August 1998
SYNLETT
933
Cu(I)-Binaphthyldiimine Catalyzed Asymmetric Cyclopropanation of Olefin with
Diazoacetate
1)
Hiroyuki Suga,* Tomomi Fudo, and Toshikazu Ibata*
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560, Japan
Received 28 May 1998
Abstract: Chiral 1,1’-binaphthyl-N,N’-bis(2,6-dichloro-benzy-lidene)-
2,2’-diamine (1) was found to be an effective ligand for the
copper-catalyzed enantioselective cyclopropanation of olefin with l-
menthyl diazoacetate. For example, the reaction of 1,1-diphenylethylene
with l-menthyl diazoacetate in the presence of CuOTf-1 complex in
(entries 2 and 3). Several kinds of (R)-1,1'-binaphthyl-2,2'-diimines 2 –
6 were synthesized and were used as the ligands for asymmetric
cyclopropanation of styrene with l-menthyl diazoacetate under similar
conditions (entries 4 – 8). However, higher enantioselectivity than that
using 1 was not obtained. These results suggest that not only bulkiness
of 2,6-substituents of benzene ring but also electronic character
influence the enantioselectivity. It is quite noteworthy that the selectivity
was improved especially for cis-adduct 8c by diluting the solution of
l-menthyl diazoacetate (entries 9, 10 and 14) in comparison with the
selectivity under the concentration of entry 3. However, slow addition of
the solution of l-menthyl diazoacetate did not improve the selectivity.
This means that proper low concentration is needed for good selectivity
(entry 11). Amounts of the catalyst did not significantly affect the
enantioselectivity (entries 9, 10, and 15). In the case of using (S)-ligand
instead of (R)-ligand, selectivity of trans-adduct was slightly decreased
probably due to stereochemical mismatching between (S)-catalyst and l-
menthyl diazoacetate (entry 12).
CH Cl at – 40 °C gave the corresponding cyclopropanecarboxylate in
2
2
98% ee.
The metal-catalyzed cyclopropanation of alkenes with diazo compounds
is an important synthetic reaction. In 1966, Nozaki and co-workers
reported the first example of enantioselective cyclopropanation of
styrene with diazoacetate catalyzed by chiral bis[N-α-
2)
phenylethylsalicylaldiminato]Cu(II) in less than 10% ee. After that
discovery, various kinds of optically active transition metal complexes
have been synthesized and high enantioselectivity has been reported by
3)
4)
5)
using Cu-Schiff base, Cu-semicorrin, Cu-bis(oxazoline), Cu-
6)
7)
8)
9)
bipyridine, Co-bis(dioxime), Co-Salen, Rh (5S-MEPY) , and
complexes as catalyst. However, there has been no
example concerning the catalyst only having axial chirality.
2
4
Using easily handled Cu(MeCN) PF as copper salt in the asymmetric
10)
4
6
Ru-Pybox
cyclopropanation of styrene with l-menthyl diazoacetate afforded
similar degree of enantioselectivity (entry 16) compared with that
11)
To
evaluate the role of axial chirality in asymmetric induction of the
carbenoid, we examined the cyclopropanation. In this paper, we report
the asymmetric cyclopropanation of olefin with diazoacetate catalyzed
utilizing CuOTf. However, Cu(OTf) -1 complex catalyzed
2
decomposition of l-menthyl diazoacetate in the presence of styrene gave
unsatisfactory result in terms of enantioselectivity of trans- and cis-
cyclopropanes (entry 17).
12)
by Cu(I)- and Cu(II)-1,1'-binaphthyl-2,2'-diimine complexes having
axial chirality.
We applied asymmetric cyclopropanation with Cu(I)-1 complex to other
olefins (entries 18 – 30) with l-menthyl diazoacetate under the same
conditions as styrene (entries 10 and 16). The reaction of 2-
vinyl-naphthalene,
α-methylstyrene,
2-methyl-1-propene,
and
methylenecyclohexane showed moderate enantioselectivity (entries 18 –
19, and 28 – 30). On the other hand, it is interesting to note that the
reaction of 1,1-diaryl substituted ethylenes (entries 20 –27) showed
extremely high enantioselectivity (up to 98%ee). The enantioselectivity
of the 1-CuOTf catalyzed reaction of 1,1-diphenylethylene was quite
dependant on the reaction temperature. Although only 74% ee was
observed under the conditions at rt (entry 20), the enantioselectivity
increased by decreasing the temperature (entries 21 – 23) and at – 40 °C
the corresponding cyclopropane was obtained in 98 % ee with high
chemical yield (entry 23). In the case of using Cu(MeCN) PF -1
4
6
complex as catalyst, 93% ee was obtained even at rt (entry 24). The high
enantioselectivity of the reaction was not affected by electronic
character of the substituent on phenyl group of 1,1-diaryl substituted
ethylene (entries 26 and 27).
Typical experimental procedure was exemplified by the reaction of
1,1-diphenylethylene with l-menthyl diazoacetate: To a suspension of
copper(I) trifluoromethanesulfonate benzene complex (CuOTf•0.5
We prepared (R)-1,1'-binaphthyl-2,2'-diimine 1 by the reaction of
(R)-1,1'-binaphthyl-2,2'-diamine with 2,6-dichlorobenzaldehyde and
13)
C H , 14 mg, 0.055 mmol) in dry CH Cl (5.0 mL) was added a
6 6 2 2
examined the Cu(I)-1 complexes in asymmetric cyclopropanation (Table
1, entry 1). To a solution of styrene (5 equiv) and the CuOTf-1 complex
solution
of
(R)-1,1'-binaphthyl-N,N'-(2,6-dichlorobenzylidene)-
2,2'-diamine (1) (35 mg, 0.058 mmol) in dry CH Cl (7.5 mL) at room
2
2
(1 mol%) in CH Cl was added a solution of ethyl diazoacetate in
temperature under argon atmosphere. After stirring for 1 h,
2
2
CH Cl over a period of 6 h and then the mixture was stirred for 16 h at
1,1-diphenylethylene (2.44 mL, 13.8 mmol) was added to the mixture.
2
2
room temperature (rt). The corresponding cyclopropanes 7a and 8a
were obtained in 75% yield in a ratio of trans : cis = 79 : 21 with 34% ee
(trans) and 47% ee (cis). Increases in bulkiness of ester groups resulted
in increases of enantioselectivity of trans-cyclopropane 7 as generally
observed in asymmetric cyclopropanation of olefin with diazoacetate
The mixture was cooled to – 40 °C and a solution of l-menthyl
diazoacetate (0.617 g, 2.75 mmol) in CH Cl (5.0 mL) was added to the
2
2
mixture over a period of 6 h. The mixture was stirred for 16 h and then
concentrated in vacuo. The residue was chromatographed on silica gel
(hexane : ethyl acetate = 99 : 1) to give 0.859 g (83% yield) of the
Suga, Hiroyuki
