1272
LETTERS
SYNLETT
(Entries 8 and 9). In Entries 2, 3 and 6-9, the formation of various by-
products such as the ketone and the bis(hydroxyimino) compound as
described above resulted in the decrease of the desired oximes. In
addition, (E)-6-hydroxyiminoandrost-4-ene-3,17-dione and (E)-6-
hydroxyiminoandrosta-1,4-diene-3,17-dione, which were known as
novel types of aromatase inhibitors,5) could be synthesized in one step
from easily available androstane derivatives6) by the present reduction-
nitrosation (Entries 10 and 11). To our knowledge, the present reaction
enables firstly the direct conversion of α,β,γ,δ-unsaturated carbonyl
compounds into γ-hydroxyimino-α,β-unsaturated ones.
Thus, a widely applicable method for the preparation of oximes from
conjugated olefins by cobalt(II) porphyrin-catalyzed reduction-
nitrosation was established.
References and Notes
(1) Okamoto, T.; Kobayashi, K.; Oka, S.; Tanimoto, S. J. Org. Chem.
1987, 52, 5089. Okamoto, T.; Kobayashi, K.; Oka, S.; Tanimoto,
S. J. Org. Chem. 1988, 53, 4897.
(2) Kato, K.; Mukaiyama, T. Chem. Lett. 1990, 1917. Kato, K.;
Mukaiyama, T. Chem. Lett. 1990, 1395. Kato, K.; Mukaiyama, T.
Bull. Chem. Soc. Jpn. 1991, 64, 2948.
(3) Matsushita, Y.; Matsui, T.; Sugamoto, K. Chem. Lett. 1992, 1381.
Matsushita, Y.; Sugamoto, K.; Matsui, T. Chem. Lett. 1992, 2165.
Matsushita, Y.; Sugamoto, K.; Matsui, T. Chem. Lett. 1993, 925.
Matsushita, Y.; Sugamoto, K.; Nakama, T.; Sakamoto, T.; Matsui,
T. Tetrahedron Lett. 1995, 36, 1879. Matsushita, Y.; Sugamoto,
K.; Nakama, T.; Matsui, T. J. Chem. Soc., Chem. Commun. 1995,
567.
(4) Wieland, T.; Grimm, D. Ber. 1963, 96, 275.
(5) Holland, H. L.; Kumaresan, S.; Tan, L.; Njar, V. C. O. J. Chem.
Soc., Perkin Trans 1 1992, 585. In this work, (E)-6-hydroxy-
iminoandrosta-4-ene-3,17-dione
and
(E)-6-hydroxyimino-
androsta-1,4-diene-3,17-dione were synthesized from ∆5-
androstene-3β,17β-diacetate by multi-step procedures.
(6) Androsta-4,6-diene-3,17-dione and androsta-1,4,6-triene-3,17-
dione were prepared form ∆4-androstene-3,17-dione in 64 % and
41 % yields, respectively, according to the following literature.
Pradhan, S. K.; Ringold, H. J. J. Org. Chem. 1964, 29, 601.
(7) Typical procedure for the reaction of 4-carbomethoxystyrene
1: The reaction was carried out under Ar in order to prevent any
contamination from O2. 1 (162 mg, 1 mmol) and CoII(tpp) (2.02
mg, 0.003 mmol) were dissolved in 3 cm3 of CH2Cl2 in a 50 cm3
kjeldahl flask equipped with three-way cock. The atmosphere in
the flask was replaced with Ar by bubbling for 15 min at O ºC,
and then an Ar balloon was attached to the flask through the three-
way stopcock. Triethylsilane (0.48 cm3, 3 mmol) and t-butyl
nitrite (0.36 cm3, 3 mmol) were dissolved in 2.0 cm3 of CH2Cl2
and 2.5 cm3 of i-PrOH followed by the replacement with Ar by
bubbling for 15 min at O ºC. The thus obtained mixture was added
to the solution of 1 and CoII(tpp), and then the mixture was stirred
at room temperature for 48 h. After removing the solvent under
reduced pressure, the residue was purified by silica gel column
chromatography with n-hexane / ethyl acetate (20/1 - 9/1 v/v) to
afford 4-carbomethoxyacetophenoxime 2 (169 mg, 87 %) and 4-
carbomethoxyacetophenone 3 (19.2 mg, 11 %).
phenylhydroxylaminyl ester and N-hydroxysuccinimidyl ester, the
desired hydroxyimino compounds were obtained in high yields (Entries
4 and 5). The yield of the hydroxyimino compounds seemed to increase
in order of increasing electron-negativity of the ester moiety. The results
of reduction-nitrosation of α,β,γ,δ-unsaturated amide and ketone were
similar to that of Entry 1, that is, the moderate yields of the
hydroxyimino esters and the recovery of the substrates unaltered were
observed (Entries 6 and 7). On the other hand, the reaction of 2,4-
hexadienal and 2,4-octadienonitrile afforded 4-hydroxyimino-2-hexenal
and 4-hydroxyimino-2-octenonitrile, respectively, in fairly good yields