The use of enaminones and enamines as effective synthons for MSA-catalyzed regioselective synthesis of 1,3,4-tri- and 1,3,4,5-tetrasubstituted pyrazoles
In the present work, an efficient regioselectivesynthesis of 1,3,4-tri- and 1,3,4,5-tetrasubstituted pyrazoles via a methanesulfonic acid (MSA)-catalyzed reaction of hydrazones with enaminones or enamines is reported. Mechanistically, the formation of the title compounds involves the [2+3] cycloaddition of hydrazones with enaminones or enamines followed by aromatization with acid and oxygen. This
An efficient synthetic route to construct ortho-substituted 1-phenyl-1H-pyrazole-4carboxaldehydes and the correspondingethanones starting from 1-phenyl-1H-pyrazol-3-ol is described. Carbon-carbon bond-forming Pd-catalysedcross-couplingreactions were applied for the functionalisation of the intermediate pyrazole triflates. Detailed NMR spectroscopic investigations were undertaken with all obtained
yrimidine (5a) led to 4-benzoyl-3-methyl-1-phenylpyrazole (11) via the initial formation of phenylhydrazones of pyrimidines 4a and 5a. However, 5-benzoyl-4-methyl-2-phenylpyrimidine (4b) and 5-acetyl-2,4-diphenylpyrimidine (5b) reacted with phenylhydrazine to afford, each of them, a mixture of two isomeric pyrazoles. The mechanism of these ring contraction reactions is discussed.
A copper-promoted aerobic oxidative [3+2] cycloaddition reaction for the synthesis of various substituted pyrazoles from N,N-disubstituted hydrazines with alkynoates in the presence of bases is developed. This work involves a direct C(sp3)–H functionalization and the formation of new C–C/C–N bonds. In this strategy, inexpensive and easily available Cu2O serves as the promoter and air acts as the green