Title: A pyrazole to furan rearrangement. Thermolysis of 5-azido-4-formylpyrazoles
Authors: Svenstrup, N ×
Simonsen, KB
Thorup, N
Brodersen, J
Dehaen, Wim
Becher, J #
Issue Date: Jan-1999
Publisher: Amer chemical soc
Series Title: Journal of Organic Chemistry vol:64 issue:8 pages:2814-2820
Abstract: 5-Azido-3-benzyl-4-formyl-1-phenylpyrazoles 1a-c extrude dinitrogen upon heating in toluene to give the corresponding nitrenes, which immediately rearrange via a new ring-opening ring-closure reaction to produce an equimolar mixture of 4-cyano-2-phenyl-3-phenylazofurans 2a-c and 3-benzyl-4-cyano-1-phenylpyrazoles 3a-c. The formation of the 4-cyano-2-phenyl-3-phenylazofurans 2a-c is the first example in the pyrazole series of a nitrene rearrangement, in which the parent heterocyclic system of the product differs from that of the starting material. The isolation of equimolar amounts of the two products points to the fact that their formation occurs by two mechanistically interconnected pathways, between which the exchange of a redox equivalent takes place. Evidence for the existence of two mechanistically interlinked pathways is presented, and the insight into the stoechiometry of the reaction is taken advantage of to optimize the reaction with respect to either of the two products 2 or 3. Thus, it is demonstrated how one can bias the two pathways using external reagents, thereby changing the product distribution ratio 2:3 from 1:1 in the unbiased case, to 1:4 in one direction, and to better than 20:1 in the other direction.
ISSN: 0022-3263
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Molecular Design and Synthesis
× corresponding author
# (joint) last author

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