Synlett 2019; 30(13): 1551-1554
DOI: 10.1055/s-0037-1611869
letter
© Georg Thieme Verlag Stuttgart · New York

Copper-Catalyzed Twofold Silylmetalation of Alkynes

Hiroki Yamagishi
,
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan   Email: shimokawa@kuchem.kyoto-u.ac.jp   Email: yori@kuchem.kyoto-u.ac.jp
,
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan   Email: shimokawa@kuchem.kyoto-u.ac.jp   Email: yori@kuchem.kyoto-u.ac.jp
› Author Affiliations
This work was supported by JSPS KAKENHI Grant Numbers JP15H05641, JP16H04109, JP18H04254, JP18H04409, and JP19H00895. H.Y. thanks The Asahi Glass Foundation for financial support.
Further Information

Publication History

Received: 11 May 2019

Accepted after revision: 29 May 2019

Publication Date:
25 June 2019 (eFirst)

Abstract

The first twofold silylmetalation across a C≡C triple bond was achieved. In the presence of a catalytic amount of copper cyanide, diarylacetylenes were converted into 1,2-dimetalated 1,2-disilyl-1,2-diarylethanes on treatment with silylpotassium species generated in situ from disilane and t-BuOK. The dimetalated species were subsequently protonated to yield a series of 1,2-disilyl-1,2-diarylethanes.

Supporting Information

 
  • References and Notes

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  • 4 The reduction in the isolated yield is due to the difficulty in chromatographically separating the product from the t-BuOSiMe2Ph generated during the formation of the silyl potassium species.
  • 5 1,2-Bis[dimethyl(phenyl)silyl]-1,2-diphenylethane (3a); Typical Procedure An oven-dried Schlenk tube was charged with diphenylacetylene (1a; 53.5 mg, 0.300 mmol), CuCN (5.4 mg, 0.060 mmol), and t-BuOK (108 mg, 0.960 mmol). DME (2.0 mL) and 1,1,2,2-tetramethyl-1,2-diphenyldisilane (2, 244 mg, 0.900 mmol) were added sequentially to the mixture, which was then stirred at 25 °C for 1.5 h. H2O (30 mL) was added at 0 °C, and the resulting biphasic solution was extracted with Et2O (3 × 15 mL). The combined organic layer was washed with brine, dried (Na2SO4), and concentrated under reduced pressure. The resulting residue was purified by column chromatography (silica gel, hexane) and then by GPC (CHCl3 eluent) to give a white solid; yield: 89.2 mg (0.198 mmol, 66%) (minor/major = 1:1.2 as an inseparable mixture). 1H NMR (CDCl3): δ = 7.38–7.36 (m, 2 H × 0.55), 7.34–7.30 (m, 8 H × 0.55), 7.22 (ddd, J = 7.2, 7.2, 1.2 Hz, 2 H × 0.45), 7.14–7.11 (m, 6 H × 0.55 + 4 H × 0.45), 7.07–7.01 (m, 6 H × 0.45), 6.98 (dd, J = 7.2, 1.2 Hz, 4 H × 0.45), 6.92 (d, J = 7.2 Hz, 4 H × 0.45), 6.84–6.83 (m, 4 H × 0.55), 2.88 (s, 2 H × 0.45), 2.75 (s, 2 H × 0.55), 0.10 (s, 6 H × 0.55), –0.17 (s, 6 H), –0.22 (s, 6 H × 0.45). 13C NMR (CDCl3): δ = 142.5, 141.6, 138.5, 138.4, 134.1, 134.0, 131.5, 129.5, 128.8, 128.2, 127.7, 127.6, 127.3, 127.0, 125.1, 125.1, 38.5, 36.8, –2.36, –2.42, –3.36, –4.04. HRMS: m/z [M+] calcd for C30H34Si2: 450.2194; found: 450.2197.
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  • 10 Even though a free silylpotassium species seems to function in the reaction, the formation of a silicate species generated from disilane and tert-butoxide cannot be excluded.
  • 11 Ref. 3b reports an example of monosilylcupration by (R3Si)2Cu(CN)Li2 of a C≡C triple bond however, no report of any type of addition of (R3Si)2Cu(CN)K2 is known.
  • 12 In the presence of smaller amounts of disilane (1.0 equiv) and t-BuOK (1.2 equiv), we obtained recovered alkyne 1a (32%) and disilylated product 3a (19%), as well as the monosilylated alkene (25%), after protic workup. This suggests that a monosilylated copper species is formed just before the the silylpotassium species is consumed. The monosilylated copper species might also add to the alkyne to provide the monosilylated alkene eventually.