This work was supported by the Japan Society for the Promotion of Science (JSPS), KAKENHI (Grant nos. JP19F01033, JP19H00895, JP21H01934), and partly by the Japan Science and Technology Agency (JST), CREST (Grant no. JPMJCR19R4).
The regioselective anti-silyllithiation of propargylic amines is developed to facilitate the efficient synthesis of alkenylsilanes. This reaction generates an alkenyllithium intermediate that is stabilized by the formation of a five-membered cyclic structure through intramolecular coordination of the nitrogen functional group. Upon subsequent treatment with an electrophile, the alkenyllithium intermediate is further functionalized to afford tetrasubstituted allylic amines bearing a β-silicon substituent.
16Regioselective anti-Silyllithiation of Propargylic Amines 1; General Procedure
The synthesis of 3aa is representative. A 20-mL Schlenk tube was charged with tert-butyl (3-phenylprop-2-yn-1-yl)carbamate (1a) (115.5 mg, 0.499 mmol) and toluene (5.0 mL) under a nitrogen atmosphere, and the resulting solution was cooled to –40 °C. To the mixture was added PhMe2SiLi (2a) (1.5 M in THF, 1.2 mL, 1.75 mmol, 3.5 equiv) dropwise. After stirring the mixture for 3 h at –40 °C, saturated aqueous NH4Cl (1.0 mL) was added at 0 °C. The resulting biphasic solution was extracted with EtOAc (3 × 10 mL). The combined organic layer was washed with brine, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (hexane/CH2Cl2 = 1:2) to provide 3aa (148.6 mg, 0.404 mmol, 81%) as a pale yellow solid.
1H NMR (600 MHz, CDCl3): δ = 7.53–7.50 (m, 2 H), 7.40 (br s, 1 H), 7.38–7.34 (m, 3 H), 7.24–7.20 (m, 3 H), 7.15–7.12 (m, 2 H), 4.66 (br s, 1 H), 3.99 (d, J = 6.1 Hz, 2 H), 1.49 (s, 9 H), 0.20 (s, 6 H). 13C NMR (151 MHz, CDCl3): δ = 155.6, 143.6, 139.4, 139.1, 138.6, 133.8, 129.0, 128.6, 127.9, 127.8, 127.2, 79.3, 47.7, 28.5, –1.5. HRMS (APCI-MS, positive): m/z [M – tBu]+ calcd for C18H20NO2Si: 310.1258; found: 310.1269.
19 CCDC 1982977 contains the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures
20
Feng Q,
Wu H,
Li X,
Song L,
Chung LW,
Wu Y.-D,
Sun J.
J. Am. Chem. Soc. 2020; 142: 13867