Intramolecular Cyclisation/Cyclofragmentation of β-Substituted γ-Nitro Ketones
FULL PAPER
Yu. A. Strelenko, V. A. Tartakovsky, Tetrahedron Lett. 1999,
resulting ethereal solution was filtered in a dry atmosphere, and
the precipitate of DBU·HCl was washed with Et2O (5 mL). The
combined filtrate was concentrated in vacuo to give crystalline
nitronate 2 (96%) which was used in the following transformation
without further purification. Ϫ 1H NMR: δ ϭ 0.27 (s, 9 H, SiMe3),
2.05 (s, 3 H, Me), 2.87 (dd, 2J ϭ 16.6 Hz, 3J ϭ 7.1 Hz, 1 H,
40, 5075Ϫ5078.
[7]
[8]
The physical constants obtained for the oxime 7 are in com-
plete agreement with those described in the literature: P. Bravo,
G. Gaudiano, C. Ticozzi, A. Umani-Ronchi, Gazz. Chim. Ital.
1969, 99, 549Ϫ564.
A general procedure is described in the following article: J. M.
Aizpurua, M. Oiarbide, C. Palomo, Tetrahedron Lett. 1987,
28, 5361Ϫ5364.
M. A. Brook, D. Seebach, Can. J. Chem. 1987, 65, 836Ϫ850.
In early studies, Me3SiOTf has been reported to be ineffective
in promoting the addition of silyl enol ethers to regular nitro
alkenes: A. Yoshikoshi, M. Miyashita, Acc. Chem. Res. 1985,
18, 284Ϫ290.
2
CHAHB), 3.09 (dd, J ϭ 16.6 Hz, 3J ϭ 7.0 Hz, 1 H, CHAHB), 4.23
(m, 1 H, CHPh), 6.31 (d, 3J ϭ 7.2 Hz, 1 H, CHϭN), 7.12Ϫ7.30
(m, 5 H, Ph). Ϫ 13C NMR: δ ϭ Ϫ0.4 (SiMe3), 29.6 (Me), 38.5
(CHPh), 46.0 (CH2), 118.0 (CHϭN), 126.9 (CHp, Ph), 127.3 and
128.5 (CHo and CHm, Ph), 139.6 (Cipso, Ph), 204.8 (CϭO). Ϫ 29Si
NMR: δ ϭ 26.67. Ϫ 14N NMR: δ ϭ Ϫ97 (∆ν2 ഠ 1400 Hz).
[9]
[10]
[11]
Recently, 5,6-dihydro-4H-[1,2]oxazine-2-oxides were systemat-
ically studied and widely applied as 1,3-dipoles in highly stereo-
[11a]
Preparation of 2-Phenylpropenal Oxime (7): All the crude 6 ob-
tained from nitro compound 1 (see GP1) was dissolved in MeOH
(1 mL) and the mixture was stirred for 24 h at ambient temperature.
Then the volatile components were removed in vacuo, and the res-
idue was recrystallized from CH2Cl2/petroleum ether (1:7) to give
the product 7 (0.06 g, 41% isolated yield with respect to the starting
nitro ketone 1) as white crystals, m.p. 105Ϫ107 °C (ref.[7] m.p. 103
selective [3 ϩ 2] cycloadditions to CϭC double bonds:
S.
E. Denmark, A. Thorarensen, Chem. Rev. 1996, 96, 137Ϫ165.
[11b]
Ϫ
S. E. Denmark, E. A. Martinborough, J. Am. Chem.
[11c]
Soc. 1999, 121, 3046Ϫ3056; and to CϵC triple bonds:
D.
Seebach, I. M. Lyapkalo, R. Dahinden, Helv. Chim. Acta 1999,
82, 1829Ϫ1842.
Seemingly, the C4ϪH bond in the cyclic intermediate B is
sterically more accessible for the proton abstraction with Et3N
than the corresponding CβϪH bond in the open-chain ana-
logue A.
