Scheme 2
the solvent and column chromatography over silica gel (3+7
hexane–EtOAc) gives pure 5, whose geometry in the solid state
was established by X-ray analysis. The reagent (1 mmol) reacts
smoothly with alcohols (1.1 mmol) in CH2Cl2 in the presence of
DCC (1.1 mmol) and DMAP (1.1 mmol) to give the
corresponding esters, after 1–26 h. Yields in these esterifica-
tions are generally high (see Table 1, entries 1–6 and 8–9). The
parent alcohol for 11 is a known compound,8,9 but one tentative
structural assignment given8 in the literature [(1-bromocyclo-
hexyl)methanol] is incorrect; our X-ray analysis of 11 estab-
lishes the actual structure. In one case (Table 1, entry 7) we
prepared the required starting ester by reaction of 5 (1.1 mmol)
with a THF solution of the alkene (1.0 mmol) in the presence of
NBS (1.1 mmol), and again the yield was high.
is present in the flowers of the tree Quararibea funebris (Llave).
Extracts of the flowers have been used14 by the Zapotec Indians
of Oaxaca, Mexico, to treat a number of disorders, including
some of a psychological nature, but it is not known whether 14c
itself is biologically active. It has been suggested that the
compound may be the biosynthetic precursor of several pyrrole
alkaloids present in the flower extract.14
All new compounds were characterized spectroscopically,
including high resolution mass measurements, except for 9b,
which was isolated as a mixture with 9a.
Acknowledgment is made to the Natural Sciences and
Engineering Research Council of Canada and to Merck Frosst
for financial support.
The radical cyclizations were done by slow addition (ca. 10
h, syringe pump) of separate toluene solutions of Bu3SnH (0.17
M, 1.5–2.5 mmol per mmol ester) and AIBN (0.012 M, 0.1–0.2
mmol per mmol ester) to a refluxing toluene solution of the ester
(1.0–1.8 mmol, 0.016 M). Refluxing was continued for an
arbitrary period of 2 h after the end of the addition. The products
were isolated in the yields indicated in Table 1, by evaporation
of the solvent and flash chromatography. While the oxime
geometry for 5, 11 and 14a was determined by X-ray analysis,
the geometries shown for the other oximes are arbitrary
assignments. All the cyclization products were single isomers,
except for 14a. In that example, the material was obtained
crystalline, and X-ray analysis showed the crystals to be
composed of the trans,E and cis,E isomers in a ratio of ca.
Notes and references
† No blue color was observed during the reaction. Tautomerization of a C-
nitroso compound, as the terminating step of an intermolecular reaction, is
known (see ref. 7)
1 Radical cyclizations of glyoxylic diphenylhydrazones and O-benzylox-
imes: D. L. J. Clive and J. Zhang, Chem. Commun., 1997, 549.
2 For intermolecular radical addition to a glyoxylic oxime ether, see: H.
Miyabe, C. Ushiro and T. Naito, Chem. Commun., 1997, 1789.
3 Recent examples involving O-methyl oximes: T. Naito, K. Nakagawa,
T. Nakamura, A. Kasei, I. Ninomiya and T. Kiguchi, J. Org. Chem.,
1999, 64, 2003; G. E. Keck, S. F. McHardy and A. Murry, J. Org.
Chem., 1999, 64, 4465.
4 Radical cyclizations involving oximes (and other nitrogen-containing
species) have been reviewed: A. G. Fallis and I. M. Brinza, Tetrahedron,
1997, 53, 17543.
1
55+45; the same composition was evident from the H NMR
spectrum. During cyclization of 9 a 1,2-acyloxy rearrange-
ment10 occurs, driven by formation of a benzylic radical.
We have examined briefly the partial reduction of several of
our a-oximino lactones. For example, treatment of 7a with iron
5 Homolytic C-alkylation of aldoximes: A. Citterio and L. Filippini,
Synthesis, 1986, 473.
6 For other radical sequences that result in CNN regeneration, see: G.
Pattenden and D. J. Schultz, Tetrahedron Lett., 1993, 34, 6787; S. Kim
and J. H. Cheong, Chem. Commun., 1998, 1143; S. Kim, I. Y. Lee, J.-Y.
Yoon and D. H. Oh, J. Am. Chem. Soc., 1996, 118, 5138; U. Iserloh and
D. P. Curran, J. Org. Chem., 1998, 63, 4711.
7 M. Kizil and J. A. Murphy, Tetrahedron, 1997, 53, 16847.
8 See footnote 23 in J. G. Traynham and W. G. Hines, J. Am. Chem. Soc.,
1968, 90, 5208.
9 M. Chini, P. Crotti, C. Gardelli and F. Macchia, Tetrahedron, 1992, 48,
3805.
10 A. L. J. Beckwith, D. Crich, P. J. Duggan and Q. Yao, Chem. Rev., 1997,
97, 3273.
11 Cf. D. H. R. Barton and S. Z. Zard, J. Chem. Soc., Perkin Trans. 1, 1985,
2191; M. J. Burke, G. Casy and N. B. Johnson, J. Org. Chem., 1998, 63,
6084; G. Zhu, A. L. Casalnuovo and X. Zhang, J. Org. Chem., 1998, 63,
8100.
12 R. F. Raffauf, T. M. Zennie, K. D. Onan and P. W. Le Quesne, J. Org.
Chem., 1984, 49, 2714.
13 For a structurally related natural product, see: A. J. Pallenberg and J. D.
White, Tetrahedron Lett., 1986, 27, 5591.
14 T. M. Zennie and J. M. Cassady, J. Nat. Prod., 1990, 53, 1611.
powder in Ac2O11 (room temperature, 14 h) gave a mixture of
enamide 7b (54%) and the doubly acetylated analog 7c (30%).
Under the same conditions, 11a gave 11b (80%), and no bis-
acetylated product was isolated.
Treatment of 14a with iron powder in TFAA gave enamide
14b (Scheme 2), the fluorinated anhydride being used because
we expected this choice to facilitate subsequent amide hydroly-
sis. In the event, treatment of 14b with aqueous K2CO3 afforded
enamine 14c, which is a naturally-occurring substance12,13 that
Communication a908842c
238
Chem. Commun., 2000, 237–238