Hypervalent iodine oxidation of 5-substituted and 4,5-disubstituted pyrazol-3(2H)-ones: A facile synthesis of methyl-2-alkynoates and methyl 2,3-alkadienoates
Hypervalentiodineoxidation of various 5-substitutedpyrazol-3(2H)-ones (1a-h) with iodobenzene diacetate or iodosobenzene in methanol results in fragmentative loss of molecular dinitrogen to yield methyl 2-alkynoates (2a-h). However, 5-methyl-4-substitutedpyrazol-3(2H)-ones (3a-d) under similar conditions yield methyl 2,3-allenicesters (4a-d). Methyl 2,3-cycloalkadienoates (6a-e) are obtained by