D. Nauduri, A. Greenberg / Tetrahedron Letters 45 (2004) 4789–4793
4793
epoxide 16 (syn or anti): d 4.07, d, J ¼ 2:5 Hz, 1H; d
5.30, br s, 1H; d 5.64, d, J ¼ 2:5 Hz, 1H; 7.2–7.7, m, 4H;
d 9.60, br s, 1H. There was also a much smaller peak at d
9.77 along with other small, obscured peaks that are
probably due to the minor stereoisomer of 16. Clearly 14
ismore reactive toward DMDO than is 11.
ported by grant no. 1R15ESOD0880901 from the
National Institute of Health.
References and notes
In summary, we report the first unambiguous observa-
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stable, well-known isomer. The direct observation of the
oxepin-2,3-oxide 12 and its conversion into the stable
product 14 suggests that incubation of 11 with liver
microsomal extract might provide 14 asan ioslable
product. The surprising finding that 12 decomposes
below +10 °C despite having an activation barrier for
concerted ring opening calculated to be 10 kcal/mol
higher than that for 1, suggests that this molecule has
found a lower-energy rearrangement pathway. One
possibility might be spontaneous heterolysis in the
(albeit) moderately polar acetone solution to a minute
quantity of 17, a resonance stabilized, possibly homo-
aromatic, intermediate that rapidly rearrangesto 13 and
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around 0 °C,5 isconcerted since the analogouszwitter-
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5
amountsof acid suggests that its protonated form (18)
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HO
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(16)
17
18
CHO
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Acknowledgements
The authorsthank ProfessorsJoel F. Liebman (UMBC)
and Richard P. Johnson (UNH) for helpful discussions
and Ms. Kathy Gallagher (UNH) for running the low-
temperature NMR spectra described in this paper. The
support of Dr. Dhananjaya by the UNH Provost’s office
is acknowledged. Early stages of this work were sup-
18. Corresponding NMR spectrum predicted using Chem-
NMR (ChemOffice, thanksto Cambridge Software for
donation of thispackage): d 4.12 (d, 1H); d 4.92 (d, 1H); d
5.69 (d, 1H); d 6.56 (d, 1H); d 7.07–7.23 (m, 4H).
19. Dowd, P.; Hershine, R.; Ham, S. W.; Naganathan, S.
Science 1995, 269, 1684–1691.