3,3′-Bis(arylbenzofurans) via a Gold-Catalyzed Domino Process

Abstract

A new heterogeneous gold-catalyzed system for the domino cyclization oxidative coupling of 2-alkynyl phenols for the formation of 3,3′-bisbenzofurans was developed. The substrate and the catalyst scope as well as the reaction conditions were investigated and optimized. This method provides access to this novel structural theme in two steps starting from commercially available chemicals. The molecular structure of the 3,3′-bisbenzofurans was confirmed by single-crystal X-ray analysis.

Key words

domino process - gold catalysis - 3,3′-bisbenzofurans - dimerization - oxidative coupling

References and Notes

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24

The procedure described for compound 2a was applied for compounds 2b-g. HAuCl₄ (17.5 mg, 10 mol%) was placed into a 20 mL vial (well dried), equipped with a stir bar. Et₂O (10 mL) was added, and the mixture was stirred for 5 min at r.t. Then, 2-alkynlphenol (100 mg, 1 equiv) was added first, followed by PhI(OAc)₂ (848 mg, 5 equiv) 5 min later. The mixture was stirred at r.t. overnight. The reaction mixture was filtered and concentrated. The crude product was purified by flash column chromatography or on preparative TLC. Compound 2a was isolated as a white powder with a yield of 37% (37 mg); mp 179-181 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 7.80-7.74 (m, 4 H), 7.63 (d, J = 8.2 Hz, 2 H), 7.33 (m, 2 H), 7.29-7.20 (m, 6 H), 7.17-7.07 (m, 4 H). ^¹³C NMR (101 MHz, CDCl₃): δ = 154.76 (2 C), 152.37 (2 C), 130.84 (2 C), 129.87 (2 C), 128.98 (4 C), 128.92 (2 C), 126.62 (4 C), 125.32 (2 C), 123.41 (2 C), 121.11 (2 C), 111.62 (2 C), 108.07 (2 C). ESI-HRMS: m/z calcd for [C₂₈H₁₈O₂Na]⁺: 409.1204 [M + Na]⁺; found: 409.1199.
MS (EI): m/z (%) = 386.1 (100) [M⁺], 308.1 (9), 281.1 (7).
IR: ν = 1600, 1588, 1486, 1470, 1454, 1439, 1338, 1288, 1254, 1203, 1109, 1063, 1026, 1008, 920 cm^-¹.

25

Crystallographic data for compounds 2a and 2b have been deposited at the Cambridge Crystallographic Data Center, the respective deposition numbers are 772967 and 772968.