Copper-catalyzed
cycloisomerization of 3-iminocyclopropenes for
synthesis of pyrroles has been developed. The reaction allows regioselective
construction of pyrroles with various substitution patterns, including
fully substituted pyrroles. The method was successfully applied to
synthesis of steroidal pyrroles as well as a N-fused pyrrole.
A Brønsted
acid-mediated synthesis of pyrazoles from conjugated
hydrazones through a β-protonation/nucleophilic addition/cyclization/aromatization
sequence was developed. This protocol utilizing the ambiphilic reactivity
of hydrazones enables not only self-condensation but also cross-condensation,
affording multisubstituted pyrazoles in high yields, with a broad
substrate scope. This sequential reaction proceeds under mild conditions
via a simple operation. Moreover, the method can be applied to the
synthesis of a nonsteroidal anti-inflammatory drug, Lonazolac.
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