K. Fujita et al. / Tetrahedron Letters 47 (2006) 4831–4834
4833
Obora, Y.; Tokunaga, M.; Sato, H.; Tsuji, Y. Chem.
Commun. 2005, 4526–4528; (c) Fan, G.-H.; Chen, Y.-M.;
Chen, X.-M.; Jiang, D.-Z.; Xi, F.; Chan, A. S. C. Chem.
Commun. 2000, 789–790; (d) Bhyrappa, P.; Young, J. K.;
Moore, J. S.; Suslick, K. S. J. Am. Chem. Soc. 1996, 118,
5708–5711.
of 3(Gn[Me]) and 3(Gn[Bn]), the chemical yield of an
adduct was enhanced by increasing the generation of
the dendritic Cu(OTf)2 catalyst. This relationship
between the generation of the dendritic catalyst and
the chemical yield is one of the positive dendritic
effects.5,6,14
7. Previously reported 2,20-bipyridine core dendrimers: (a)
Hong, Y.-R.; Gorman, C. B. J. Org. Chem. 2003, 68,
9019–9025; (b) Tyson, D. S.; Luman, C. R.; Castellano, F.
N. Inorg. Chem. 2002, 41, 3578–3586; (c) Issberner, J.;
Vogtle, F.; Cola, L. D.; Balzani, V. Chem. Eur. J. 1997, 3,
706–712.
8. (a) Tomoyose, Y.; Jiang, D.-L.; Jin, R.-H.; Aida, T.;
Yamashita, T.; Horie, K.; Yashima, E.; Okamoto, Y.
Macromolecules 1996, 29, 5236–5238; (b) Hawker, C. J.;
Frechet, J. M. J. J. Am. Chem. Soc. 1990, 112, 7638–
7647.
9. Selected date: 3(G2[Me]) white powder; mp 151.5–
152.5 °C; mmax(CH2Cl2)/cmꢀ1 3001, 2937, 2838, 1597,
1458, 1374, 1296, 1230, 1204, 1155, 1055, 833; dH
(500 MHz; CDCl3; Me4Si) 3.79 (24H, s, OCH3), 4.99
(8H, s, outer-CH2), 5.15 (4H, s, inner-CH2), 6.41 (4H, t, J
2.2, ArH), 6.59–6.57 (10H, m, ArH), 6.69 (4H, d, J 2.2,
ArH), 6.88 (2H, dd, J 5.6 and 2.7, 5,50-bipyridine-H), 8.06
(2H, d, J 2.7, 3,30-bipyridine-H), 8.47 (2H, d, J 5.6, 6,60-
bipyridine-H); dC (125 MHz; CDCl3; Me4Si) 55.3, 69.7,
70.1, 100.0, 101.9, 105.2, 106.4, 107.1, 111.4, 138.2, 139.0,
150.2, 157.8, 160.1, 161.0, 165.7; m/z (FAB) 1033.5
([(M+H)]+ C60H61N2O14 requires 1033.4); Anal. Calcd
for C60H60N2O14: C, 69.75; H, 5.85; N, 2.71. Found: C,
69.74; H, 6.03; N, 2.60.
On the other hand, the negative dendritic effect in the
Diels–Alder reaction caused by employing the dendritic
bis(oxazoline)-Cu(OTf)2 catalyst has previously been re-
ported by the other group.15 They reported that the rea-
son of their negative dendritic effect was due to the steric
hindrance of its bulky dendritic skeleton. We assume
that our profound dendritic effect is probably derived
from the increase of the Lewis acidity due to the dis-
torted bipyridine skeleton of the 3-Cu(OTf)2 complex
by the steric repulsion of the dendritic wedges,16 thus
affording better chemical yield with increasing the gener-
ation of the dendrimer.6c Exactly, by the comparison of
the chemical yields in the same generation, 3(Gn[Bn]),
which possesses bulkier groups at its periphery, affords
better chemical yields than 3(Gn[Me]) in all generations.
We are currently trying to apply this dendritic ligand to
other catalytic conversions and to apply these catalytic
processes to a continuous-flow membrane reactor by
nanofiltration. The results will be reported in due
course.
10. (a) Freeman, A. W.; Chrisstoffels, L. A. J.; Frechet, J. M.
J. J. Org. Chem. 2000, 65, 7612–7617; (b) Forier, B.;
Dahaen, W. Tetrahedron 1999, 55, 9829–9846.
