Yield: 45.5%

Reaction Conditions:

with TurboGrignard in tetrahydrofuran at 5; for 2 h;Inert atmosphere;

Steps:

4.2.29. 3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-6,7-dihydro-5H-pyrazolo[5,1-b][1,3]oxazine (43)
Isopropylmagnesium lithium chloride (3.08 mL, 4.00 mmol) was added dropwise to a stirred solution of 3-iodo-6,7-dihydro-5H-pyrazolo[5,1-b][1,3]oxazine (46, 1.0 g, 4.00 mmol) and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1.2 mL, 6.00 mmol) in THF (10 mL) at 5 °C, over a period of 10 min, under nitrogen. The resulting solution was stirred at 5 °C for 2 h and then concentrated in vacuo. The crude product was purified by flash silica chromatography (0-5% MeOH/DCM) to afford a pale yellow oil. Crystallisation from heptane yielded the title compound (43, 0.455 g, 45.5%) as a white solid; δ_H (400 MHz, DMSO): 1.22 (12H, s, 2×Me₂CO), 2.11-2.18 (2H, m, CH₂), 4.05 (2H, t, J 6.2 Hz, CH₂), 4.29-4.32 (2H, m, CH₂), 7.32 (1H, s, Ar); δ_C (101 MHz, DMSO): 21.11, 24.57 (4 CH₃), 43.60, 65.64, 82.32 (2C), 143.54, 156.26, C-B not seen; m/z (ES⁺) 251.47(100, MH⁺); HRMS (ESI): MH⁺, found 251.15598. C₁₂H₂₀BN₂O₃ requires 251.15615.

References:

Bethel, Paul A.;Campbell, Andrew D.;Goldberg, Frederick W.;Kemmitt, Paul D.;Lamont, Gillian M.;Suleman, Abid [Tetrahedron,2012,vol. 68,# 27-28,p. 5434 - 5444] Location in patent:experimental part