara, Chem. Lett., 1991, 493;
Y. Taniguchi, T. Kuno, M. Nakahashi, K. Takaki and Y. Fujiwara,
J. Alloys Compd., 1994, 216, L9-12; Y. Taniguchi, T. Kuno, M.
Nakahashi, K. Takaki and Y. Fujiwara, Appl. Organomet. Chem., 1995,
9, 491.
4 T. Imamoto and S. Nishimura, Chem. Lett., 1990, 1141; E. J. Enholm,
D. C. Forbes and D. P. Holub, Synth. Commum., 1990, 20, 981; A.
Lebrun, E. Rantze, J.-L. Namy and H. B. Kagan, New J. Chem., 1995, 19,
699.
5 Y. Makioka, Y. Taniguchi, Y. Fujiwara, K. Takaki, Z. Hou and Y.
Wakatsuki, Organometallics, 1996, 15, 5476.
H
R3
2
Scheme 1
Although the reaction mechanism is not yet clear, a possible
reaction mechanism is shown in Scheme 1. First, one atom of
ytterbium metal reacts with two molecules of aldimine 1 via
two-electron transfer from ytterbium to give a diazametalla-
cyclopentane intermediate B, probably via formation of an
intermediate A.6 Subsequent treatment with an aldehyde would
cause the coordination and double hydrogen transfer, as in a
similar manner to the Meerwin–Pondorf–Varley reduction/
Oppenauer oxidation,7 to give 2 and ytterbium alkoxides, which
gives an alcohol R3CH2OH after hydrolysis.
In summary, ethane-1,2-diimines 2 can be prepared from the
reaction of aromatic aldimines 1 with ytterbium metal followed
by treatment with aromatic aldehydes. To the best of our
knowledge, this is the first example of metal mediated
dehydrogenative coupling of aldimines. Further mechanistic
investigation and extension of this reaction are in progress.
6 J. G. Smith and I. Ho, J. Org. Chem., 1972, 37, 653.
7 C. Djerassi, Org. React., 1951, 6, 207.
Received in Cambridge, UK, 23rd February 1998; 8/01514G
1102
Chem. Commun., 1998