Activation of Aryl and Vinyl Triflates by Palladium and Electron Transfer – Electrosynthesis of Aromatic and α,β-Unsaturated Carboxylic Acids from Carbon Dioxide

✍ Scribed by Anny Jutand; Serge Négri

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 600 KB
• Volume: 1998
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/(sici)1099-0690(199809)1998:9<1811::aid-ejoc1811>3.0.co;2-v

✦ Synopsis

The electrochemical reduction of aryl and vinyl triflates in presence of an electron source, so that they react with electrophiles such as CO 2 . The reaction proceeds through an the presence of CO 2 and a catalytic amount of palladium results in the formation of aromatic and α,β-unsaturated activation of the C-O bond of the aryl or vinyl triflate by oxidative addition to a palladium(0) complex, followed by an carboxylic acids. Aryl and vinyl triflates usually undergo palladium-catalysed cross-coupling reactions with activation by electron transfer of the thus formed aryl-or vinylpalladium(II) complexes. nucleophiles. Their reactivity has been reversed in the As we have previously reported, [4] aryl triflates, ArOTf, p-MeϪC 6 H 4 Ϫ Ϫ 2.71 Ϫ2.53 are electroactive compounds (Table 1). Their electrochemip-MeOϪC 6 H 4 Ϫ Ϫ 2.67 Ϫ [b] p-tBuϪC 6 H 4 Ϫ Ϫ 2.74 Ϫ2.68 cal reduction leads, after hydrolysis, to a mixture of phenol o-MeϪC 6 H 4 Ϫ Ϫ 2.70 Ϫ2.46 ArϪOH and arene ArϪH, as illustrated in Table 2 (entry 1-naphthylϪ Ϫ 1.95 Ϫ1.89 2-naphthylϪ Ϫ 2.01 Ϫ1.90

1. for 1-naphthyl triflate. When the electrolysis was performed at the controlled potential of Ϫ2.0 V at room tem- [a] Volts vs. SCE; reduction peak potentials were determined at a perature in DMF, 1-naphthol was formed as the major steady gold disc electrode (i.d. 0.5 mm) at a scan rate of 0.2 Vs Ϫ1 compound (86% yield), showing that the cleavage of the in DMF containing nBu 4 NBF 4 (0.3 ) at 20°C. Ϫ [b] No reaction at 20°C.