Organic Letters
Letter
forming an isomeric hydroxy epoxide which, in turn, hydrolytically
opens in an anti-fashion to yield trans−cis triol 9. While feasible, the
formation of the isomeric epoxide does not offer rationale for
stereochemistry of oxazoline-2-thione 8. We therefore prefer the SN1
mechanism with the iminium ion as an intermediate for both 8 and 9.
(11) We were unable to isolate intermediates A or C shown in
Scheme 6: in the absence of sodium azide epoxide 10 is stable with
TFA, plausibly indicating that the first step in the rearrangement
requires nucleophilic catalysis. In the presence of NaN3 the Schmidt
rearrangement occurs faster than the first step, preventing isolation of
A (or C).
diketopiperazinoquinolinols containing reactive oxirane, fused
to quinolinol, and spiro-connected to the diketopiperazine
moiety. Several examples of subsequent transformations
presented in this paper attest to the synthetic utility of primary
photoproducts 2 as versatile synthons for rapid access to novel
polyheterocyclic molecular architectures. The modular assem-
bly of photoprecursors from simple building blocks via well-
established coupling reactions gives additional advantage to this
photoassisted synthetic methodology, especially in the context
of diversity-oriented synthesis.
ASSOCIATED CONTENT
* Supporting Information
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S
Experimental details and NMR spectra. This material is
AUTHOR INFORMATION
Corresponding Author
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Support of this research by the NSF (CHE-1362959) is
gratefully acknowledged.
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REFERENCES
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(10) An alternative explanation for the stereochemistry of triol 9
involves intramolecular epoxide ring opening by the benzylic OH
441
Org. Lett. 2015, 17, 438−441