[12]
1
°C). Ϫ H NMR: δ ϭ 5.42 (s, 1 H, CH2), 5.50 (s, 1 H, CH2), 7.26
(br. s, 5 H, Ph), 7.86 (s, 1 H, CHϭN), 8.69 (s, 1 H, NOH). Ϫ 13C
NMR: δ ϭ 123.0 (CH2), 128.2 (CHp, Ph), 128.2 and 128.3 (CHo
and CHm, Ph), 137.4 (Cipso, Ph), 143.1 (CH2ϭC), 151.5 (CϭN).
[13] [13a]
P. Gygax, T. K. DasGupta, A. Eschenmoser, Helv. Chim.
[13b]
Acta 1972, 55, 2205Ϫ2214. Ϫ
E. Shalom, J.-L. Zenou, S.
Shatzmiller, J. Org. Chem. 1977, 42, 4213Ϫ4216. Ϫ [13c] R. Far-
agher, T. L. Gilchrist, J. Chem. Soc., Perkin Trans. 1 1979,
258Ϫ262. Ϫ [13d] B. Hardegger, S. Shatzmiller, Helv. Chim. Acta
1976, 59, 2765Ϫ2767.
[14]
[15]
Acknowledgments
We consider 5,6-dihydro-2-trimethylsilyloxy-2H-[1,2]oxazines
of type C to be essentially less stable than their 5,6-dihydro-2-
alkyl- or 5,6-dihydro-2-trialkylsilyl- analogues due to the desta-
bilizing effect of the three heteroatoms in the OϪNϪO frag-
ment. This effect may complicate their isolation or even obser-
vation by NMR spectroscopy.
The stereochemical outcome of the [4 ϩ 2] cyclofragmentation
of E depends strongly on the stereoisomer ratio of the starting
cyclic nitronate 8. The variation of isomer ratios of 8 can be
achieved by means of solvent modification in its synthesis (see
ref.[11c]). Thus, the silylation of 8 (as a 1:3:5.8:20.5 mixture of
isomers) leads to a 1:4 mixture of (Z)-9 and (E)-9 (overall yield
86%), respectively, whereas the treatment of 8 (as a 1:27:4:16
mixture) with the same Me3SiBr/Et3N gives rise to 9 as a 1.4:1
mixture of (Z)-9 and (E)-9 in 70% yield. Since the geometry of
the formation of CϭC bonds could testify to the mechanism
of the [4 ϩ 2] cyclofragmentation of intermediate E, the investi-
gation of this problem requires separate efforts in the near fu-
ture. The configuration of the CHϭNOSiMe3 group in both
isomers of 9 was not determined, but it is equal according to
NMR spectroscopic data.
M. Hesse, H. Meier, B. Zeeh, Spektroskopische Methoden in der
Organischen Chemie, Georg. Thieme Verlag, Stuttgart, 1995,
108 (in German).
This is the usual way of transforming γ-functionalized aliphatic
nitro compounds in the absence of branching at the β-carbon
atom (see ref.[5d]).
The observed difference of reactivity of γ-benzoyl and γ-acetyl
nitro compounds is difficult to explain unambiguously now-
adays. The collected experimental results of the silylation of
substituted nitro aliphatics reveal that the reaction mechanisms
are usually very complex and frequently vary, although high
chemoselectivity is normally observed in each case. We are now
studying the silylation of nitro compounds of general type
R1C(O)CH2CH(R2)CH2NO2 with a wide variation of R1 and
R2. The summarized results will be published in due course.
G. E. Morris, R. Freeman, J. Am. Chem. Soc. 1979, 101,
760Ϫ762.
This work was performed at the Scientific Educational Center for
young chemists and supported by the Russian Foundation of Basic
Research (grants NN 98Ϫ03Ϫ33002a, 96Ϫ15Ϫ97332), and the
Federal Program ‘‘Integration’’ (project No. A0082). We thank
Mr. B. G. Kimel for his help with the search for bibliographic in-
formation.
