a
RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
› InstitutsangabenThis research was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Scientific Research (B) No. 22H02125 to S.A., and KAKENHI Grant-in-Aid for Transformative Research Areas (Digi-TOS) No. 22H05384 (L.I.).
A low-valent molybdenum species generated by the reduction of a molybdenum precursor with phenylmagnesium bromide catalytically cleaves a C–Cl or C–F bond in an aromatic ketone under mild conditions, followed by cyclization to produce a hydroxyphthalan (1,3-dihydro-2-benzofuran-1-ol) derivative.
15 CCDC 2270774 contains the supplementary crystallographic data for compound 2a. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures
For examples, see:
16a
Cahiez G,
Luart D,
Lecomte F.
Org. Lett. 2004; 6: 4395
17Hydroxyphthalans 2a–e; General Procedure
MoO2Cl2(dtbpy) (4.6 mg, 0.010 mmol, 2 mol%) and the appropriate 2-halobenzophenone 1 (0.50 mmol) were added to a dry Schlenk tube equipped with a Teflon-coated magnetic stirrer bar under a N2 atmosphere. The reaction vessel was fitted with a rubber septum and charged with THF (0.50 mL) from a syringe. The mixture was stirred until a clear light-pinkish solution formed, then cooled to 0 °C (ice bath). Next, a 0.81 mol/L solution of PhMgBr in THF (0.74 mL, 1.2 equiv) was added dropwise by using a syringe pump (addition rate: 0.5 mL/min) at 0 °C under nitrogen. Upon addition, the color of the reaction mixture turned deep violet. After completion of the addition, the septum was removed, the Schlenk tube was sealed under N2 with a screw cap, and the mixture was stirred at rt for 16 h. Tridecane, as an internal standard for GC, and THF (~0.5 mL) were added, and the resulting mixture was stirred vigorously for 5 min. The reaction was then quenched by the addition of a sat. aq NH4Cl (~1 mL) and 30% aq potassium sodium tartrate (~1 mL) with continuous stirring for 5 min. An aliquot was taken directly from the upper organic layer and passed through a plug of Florisil with EtOAc. The resulting solution was analyzed by GC to determine the yield. The aliquot for GC measurement was then returned to the reaction mixture, which was extracted with EtOAc. The combined organic phase was passed through a plug of Florisil, dried (Na2SO4), and then concentrated under reduced pressure. The resulting mixture was analyzed by 1H or 19F NMR to estimate the yield. The product was finally isolated by column chromatography on neutral alumina.
3-(2-Chlorophenyl)-1,3-diphenyl-1,3-dihydro-2-benzofuran-1-ol (2a)
Two batches were prepared in by the general procedure from 1a [213.6 mg, (0.98 mmol) and 211.6 mg (0.97 mmol)]. During workup, the two batches were combined, and the yield (89%) was determined by GC analysis. Purification by column chromatography (neutral alumina; 10% EtOAc–hexane) gave a colorless solid; yield: 323.9 mg (83%, 0.81 mmol). Minor impurities were removed by further purification by GPC (CHCl3). The diastereoselectivity of the product was 1.1:1.
1H NMR (500 MHz, CDCl3): δ = 7.65–7.59 (m, 3 H), 7.55 (dt, J = 7.7, 0.8 Hz, 1 H), 7.53–7.49 (m, 2 H), 7.48–7.27 (m, 27 H), 7.24–7.22 (m, 3 H), 7.15 (td, J = 7.6, 1.3 Hz, 1 H), 3.52 (s, 1 H), 3.07 (s, 1 H). 13C{1 H} NMR (126 MHz, CDCl3): δ = 145.7, 143.8, 143.5, 143.0, 142.85, 142.80, 142.5, 142.3, 142.0, 140.64, 134.9, 133.9, 132.2, 132.1, 129.7, 129.5, 129.4, 129.27, 129.25, 129.0, 128.9, 128.6, 128.5, 128.4, 128.35, 128.31, 127.4, 127.2, 126.6, 126.5, 126.3, 126.08, 126.04, 125.7, 125.0, 124.7, 123.78, 123.66, 108.5, 107.8, 93.90, 92.6. HRMS (APCI+): m/z [M – OH]+ calcd for C26H18ClO: 381.1041; found: 381.1020.
