Triphenylphosphine → 3,4-Dihydro-4-methylene-1H-2-benzopyran

Participants

Reaction Conditions

Reaction Steps

1-[(allyloxy)methyl]-2-iodobenzene (23 g, 83.9 mmol) was dissolved in 100 ml of CH3CN and 58 ml of Et3N. The solution was vacuum degassed (3 cycles) followed by the addition of Pd(OAc)2 (0.9 g, 4.2 mmol) and PPh3 (2.2 g, 8.4 mmol). The mixture was heated to 80° C. until HPLC indicated complete reaction. The mixture was cooled to room temperature and diluted with Et2O (200 ml). The mixture was washed with 1N HCl (2×50 ml); NaHCO3 (2×50 ml); brine (1×50 ml); dried over Na2SO4 and concentrated in vacuo to yield 4-methylene-3,4-dihydro-1H-isochromene (Heterocycles 1994, 39, 497) as an oil. HRMS (ESI+) calcd for C10H10O m/z 146.0732 (M+H)+. Found 146.0728. The crude oil was dissolved in 1:1 CH3OH/CH2Cl2 (500 ml) and 5 ml of pyridine added. The mixture was chilled to −78° C. and ozone was bubbled through the mixture for 1 h, at which time TLC indicated complete reaction. The mixture was purged with N2 at −78° C. and treated with Me2S, then allowed to warm to room temperature and stir for 3 h. The reaction was then diluted with CH2Cl2 and washed with H2O and brine. The organic layer was dried over Na2SO4 and concentrated in vacuo to yield 5.1 g of 1H-isochromen-4(3H)-one as a slight yellow oil after flash chromatography (10% EtOAc/Hexanes) Rf=0.25. 1H NMR (400 MHz, CDCl3) δ 8.05 (d, J=7.88 Hz, 1H), 7.59 (m, 1H), 7.43 (appt, J=7.36 Hz, 1H), 7.24 (d, J=7.67 Hz, 1H), 4.91 (s, 2H), 4.39 (s, 2H. Anal calcd for C9H8O2; C, 72.96; H, 5.44; found C, 72.50; H, 5.29. MS (ESI+) for C9H8O2 m/z 148.8 (M+H)+.

Provenance & Evidence