8146 J . Org. Chem., Vol. 66, No. 24, 2001
Zhang et al.
F igu r e 1.
ties.8,9 Of particular note is that highly active and robust
metalloporphyrin catalysts with thousands of turnovers
can be obtained by introducing electron-withdrawing
groups or nonplanar distortion to the porphyrin ligand.6e
Recently, Collman and co-workers8i reported that a
pseudo C2-symmetric binaphthyl-strapped iron(III) por-
phyrin can effect enantioselective styrene oxidation with
up to 5500 turnovers.
Previously we reported the preparation of a dioxoru-
thenium(VI) complex containing the D4-symmetric tet-
rakis(dinorbornabenzene)-substituted porphyrin (D4-
H2Por* ) 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-
octahydro-1,2:5,8-dimethanoanthrance-9-yl]porphyrin, Fig-
ure 1) and its reactions with alkenes.9e,f This complex
reacts preferentially with cis-disubstituted alkenes such
as cis-â-methylstyrene under stoichiometric conditions to
give cis-epoxide in up to 72% ee.9f Later we found that a
series of D2-symmetric threitol-strapped dioxoruthenium-
(VI) porphyrin complexes can undergo facile epoxidation
of trans-â-methylstyrene with better enantioselectivity
than the analogous reactions with the cis-alkene.9j
The effectiveness of trans-dioxoruthenium(VI) porphy-
rins for stoichiometric alkene epoxidation has led us to
examine the application of ruthenium porphyrin for
catalytic organic oxidations. Indeed, ruthenium porphy-
rins are known to exhibit promising catalytic activities
toward organic oxidations using dioxygen,9e,10 N2O,11 or
2,6-dichloropyridine N-oxide (Cl2pyNO)12 as terminal oxi-
dant. Previously, Berkessal and co-workers9d communi-
cated the use of the [RuII(D4-Por*)(CO)(MeOH)] (2) cat-
alyst for enantioselective styrene epoxidation by Cl2-
pyNO. We and Gross also reported the use of other chiral
ruthenium(II) porphyrin derivatives for catalytic enan-
tioselective oxidation of trans-alkenes9h,j and alkanes13
by aromatic N-oxides. However, the catalytic reactions
with these chiral ruthenium(II) porphyrin catalysts are
slow and require long reaction time (ca. 48 h) for complete
substrate consumption. In this regard, we were attracted
to the work by Hirobe and co-workers12d,e that addition
of mineral acids (HCl/HBr) was found to enhance the
activities of the ruthenium porphyrin catalysts in the
alkane oxidations by aromatic N-oxide. In this work,
however, we found that addition of HBr to the “[RuII(D4-
Por*)(CO)] + Cl2pyNO” system in the styrene epoxidation
led to unsatisfactory yield and enantioselectivity, albeit
with complete substrate consumption within 3 h (see
later sections). Here we describe a new and highly
efficient enantioselective epoxidation of simple alkenes
under ambient conditions using a chiral dichlororuthe-
nium(IV) porphyrin, [RuIV(D4-Por*)Cl2] (1), as catalyst
and Cl2pyNO as terminal oxidant without the need for
an acid promoter.
(7) Selected examples on regio- and shape-selective epoxidations,
see: (a) Groves, J . T.; Nemo, T. E. J . Am. Chem. Soc. 1983, 105, 5786.
(b) Tabushi, I.; Morimitsu, K. J . Am. Chem. Soc. 1984, 106, 6871. (c)
Collman, J . P.; Brauman, J . I.; Meunier, B.; Hayashi, T.; Kodadek, T.;
Raybuck, S. A. J . Am. Chem. Soc. 1985, 107, 2000. (d) Groves, J . T.;
Neumann. R. J . Am. Chem. Soc. 1987, 109, 5045. (e) Collman, J . P.;
Zhang, X.; Hembre, R. T.; Brauman, J . I. J . Am. Chem. Soc. 1990,
112, 5356.
(8) Leading examples of chiral iron and manganese porphyrin-
catalyzed enantioselective epoxidations, see: (a) Groves, J . T.; Myers,
R. S. J . Am. Chem. Soc. 1983, 105, 5791. (b) Mansuy, D.; Battoni, P.;
Renaud, J . P.; Guerin, P. J . Chem. Soc., Chem. Commun. 1985, 155.
