ORGANIC
LETTERS
2001
Vol. 3, No. 23
3647-3650
New Heterocyclic Precursors for
Thermal Generation of Reactive,
Electron-Rich 1,2-Diaza-1,3-butadienes
Robert K. Boeckman, Jr.,* Ping Ge, and Jessica E. Reed
Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627-0216
Received August 11, 2001
ABSTRACT
The preparation and thermolysis of new stable heterocyclic precursors of 1,2-diaza-1,3-butadienes is described. The resulting reactive diazadienes
are trapped in situ with N-phenyldiazamaleimide. The effect of precursor structure on the temperature at which the diazadienes are generated
is discussed.
The chemistry of 1,2-diaza-1,3-butadienes 1, or azoalkenes
as these substances are also known, has been under active
investigation for a number of years.1 The reactivity of these
intermediates, either isolated or generated in situ, has been
shown to include the addition of a variety of nucleophiles.2
Azadienes 1 also undergo ready cycloaddition with a
structurally diverse group of electron-rich and electron-
deficient olefins, as well as 1,3-dipoles, and afford as
products a variety of heterocyclic ring systems.3
The usual methods of synthesis of azadienes such as 1
involve either (1) based-induced dehydrohalogenation of
R-halohydrazones obtained either by halogenation of hydra-
zones or conversion of R-halo carbonyl derivatives to the
hydrazones4 or (2) oxidation of hydrazones with various
oxidizing agents such as I2 or HgO.5 While conjugated,
electron-deficient examples of 1 (R1 ) EWG or Ar or R2 )
alkyl, Ar, or EWG) have been prepared (often in low yield
and purity), those cases bearing as R2 small alkyl or electron
donor groups tend to undergo ready dimerization unless
intercepted by an appropriate coreactant (Figure 1).6 Thus,
the aforementioned synthetic methods become problematic
in these latter cases, since the azadienes must often be
generated in the presence of nucleophilic bases or solvents.
Byproducts from their generation can be difficult to remove
which can compromise subsequent transformations.
In connection with our interest in developing environ-
mentally benign methods for preparation of heterocyclic
(1) (a) Attanasi, O. A.; Filippone, P. Synlett 1997, 1128-1140. (b)
Gilchrist, T. L.; Rocha Gonsalves, A. M. d. A.; Pinho e Melo, T. M. V. D.
Pure Appl. Chem. 1996, 68, 859-862. (c) Attanasi, O. A.; Filippone, P.
Top. Heterocycl. Syst.: Synth., React. Prop. 1996, 1, 157-167. (d) Attanasi,
O. A.; Caglioti, L. Org. Prep. Proced. Int. 1986, 18, 299-327.
(2) (a) Arcadi, A.; Attanasi, O. A.; De Crescentini, L.; Rossi, E.; Serra-
Zanetti, F. Synthesis 1996, 533-6. (b) Arcadi, A.; Attanasi, O. A.; Liao,
Z.; Serra-Zanetti, F. Synthesis 1994, 605-8. (c) Schantl, J. G.; Karpellus,
P.; Prean, M. Tetrahedron 1982, 38, 2643-52.
(3) (a) Gilchrist, T. L.; Sanchez Romero, O. A.; Wasson, R. C. J. Chem.
Soc., Perkin Trans. 1 1989, 353-9. (b) Sommer, S. Angew. Chem. 1979,
91, 756-7. (c) Sommer, S. Chem. Lett. 1977, 583-6. (d) Zelenin, K. N.;
Nikitin, V. A.; Anodina, N. M. Khim. Geterotsikl. Soedin. 1973, 124-8.
(4) (a) Gilchrist, T. L.; Sanchez Romero, O. A.; Wasson, R. C. J. Chem.
Soc., Perkin Trans. 1 1989, 353-9. (b) Attanasi, O. A.; Grossi, M.; Mei,
A.; Serra-Zanetti, F. Org. Prep. Proced. Int. 1988, 20, 408-14. (c) Attanasi,
O.; Filippone, P.; Mei, A.; Serra-Zanetti, F. J. Heterocycl. Chem. 1985,
22, 1341-3.
(5) (a) Schantl, J. Tetrahedron Lett. 1971, 153-6. (b) Schantl, J. Monatsh.
Chem. 1972, 103, 1705-17. (c) Schantl, J. Monatsh. Chem. 1972, 103,
1718-29.
(6) (a) Schantl, J. Monatsh. Chem. 1974, 105, 220-8. (b) Schantl, J.
Monatsh. Chem. 1974, 105, 314-21. (c) Schantl, J. Monatsh. Chem. 1974,
105, 322-6.
10.1021/ol0165645 CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/17/2001