C O M M U N I C A T I O N S
22. Further heating transforms 36 to 22, suggesting that 36 and 37
undergo interconversion at elevated temperature.
heim Pharmaceuticals for generous financial support. T.S. was
supported in part by a Research Fellowship of the Japan Society
for the Promotion of Science (JSPS) for Young Scientists. We thank
Dr. Michiko Sasaki for carrying out the competition experiment
described in eq 1.
Scheme 4. Evidence for Propargylic Cyano Ene Reaction: Isolation
of Enamine 36
Supporting Information Available: Experimental procedures,
characterization data, and 1H and 13C NMR spectra for all new
compounds. This material is available free of charge via the Internet
References
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the propargylic ene and azadiene Diels-Alder reactions but also
to serve as synthetic equivalents for a variety of substituents on
the pyridine ring. For example, hydration and hydrogenation of
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Supporting Information.
In summary, we have described two formal [2 + 2 + 2]
cycloaddition strategies for the construction of polycyclic pyridine
derivatives that proceed via unusual pericyclic cascade mechanisms
featuring the participation of unactivated cyano groups as enophile
and dienophile cycloaddition partners. Further studies are underway
in our laboratory aimed at developing additional synthetically useful
variants of this [2 + 2 + 2] strategy for the synthesis of pyridines.
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(14) Attempts to trap the intermediate allenylimine with the TMS enol ether
derivative of cyclohexanone and with electron-deficient alkenes and alkynes
were unsuccessful. Reaction with enamines proceeded in low yield.
Acknowledgment. We thank the National Institutes of Health
(GM 28273), Merck Research Laboratories, and Boehringer Ingel-
JA106901U
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