Vk. Ahluwalia et al., NOVEL SYNTHESIS OF XY-6-METHYL-5,6-DIHYDROPYRANO[2,3-C]PYRAZOL-4-ONES, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 33(8), 1994, pp. 761-763
The Claisen reaction of 4-acetyl-5-methoxypyrazole derivatives (2a-c)
with ethyl acetate in the presence of pulverised sodium afforded xy-6-
methyl-5,6-dihydropyrano[2,3-c]pyrazol-4-ones (4a-c) instead of the ex
pected 1H-pyrano[2.3-c]pyrazol-4-ones (1a-c).