Catalytic cyclopropanation and aziridination of alkenes by a Cu(I) complex of ferrocenyldiimine

Article abstract of DOI:10.1055/s-1998-1743

The copper(I) complex (FcNN)Cu(OTf) (1; FcNN = N,N′-ethylenebis[(ferrocenylmethylene)amine] catalyzes reactions of ethyl diazoacetate with alkenes to form cyclopropanes in high yield. The same complex also catalyzes nitrene transfer from PhI=NTs to alkene

Full text of DOI:10.1055/s-1998-1743

June 1998
SYNLETT
617
Catalytic Cyclopropanation and Aziridination of Alkenes by a Cu(I) Complex of
Ferrocenyldiimine
Dong-Jei Cho, Sang-Jin Jeon, Hong-Seok Kim, Tae-Jeong Kim*
Department of Industrial Chemistry, Kyungpook National University, Taegu 702-701, Korea
Fax 53-950-6594; e-mail: tjkim@kyungpook.ac.kr
Received 3 March 1998
Abstract: The copper(I) complex (FcNN)Cu(OTf) (1; FcNN = N,N’-
ethylenebis[(ferrocenylmethylene)amine] catalyzes reactions of ethyl
diazoacetate with alkenes to form cyclopropanes in high yield. The
same complex also catalyzes nitrene transfer from PhI=NTs to alkenes
to produce aziridines in high yield.
Catalytic C- and N-atom transfer to olefins leading to cyclopropanes
and aziridines, respectively, have attracted much research endeavour
1
due to their presence in numerous biomolecules. Consequently last
decade has seen development of a great number of catalysts capable of
such transformation. Palladium-, rhodium-, and copper-based systems
are reported to be the most efficient, with regard to both yields and
2
diastereo- and enantioselectivity. In particular, copper catalysts deserve
a special note in that soluble copper complexes incorporating chiral
Schiff bases such as salicylaldehyde derivatives, oxazolines,
semicorrins, polypyrazoles, etc. have achieved asymmetric
3
4
cyclopropanation and aziridination with moderate to high % de and %
ee.
As part of our ongoing project on the design of new ferrocene-
containing ligands and their applications to catalytic reactions and
asymmetric reactions, we have recently demonstrated that a ferrocene-
based Schiff base such as FcNN and its derivatives are efficient ligands
Finally, in connection with the reactions of trans-stilbene and
cyclohexenone, it is worth noting that this is one of the rare cases where
the high yield synthesis of cyclopropanated products can be achieved
using these compounds as substrate (entries 7-8). trans-Stilbene, for
5
for metal complexes in some catalytic reactions.
example, does not even react under the same copper catalysis with
4e
Tp’Cu(C H ) (Tp’ = hydridotris(3,5-dimethyl-1-pyrazolyl)borate). In
2
4
general, a sterically hindered approach of the trans-disubstituted alkene
to the presumed copper carbene complex intermediate may account for
the lack of reactivity of trans-stilbene.
The catalytic capabilities of (FcNN)Cu(OTf) are not restricted to
We now wish to report results which show that the copper(I) complex of
this ligand is also a highly efficient catalyst, under very mild conditions,
for carbene transfer from ethyl diazoacetate to alkenes to form
cyclopropanes. Furthermore, complex 1 also catalyzes, again under mild
conditions, nitrene transfer from PhI=NTs to alkenes to produce
p-
carbene transfer processes. Table 2 shows that alkenes and [(
7
tolylsulfonyl)imino]phenyliodinane, PhI=NTs, produce aziridines in
8
high yields when 1 is employed as catalyst (eq 2).
aziridines.
6
In
a
typical experiment, styrene was converted into ethyl 2-
phenylcyclopropane-1-carboxylate by using ethyl diazoacetate (EDA)
as the carbene source and a catalytic amount of 1 (1 mol% based on
EDA), as depicted in eq 1. The formation of byproducts such as diethyl
fumarate and maleate resulting from carbene dimerization was almost
negligible as confirmed by GC analysis.
Table 1 shows the results of cyclopropanation of a range of alkenes
differing in steric and electronic properties. Regardless of the type of
alkene, all reactions went to completion to achieve a 100% substrate
conversion (nitrogen evolution) within 10 h. Mono- and gem-
disubstituted terminal olefins (entries 1-5) display similar reactivities
with yields slightly higher than those obtained from internal olefins
(entries 6-9). The ratio of trans- to cis-diastereomers formed was found
to be approximately 60:40 for terminal olefins except for
methoxypropene which affords exclusively the trans (E) isomer (entry
5). The high preference for the trans product was also found with an
internal olefin such as cyclohexene which gives the trans-to-cis ratio of
95:5 (entry 6).
Again all reaction went to completion to achieve a 100% substrate
conversion within 2 h at room temperature as checked by GC. The
catalytic efficiency of 1 is nearly comparable to that of other well-
known catalysts reported in the literature.
All in all, (FcNN)Cu(OTf) is an efficient Cu(I) catalyst which functions
under mild conditions to transfer :CHCO Et and :NSO C H CH to
2
2
6
4
3

618
LETTERS
SYNLETT
alkenes to form cyclopropanes and aziridines. An asymmetric version of
this work by introduction of chirality into FcNN is in progress.
g) Lowenthal, R. E.; Abiko, A.; Masamune, S. Tetrahedron Lett.
1990, 31, 6005.
4.
a) Li, Zhen; Quan, R. W.; Jacobsen, E. N. J. Am. Chem. 1995, 117,
5889.
Acknowledgment: TJK gratefully acknowledges KOSEF (97-05-01-
b) Evans, D. A.; Faul, M. M.; Bilodeau, M. J. Am. Chem. 1994,
116, 2742.
05-01-3) and the Ministry of Education (Grant No. BSRI-97-3403).
c) Evans, D. A.; Faul, M. M.; Bilodeau, M. T.; Anderson, B. A.;
Barnes, D. M. J. Am. Chem. Soc. 1993, 115, 5328.
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1993, 115, 5326.
e) Perez, P. J.; Brookhart, M.; Templeton, J. L. Organometallics
1993, 12, 261
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-2
Alkene cyclopropanation: complex 1 (18 mg, 2.6 x 10 mmol)
was dissolved in 10 mL of 1,2-dichloroethane, and 5 equiv of the
olefin was added. Ethyl diazoacetate (2.6 mmol) was diluted in 10
mL of 1,2-dichloroethane and added slowly (5 h) with a syringe
pump to the [Cu]-alkene mixture. After stirring for 5 additional
hours at RT, solvent and excess olefin were removed under
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chromatography on silica gel to elute the products.
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-3
Aziridination reactions: complex 1 (5.7 mg, 8.1 x 10 mmol) was
placed in a Schlenk flask along with dry acetonitrile (2 mL).
Olefin (10 equiv) was added via a syringe, and the mixture was
-1
stirred for 15 min. PhI=NTs (100 mg, 2.7 x 10 mmol) was then
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added portionwise over 30 min. After stirring for 1-2 h at RT, the
mixture was applied to a vacuum line to remove any volatiles.
Column chromatography of the residue (4:1 hexane-EtOAc) led to
the isolation of the products as white crystalline solids.