Yield:1383675-85-1 62.2%

Reaction Conditions:

with N-iodo-succinimide in acetonitrile at 17 - 25; for 1 h;

Steps:

8 Preparation of 3-iodo-6,7-dihydro-5H-pyrazolo[5,1-b][1,3]oxazine

To a solution of 6,7-dihydro-5H-pyrazolo[5,1-b][1,3]oxazine (83.0 g, 669.3 mmol) in CH₃CN (1500 mL) was added N-iodosuccinimide (155.0 g, 688.8 mmol). The mixture was stirred at r.t. for 1 h before being slowly poured into vigorously stirred water (1000 mL). Saturated aqueous sodium thiosulphate (500 mL) was added, and the resulting mixture was extracted with ethyl acetate (2×800 mL). The combined organic layers were washed with water, dried over Na₂SO₄, and concentrated under reduced pressure. The resulting residue was purified by column chromatography on silica gel (petroleum ether: EtOAc=1:1) to give 3-iodo-6,7-dihydro-5H-pyrazolo[5,1-b][1,3]oxazine (105.0 g, 62.2%) as a yellow solid. ¹H NMR (300 MHz, DMSO-d₆, 30° C.) 2.19-2.12 (2H, m), 4.10-3.98 (2H, m), 4.34-4.31 (2H, m), 7.28 (1H, m). m/z: ES+[M+H]+ 251.

References:

US2016/376287,2016,A1 Location in patent:Paragraph 0638