Pyrazolidine dihydrochloride → 3-(2-methylsulfanyl-pyrimidin-4-yl)-2-o-tolyloxy-6,7-dihydro-5H-pyrazolo[1,2-a]pyrazol-1-one

To a solution of pyrazolidine-bishydrochloride (1.7 g, 11.6 mmol) in pyridine (30 mL) was added 3-(2-Methylsulfanyl-pyrimidin-4-yl)-3-oxo-2-ortho-tolyloxy-propionic acid methyl ester, 1, (2.0 g, 5.78 mmol). The reaction mixture is heated to 110° C. for 18 h. The solvent is removed in vacuo and the resulting residue is purified by silica gel chromatography (10% MeOH/EtOAc, followed by 20% MeOH/EtOAc) to afford 220 mg (10%) of the desired product as a yellow solid. 1H NMR (300 MHz, CDCl3) δ 8.56 (d, J=5.4 Hz, 1H), 7.57 (d, J=5.4 Hz, 1H), 7.23 (d, J=7.5 Hz, 1H), 7.10 (dd, J=7.5, 7.5 Hz, 1H), 6.96 (dd, J=7.5, 7.5 Hz, 1H), 6.82 (d, J=7.5 Hz, 1H), 4.22 (t, J=6.6 Hz, 2H), 4.05 (t, J=6.9 Hz, 2H), 2.72 (dddd, J=6.9, 6.9, 6.9, 6.9 Hz, 2H), 2.62 (s, 3H), 2.48 (s, 3H); ESI+ MS: m/z (rel intensity) 355.0 (100, M++H).