(c) O’Malley, S. Kodadek, T. J . Am. Chem. Soc. 1989, 111, 9176. (d)
Grove, J . T.; Viski, P. J . Org. Chem. 1990, 55, 3628. (e) Naruta, Y.;
Tani, F.; Ishihara, N.; Maruyama, K. J . Am. Chem. Soc. 1991, 113,
6865. (f) Halterman, R. L.; J an, S.-T. J . Org. Chem. 1991, 56, 5253.
(g) Knoishi, K.; Oda, K.-I.; Nishida, K.; Aida, T.; Inoue, S. J . Am. Chem.
Soc. 1992, 114, 1313. (h) Collman, J . P.; Zhang, X.-M.; Lee, V. J .;
Uffelman, E. S.; Brauman, J . I. Science 1993, 261, 1404. (i) Collman,
J . P.; Wang, Z.; Straumanis, A.; Quelquejeu, M. J . Am. Chem. Soc.
1999, 121, 460.
Resu lts a n d Discu ssion
P r ep a r a tion of th e Dich lor or u th en iu m (IV) P or -
p h yr in Ca ta lyst. Following the method reported by
Gross and co-workers,14a [RuII(D4-Por*)(CO)(MeOH)] (2)
(9) Chiral ruthenium-oxo complexes for enantioselective epoxida-
tions: (a) Fung, W.-H.; Cheng, W.-C.; Yu, W.-Y.; Che, C.-M.; Mak, T.
C.-W. J . Chem. Soc., Chem. Commun. 1995, 2007. (b) Cheng, W.-C.;
Yu, W.-Y.; Zhu, J .; Cheung, K.-K.; Peng, S.-M.; Poon, C.-K.; Che,
C.-M. Inorg. Chim. Acta 1996, 242, 105. (c) Gross, Z.; Ini, S. J . Org.
Chem. 1997, 62, 5514. (d) Berkessel, A.; Frauenkron, M. J . Chem. Soc.,
Perkin Trans. 1,1997, 2265. (e) Lai, T.-S.; Zhang, R.; Cheung K.-K.;
Kwong, H.-L.; Che, C.-M. Chem. Commun. 1998, 3559. (f) Lai, T.-S.;
Kwong, H.-L.; Zhang, R.; Che, C.-M. J . Chem. Soc., Dalton Trans. 1998,
1805. (g) Fung, W.-H.; Yu, W.-Y.; Che, C.-M. J . Org. Chem. 1998,
63, 7735. (h) Gross, Z.; Ini, S. Org. Lett. 1999, 1, 2077. (i) Yu, W.-Y.;
Fung, W.-H.; Zhu, J .-L.; Cheung, K.-K.; Ho, K.-K.; Che, C.-M. J . Chin.
Chem. Soc. 1999, 46, 341. (j) Zhang, R.; Yu, W.-Y.; Lai, T.-S.; Che,
C.-M. Chem. Commun. 1999, 409. (k) Gross, Z.; Ini, S. Inorg. Chem.
1999, 38, 1446.
(10) Grove, J . T.; Quinn, R. J . Am. Chem. Soc. 1985, 107, 5790.
(11) Groves, J . T.; Roman, J . S. J . Am. Chem. Soc. 1995, 117, 5594.
(12) For alkene epoxidations, see: (a) Higuchi, T.; Ohtake, H.;
Hirobe, M. Tetrahedron Lett. 1989, 30, 6545. (b) Higuchi, T.; Ohtake,
H.; Hirobe, M. Tetrahedron Lett. 1991, 32, 7435. (c) Ohtake, H.;
Higuchi, T.; Hirobe, M. Tetrahedron Lett. 1992, 33, 2521. For alkane
hydroxylations, see: (d) Ohtake, H.; Higuchi, T.; Hirobe, M. J . Am.
Chem. Soc. 1992, 114, 10660. (e) Higuchi, T.; Hirobe, M. J . Mol. Catal.
A 1996, 113, 403.
(13) Zhang, R.; Yu, W.-Y.; Lai, T.-S.; Che, C.-M. Chem. Commun.
1999, 1791.
(14) (a) Gross, Z.; Barzilay, C. M. J . Chem. Soc., Chem. Commun.
1995, 1287. For an earlier report on the preparation of dihalogenoru-
thenium(IV) porphyrin, see: (b) Ke, M.; J ames, B. R.; Dolphin, D.;
Sparapany, J . W.; Ibers, J . A. Inorg. Chem. 1991, 30, 4766.