Catalyst Efficacy of Homogeneous and Heterogeneous Palladium Catalysts in the Direct Arylation of Common Heterocycles

Abstract

The direct arylation of several common heterocycles, using homogeneous and heterogeneous palladium (pre)catalysts, has been examined by initial rate analysis. The study reveals that apparently distinct palladium catalysts can display similar activities in such transformations, implying formation of a comparable active palladium catalyst phase. A substrate dependence was noted for the palladium catalysts examined.

Key words

catalysis - palladium - homogeneous - heterogeneous - arylation - heterocycles

• References and Notes

• 1 Leibniz Institute for Catalysis, Albert-Einstein-Str. 29a, 18059 Rostock, Germany. Email: [e-mail]
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Other supported PdNPs are available for direct arylation, e.g. Pd@PPy, which are highly active and appear to operate as molecular/colloidal Pd species at higher reactions temperatures (150 °C), see:
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; also see ref. 9a High turnover numbers can be achieved in direct arylations using Pd(OAc)₂ at higher reaction temperatures, see:
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• 16 4-n-Butyl-2-phenylthiophene (6) ¹H NMR (400 MHz, CDCl₃): δ = 7.61–7.56 (m, 2 H), 7.42–7.36 (m, 2 H), 7.31–7.25 (m, 1 H), 7.24 (d, J = 1.5 Hz, 1 H), 7.09 (dt, J = 1.5, 1.0 Hz, 1 H), 2.87 (t, J = 7.5 Hz, 2 H), 1.77–1.67 (m, 2 H), 1.50–1.38 (m, 2 H), 0.97 (t, J = 7.5 Hz, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 146.8, 141.9, 136.4, 128.8, 127.0, 126.4, 123.5, 117.9, 33.9, 30.0, 22.4, 14.0. ESI-MS: m/z (ion) = 217 [C₁₄H₁₇S]⁺; ESI-HRMS m/z calcd for C₁₄H₁₇S: 217.1045; found: 217.1024 [C₁₄H₁₇S]⁺.
• 17 5-n-Butyl-2-phenylfuran (8) ¹H NMR (400 MHz, CDCl₃): δ = 7.68–7.63 (m, 2 H), 7.40–7.34 (m, 2 H), 7.23 (tt, J = 7.5, 1.0 Hz, 1 H), 6.56 (d, J = 3.0 Hz, 1 H), 6.08 (dt, J = 3.0, 1.0 Hz, 1 H), 2.70 (app t, J = 7.5 Hz, 2 H), 1.70 (tt, J = 7.5, 6.5 Hz, 2 H), 1.44 (app sext, J = 7.5 Hz, 2 H), 0.97 (t, J = 7.5 Hz, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 156.6, 152.2, 131.4, 128.7, 126.8, 123.4, 107.0, 105.8, 30.4, 28.0, 22.4, 14.0. GC–MS (EI): m/z (ion) = 200 [C₁₄H₁₆O]⁺. HRMS (EI): m/z calcd for C₁₄H₁₆O: 200.1201; found: 200.1202 [C₁₄H₁₆O]⁺.
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