[1]
S. L. Ioffe, I. M. Lyapkalo, L. M. Makarenkova, J. Org. Chem.
Russ. 1998, 34, 1141Ϫ1148 (Russ.); Russ. J. Org. Chem. 1998,
34, 1085Ϫ1092 (Engl. transl.)
For an early short review article devoted to the chemistry of
[2]
N,N-bis(lithioxy)enamines (so-called ‘‘superenamines’’), see: R.
E. Marti, D. Seebach, Encyclopedia of Reagents for Organic
Synthesis, (Ed.: L. Paquette) Wiley, New York, 1995, 3,
1946Ϫ1948; Encyclopedia of Reagents for Organic Synthesis,
(Ed.: L. Paquette) Wiley, New York, 1995, 5, 3551Ϫ3552.
[3]
For the synthesis and reactivity of N,N-bis(trialkylsilyloxy)ena-
mines (BENA), see: [3a]H. Feger, G. Simchen, Liebigs Ann.
1986, 1456Ϫ1465. Ϫ [3b]A. D. Dilman, A. A. Tishkov, I. M.
Lyapkalo, S. L. Ioffe, Yu. A. Strelenko, V. A. Tartakovsky, Syn-
thesis 1998, 181Ϫ185. Ϫ [3c]H. Feger, G. Simchen, Lieb. Ann.
Chem. 1986, 428Ϫ437. Ϫ [3d]A. D. Dilman, I. M. Lyapkalo,
Yu. A. Strelenko, S. L. Ioffe, V. A. Tartakovsky, Mendeleev
Commun. 1997, 133Ϫ135. Ϫ [3e]A. D. Dilman, I. M. Lyapkalo,
S. L. Ioffe, Yu. A. Strelenko, V. A. Tartakovsky, Synthesis
1999, 1767Ϫ1775.
[16]
[17]
[18]
[4]
S. L. Ioffe, I. M. Lyapkalo, A. A. Tishkov, V. M. Danilenko,
Yu. A. Strelenko, V. A. Tartakovsky, Tetrahedron 1997, 53,
13085Ϫ13098.
[5a] S. L. Ioffe, V. A. Tartakovsky, V. M. Danilenko, Yu. A Stre-
[5]
lenko, VI Int. Conf. on Org. Synth. Abstr. of papers. Moscow,
[5b]
1986, 48. Ϫ
V. M. Danilenko, S. L. Ioffe, Yu. A. Strelenko,
[19]
N. F. Karpenko, A. V. Kalinin, V. A. Tartakovsky, Bull. Acad.
Sci. USSR. Div. Chem. Sci. 1987, 2638Ϫ2639 (Russ.); 1987,
[5c]
[20]
[21]
2453Ϫ2454 (Engl. transl.). Ϫ
S. L. Ioffe, V. M. Danilenko,
M. C. Kloetzel, J. Am. Chem. Soc. 1947, 69, 2271Ϫ2275.
Obtained by silylation of acetone with Me3SiCl/Et3N in DMF
in the conditions specified for butan-2-one in ref.[22]
H. O. House, L. J. Czuba, M. Gall, H. D. Olmstead, J. Org.
Chem. 1969, 34, 2324Ϫ2336.
Yu. A. Strelenko, V. A. Tartakovsky, J. Org. Chem. Russ. 1995,
31, 1253Ϫ1254 (Russ.); Russ. J. Org. Chem. 1995, 31,
[5d]
[22]
1144Ϫ1145 (Engl. transl.). Ϫ
A. A. Tishkov, I. M. Lyap-
kalo, S. L. Ioffe, Yu. A. Strelenko, V. A. Tartakovsky, Russ.
Chem. Bull. 1997, 46, 205Ϫ206.
Received February 23, 2000
[6]
A. A. Tishkov, A. V. Kozintsev, I. M. Lyapkalo, S. L. Ioffe,
[O00081]
Eur. J. Org. Chem. 2000, 3229Ϫ3233
3233