Acknowledgements
11. Previously reported Cu(OTf)2-catalyzed Diels–Alder reac-
tion: (a) Hertweck, C. J. Pract. Chem. 2000, 342, 316–321;
(b) Sagasser, I.; Helmchen, G. Tetrahedron Lett. 1998, 39,
261–264; (c) Brunel, J. M.; Campo, B. D.; Buono, G.
Tetrahedron Lett. 1998, 39, 9663–9666; (d) Carbone, P.;
Desimoni, G.; Faita, G.; Filippone, S.; Righetti, P.
Tetrahedron 1998, 54, 6099–6110; (e) Evans, D. A.; Miller,
S. J.; Lectka, T. J. Am. Chem. Soc. 1993, 115, 6460–
6461.
This work was supported by Industrial Technology
Research Grant Program in ’04 from New Energy and
Industrial Technology Development Organization
(NEDO) of Japan and by a Grant-in-Aid for Scientific
Research from Japan Society for the Promotion of
Science.
12. General procedure: The dendritic Lewis acid catalyst was
prepared by treatment of Cu(OTf)2 (0.03 mmol) with
3(G2[Me]) (0.03 mmol) at room temperature in dry
dichloromethane (1.5 mL) for 2 h under an argon atmo-
sphere. To the resulting bluish green solution of the
catalyst was added a mixture of diene (1.5 mmol) and
dienophile (0.3 mmol) in dry dichloromethane (1.5 mL) at
0 °C under an argon atmosphere. The resulting mixture
was stirred for 2–16 h at room temperature (monitored by
TLC). It was then quenched with water and was subjected
to the usual extractive workup with dichloromethane. The
residual oil obtained after evaporation of dichlorometh-
ane, which was dried over magnesium sulfate, was purified
by column chromatography on silica gel to give the
corresponding Diels–Alder adducts.
References and notes
1. (a) Dendrimers and Other Dendritic Polymers; Frechet, J.
M. J., Tomalia, D. A., Eds.; John Wiley & Sons: New
York, 2001; (b) Newkome, G. R.; Moorefield, C. N.;
Vogtle, F. Dendrimers and Dendrons; Wiley-VCH: Wein-
heim, 2001.
2. (a) Dijkstra, H. P.; van Klink, G. P. M.; van Koten, G.
Acc. Chem. Res. 2002, 35, 798–810; (b) van Heerbeek, R.;
Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek, J. N.
H. Chem. Rev. 2002, 102, 3717–3756.
3. (a) Grayson, S. M.; Frechet, J. M. J. Chem. Rev. 2001,
101, 3819–3867; (b) Astruc, D.; Chardac, F. Chem. Rev.
2001, 101, 2991–3023.
13. Narasaka, K.; Iwasawa, N.; Inoue, M.; Yamada, T.;
Nakashima, M.; Sugimori, J. J. Am. Chem. Soc. 1989, 111,
5340–5345.
4. (a) Kreiter, R.; Kleij, A. W.; Gebbink, R. J. M. K.; van
Koten, G. Top. Curr. Chem. 2001, 217, 163–199; (b)
Oosterom, G. E.; Reek, J. N. H.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. 2001, 40,
1828–1849.
5. (a) Fujita, K.; Muraki, T.; Sakurai, T.; Oishi, A.; Taguchi,
Y. Chem. Lett. 2005, 34, 1180–1181; (b) Muraki, T.;
Fujita, K.; Oishi, A.; Taguchi, Y. Polym. J. 2005, 37, 847–
853.
14. Previously reported positive dendritic effects caused by the
periphery-catalyzed dendrimers: (a) Benito, J. M.; de
Jesus, E.; de la Mata, F. J.; Flores, J. C.; Gomez, R. Chem.
Commun. 2005, 5217–5219; (b) Delort, E.; Darbre, T.;
Reymond, J.-L. J. Am. Chem. Soc. 2004, 126, 15642–
15643; (c) Ribourdouille, Y.; Engel, G. D.; Richard-
Plouet, M.; Gade, L. H. Chem. Commun. 2003, 1228–1229;
(d) Dahan, A.; Portnoy, M. Org. Lett. 2003, 5, 1197–1200;
6. (a) Helms, B.; Liang, C. O.; Hawker, C. J.; Frechet, J. M.
J. Macromolecules 2005, 38, 5411–5415; (b) Fujihara, T.;