This work was supported by JSPS KAKENHI Grants Nos. JP21H05213 (Digi-TOS) (to J.Y.) and JP20K15290 (to E.O.), the Sumitomo Foundation (to E.O.), the Satomi Foundation (to E.O.), and Daiichi Kigenso Kagaku Kogyo (to E.O.). This work was also partly supported by JST ERATO Grant No. JPMJER1901 (to J.Y.).
Oxetanes are frequently utilized in organic synthesis, both as target products and as fairly reactive intermediates. Whereas ring cleavage of oxetanes through polar mechanisms has been extensively investigated, their radical-based counterparts remain underexplored. We used zirconocene and photoredox catalysis to open an oxetane ring in a radical manner. In our protocol, the reaction selectively delivers the more-substituted alcohols via putative less-stable radicals. This method not only affords the corresponding hydrogenated products, but also provides unique benzylidene acetal products.
3 For another recent example of the construction of an oxetane ring, see:
Qi D,
Bai J,
Zhang H,
Li B,
Song Z,
Ma N,
Guo L,
Song L,
Xia W.
Green Chem. 2022; 24: 5046
162-Hydroxybutyl Benzoate (2A); Typical Procedure
1,4-CHD (58.6 μL, 0.60 mmol, 3.0 equiv) and oxetane 1A (0.20 mmol, 1.0 equiv) were added to a solution of Ir(4-MeOppy)3 (4.5 mg, 6.0 μmol, 3.0 mol%), Cp2Zr(OTf)2·THF (5.9 mg, 10 μmol, 5.0 mol%), and TU1 (20.0 mg, 120 μmol, 60 mol%) in THF (2.0 mL), and the resulting mixture was irradiated with a 456 nm LED (Kessil) for 12 h. The mixture was then passed through a short silica gel pad with EtOAc as an eluent, and the filtrate was concentrated in vacuo. The residue was purified by preparative TLC (hexane/EtOAc = 2:1, then CHCl3/acetone = 9:1) to afford a colorless oil [Run 1; yield: 32.0 mg (84%), Run 2; yield: 24.4 mg (65%)]. 1H NMR (400 MHz, CDCl3): δ = 8.08–8.04 (m, 2 H), 7.60–7.55 (m, 1 H), 7.48–7.43 (m, 2 H), 4.41 (dd, J = 11.6, 3.2 Hz, 1 H), 4.25 (dd, J = 11.6, 6.4 Hz, 1 H), 3.96–3.89 (m, 1 H), 2.08 (d, J = 4.8 Hz, 1 H), 1.68–1.56 (m, 2 H), 1.04 (t, J = 7.2 Hz, 3 H). 13C NMR (101 MHz, CDCl3): δ = 166.7, 133.1, 129.9, 129.6, 128.4, 71.4, 68.8, 26.4, 9.8. The spectra were in accordance with those reported in the literature.17
17
Iwasaki F,
Maki T,
Onomura O,
Nakashima W,
Matsumura Y.
J. Org. Chem. 2000; 65: 996
