Scheme 2
of aryl iodides using commercially available diethylzinc. The 1,4-
addition and allylation reaction of the arylzinc prepared in this
manner proceeded smoothly under copper-free conditions and the
promotor is also considered to enhance the reactivity of arylzinc
compounds toward electrophiles. Further investigations on the
scope and limitation of the t-Bu-P4 base-promoted reaction of
organozinc compounds and the mechanistic studies on this
activation are underway.
This work was partly supported by the Grant-in Aid for
Scientific Research (No. 16659002, No. 16033208, No. 16390002)
from the Ministry of Education, Science, Sports and Culture,
Japan and a grant from the Sumitomo Foundation.
Notes and references
Scheme 1
1 (a) R. Schwesinger and H. Schlemper, Angew. Chem., Int. Ed. Engl.,
1987, 26, 1167–1169; (b) R. Schwesinger, H. Schlemper, C. Hasenfratz,
J. Willaredt, T. Dambacher, T. Breuer, C. Ottaway, M. Fletschinger,
J. Boele, H. Fritz, D. Putzas, H. W. Rotter, F. G. Bordwell, A. V. Satish,
G.-Z. Ji, E.-M. Peters, K. Peters, H. G. von Schnering and L. Walz,
Liebigs Ann., 1996, 1055–1081.
apparently functions as an activator. The use of dimethylzinc
instead of diethylzinc was not effective for the exchange reaction
and the reaction was sluggish.
2 J. G. Verkade and P. B. Kisanga, Tetrahedron, 2003, 59, 7819–7858.
3 (a) G. A. Kraus, N. Zhang, J. G. Verkade, M. Nagarajan and P. B.
Kisanga, Org. Lett., 2000, 2, 2409–2410; (b) T. Pietzonka and D. Seebach,
Chem. Ber., 1991, 124, 1837–1843; (c) T. Pietzonka and D. Seebach,
Angew. Chem., Int. Ed. Engl., 1993, 32, 716–717; (d) I. Leito, T. Rodima,
I. A. Koppel, R. Schwesinger and V. M. Vlasov, J. Org. Chem., 1997, 62,
8479–8483; (e) H. Schlaad, H. Kukula, J. Rudloff and I. Below,
Macromolecules, 2001, 34, 4302–4304; (f) T. Imahori and Y. Kondo,
J. Am. Chem. Soc., 2003, 125, 8082–8083; (g) T. Imahori, C. Hori and
Y. Kondo, Adv. Synth. Catal., 2004, 346, 1090–1092.
Using this exchange reaction, some functionalizations of aryl
halides were examined. As an example of 1,2-addition to a
carbonyl group, the arylzinc prepared from 1 and diethylzinc in the
presence of t-Bu-P4 base in THF was reacted with benzaldehyde to
give the benzhydrol derivative 3 in 78% yield. As for the 1,4-
addition reaction, the arylzinc prepared similarly in THF was
reacted with chalcone and the 1,4-adduct was obtained in 71%
yield under copper-free reaction conditions. Allylation was also
carried out in the absence of copper additive, and allylbenzoate 5
was obtained in 98% yield. Using the same reaction procedure, the
allyl arenes 6, 7, 8, 9 were prepared from the corresponding aryl
iodides in excellent yields. It has been reported that arylzinc
compounds are inert to 1,4-addition and allylation reaction in the
absence of additives and conventionally the employment of copper
species has been widely used.5 However, in this case the t-Bu-P4
base is considered to promote the reactivity of arylzinc compounds
toward electrophiles.
4 M. Ueno, C. Hori, K. Suzawa, M. Ebisawa and Y. Kondo, Eur. J. Org.
Chem., 2005, 1965–1968.
5 P. Knochel and P. Jones, Organozinc Reagents, Oxford University Press,
Oxford, 1999.
6 (a) F. F. Kneisel, M. Dochnahl and P. Knochel, Angew. Chem., Int. Ed.,
2004, 43, 1017–1021; (b) L.-Z. Gong and P. Knochel, Synlett, 2005,
267–270; (c) F. F. Kneisel, H. Leuser and P. Knochel, Synthesis, 2005,
2625–2629.
7 (a) Y. Kondo, N. Takazawa, C. Yamazaki and T. Sakamoto, J. Org.
Chem., 1994, 59, 4717–4718; (b) M. Uchiyama, M. Koike, M. Kameda
and Y. Kondo, J. Am. Chem. Soc., 1996, 118, 8733–8734; (c) Y. Kondo,
M. Shilai, M. Uchiyama and T. Sakamoto, J. Am. Chem. Soc., 1999, 121,
3539–3540; (d) T. Imahori, M. Uchiyama, T. Sakamoto and Y. Kondo,
Chem. Commun., 2001, 2450–2451; (e) M. Uchiyama, T. Miyoshi,
Y. Kajihara, T. Sakamoto, Y. Otani, T. Ohwada and Y. Kondo, J. Am.
Chem. Soc., 2002, 124, 8514–8515.
The arylzinc compounds prepared in DMF can also be used in
the palladium catalyzed Negishi coupling reaction8 and the reac-
tion of the arylzinc with iodobenzene in the presence of palladium
catalyst gave the corresponding biarylcarboxylated in 53% yield.
In summary, the use of t-Bu-P4 base as a promotor dramatically
improves the performance of the halogen–zinc exchange reaction
8 (a) E. Negishi, L. F. Valente and M. Kobayashi, J. Am. Chem. Soc.,
1980, 102, 3298–3299; (b) E. Negishi, Acc. Chem. Res., 1982, 15,
340–348.
3550 | Chem. Commun., 2006, 3549–3550
This journal is ß The Royal Society of Chemistry 2006