Dirhodium Caprolactamate Catalyzed Alkoxyalkylation of Terminal Alkynes

Abstract

Dirhodium caprolactamate [Rh₂(cap)₄] effectively catalyzes alkoxyalkylation of terminal alkynes in the presence of tert-butyl hydroperoxide (TBHP) under mild conditions.

Key words

alkoxyalkylation - alkynes - catalysis - dirhodium(II)

• References and Notes


For Rh₂(cap)₄-catalyzed allylic oxidation, see:
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• 11 General Experimental Procedure for the Preparation of 2-Vinyl Ethers Alkyne (0.50 mmol) and Rh₂(cap)₄·2MeCN (0.0025 mmol, 1.8 mg, 0.5 mol%) were mixed in Et₂O (10 mL), and TBHP (5–6 M in decane, 1.0 mmol) was added. After stirring at 50 °C for the indicated time (Table 2), the reaction mixture was evaporated to give the crude product, which was purified by silica gel column chromatography using EtOAc–PE as eluent to obtain 2-vinyl ethers. This General Experimental Procedure was carried out using 1a (51 mg, 0.50 mmol) and 2f (10 mL). The reaction mixture was stirred for 14 h at 50 °C and purified by silica gel chromatography using PE–EtOAc (10:1) as eluent to give products (E)-3m and (Z)-3m. Compound (E)-3m: colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.42 (d, J = 7.6 Hz, 2 H), 7.34 (t, J = 7.6 Hz, 2 H), 7.28 (s, 1 H), 6.65 (d, J = 16.0 Hz, 1 H), 6.11 (dd, J = 16.0, 7.6 Hz, 1 H), 4.02–3.90 (m, 1 H), 3.56–3.48 (m, 2 H), 3.42 (s, 3 H), 3.40 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 136.6, 133.8, 128.8, 128.1, 126.82, 126.80, 81.6, 75.9, 59.5, 56.9. ESI-HRMS: m/z calcd for C₁₂H₁₆NaO₂ [M + Na]⁺: 215.1043; found: 215.1042. Compound (Z)-3m: colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.40–7.28 (m, 5 H), 6.78 (d, J = 11.6 Hz, 1 H), 5.58 (dd, J = 11.6, 9.6 Hz, 1 H), 4.46–4.37 (m, 1 H), 3.57–3.51 (m, 2 H), 3.43 (s, 3 H), 3.27 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 136.8, 134.2, 130.0, 128.9, 128.6, 127.6, 76.2, 75.5, 59.6, 56.6. ESI-HRMS: m/z calcd for C₁₂H₁₆NaO₂ [M + Na]⁺: 215.1043; found: 215.1044. See the Supporting Information for experimental details and characterization data for all new compounds.
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