Chemistry Letters 2002
229
Table 2. Reduction Potentials and Products of Aromatic Active
a
transfer from Mg metal to appropriately activated aromatic ꢀ-
phosphorylacrylates, which might be of much use in organic
synthesis and material science.
Olefins
This research was supported by a Grant-in-Aid for Scientific
Research on Priority Areas (No. 13029038) from Ministry of
Education, Science, Sports and Culture, Japan.
References and Notes
1
D. R. M. Walton, ‘‘Organosilicon Compounds, Dictionary of
Organometallic Compounds,’’ Chapman and Hall, London
(
1984), Vol. 2.
2
3
E. W. Colvin, ‘‘Silicon Reagents in Organic Synthesis,’’
Academic Press, London (1988).
‘‘Organosilicon and Bioorganosilicon Chemistry –Structure,
Bonding, Reactivity, and Synthetic Application,’’ ed. by H.
Sakurai, Ellis Horwood, Chichester (1985).
4
5
6
T. Ohno, H. Nakahiro, K. Sanemitsu, T. Hirashima, and I.
Nishiguchi, Tetrahedron Lett., 33, 5515 (1992).
J.-P. Picard, A. Ekouya, J. Dunogues, N. Duffaut, and R.
Calas, J. Organomet. Chem., 93, 51 (1975).
I. Nishiguchi, Y. Kita, Y. Ishino, H. Maekawa, Y. Yamazaki,
and T. Ohno, 43rd Symposium on Organometallic Chemistry
of Kinki Chemical Society, Osaka, 1996; Abstr., No. B212.
Calas et al. represented the used solvent, hexamethylpho-
sphortriamide ((Me2N)3PO) as the abbreviation HMPT in
their series of Mg-promoted reactions. However, the solvent,
7
(
Me2N)3PO, is represented as carcinogenic hexamethylpho-
ꢁ
-silylated product 6A (9% yield) were obtained accompanying
sphoric triamide (HMPA) and should be different from
hexamethylphosphorous triamide ((Me N) P) (HMPT)
which may be too reactive to use as a solvent.
with formation of much tarry material, as shown in Table 2.
Cyclic voltammetry of these aromatic ꢀ-phosphorylacrylates
2
3
8
1
a, 1e, 1h, 3 and the related compounds 4-6 may provide some
8
9
J.-P. Picard, J. Organometal. Chem., 34, 279 (1972).
S. Yamazaki, T. Takada, T. Imanishi, Y. Moriguchi, and S.
Yamabe, J. Org. Chem., 63, 5919 (1998).
significant informations for elucidation of remarkable differences
in their reaction behaviors, as shown in Table 2. There seems a
tendency in the present reactions that the reaction of a substrate
possessing more negative reduction potential gives a hydro-
dimerzation product (type C) while a simply hydrogenated
product (type B) is obtained to some extent from that of a substrate
possessing a less negative reduction potential. A substrate such as
10 C. N. Robinson and C. D. Slater, J. Org. Chem., 52, 2011
(1987).
11 M. T. Reetz, R. Peter, and M. V. Itzstein, Chem. Ber., 120, 121
(1987).
12 All the products 2a-h, 3A, 3C, 4A-C, 5A-B, 6A-B, and 7A-B
1
13
ꢀ
-phosphorylacrylates 1a-h, whose reduction potential are
were characterized by spectroscopic methods ( H- and C-
NMR, IR, Mass), and elementary analysis.
À1:70-À1:80 V, are most suitable for the present Mg-promoted
regioselective C-silylation, giving a type A product predomi-
nantly.
13 T. Hirao, T. Masunaga, N. Yamada, Y. Ohshiro, and T.
Agawa, Bull. Chem. Soc. Jpn., 55, 909 (1982).
The present Mg-promoted reductive silylation may proceed
through electron transfer from Mg metal to activated electron–
difficient olefins 1a-h to give the corresponding radical anions,
which are successively subjected to electrophlic attack of TMSCl,
second electron transfer and protonation. Different reaction
behaviors of a variety of activated olefins, depending upon their
reduction potentials, may be attributed to stability and reactivity
of the corresponding radical anions.
As a conclusion, efficient and facile regioselective formation
of C-Si bond was successfully accomplished through electron
14 Use of 0.5eq of TMSCl in the reaction of 3 resulted in some
increase in the yield of the hydrodimerization product 3C to
39%, and formation of a trace amount of the silylated product
3A.
15It may be one of plausible explanation that a less stable radical
anion from 3 is apt to dimerize at a proximity to Mg metal
surface while a more stable one form 4-6 has enough life-time
to diffuse into a bulk solution and to catch a proton rather than
reactive TMSCl.
15