1,3-Dipolar cycloaddition reaction of 3-trifluoromethyl-4-diazopyrazolinones with acetylenedicarboxylates

Refluxing of 3-trifluoromethyl-4-diazopyrazolinones 1 with dimethyl acetylenedicarboxylates 2 in toluene for 48 h afforded trifluoromethyl-substituted pyrazolo [1,5-d][1,2,4]triazin-7-ones, which resulted from the [3+2] dipolar cycloaddition followed by a rearrangement of the initially produced spiro 3H-pyrazole adducts. However, when 1 was heated to 160 °C in dichlorobenzene (o-DCB) for 8 h, it lost nitrogen and reacted with 2 to give 3-trifluoromethyl furo[2,3-c]pyrazoles.