Science of Synthesis

Hopkinson, M. N.; Gouverneur, V., Science of Synthesis Knowledge Updates, (2011) 2, 126.

The combination of gold(I) catalysts and the electrophilic fluorinating reagent Selectfluor is capable of mediating an ever-increasing number of impressive cross-coupling reactions. Among these is the cascade rearrangement–oxidative ester migration of propargyl carboxylates reported by Zhang and co-workers.[‌81‌] Upon treatment with [bis(trifluoro­methylsulfonyl)amido](triphenylphosphine)gold(I) [Au(NTf2)(PPh3); 5 mol%] and Selectfluor (‌43‌; 1.5 equiv) in acetonitrile/water (500:1), the alkyl-substituted propargyl benzoate ‌62‌ (R1 = Pr) is converted into the 1-(benzoyloxy)vinyl ketone ‌63‌ in 83% yield after 10 minutes at 80°C (‌Scheme 25‌). Similarly, the analogous propargyl acetate, pivalate, and 4-­methoxybenzoate react to give the corresponding oxyvinyl ketone products although these substrates are less efficient (46, 68, and 70% yields, respectively). The cascade process is successful with both gold(I) and gold(III) catalysts, with platinum(II) chloride also showing some catalytic activity (40% yield) after an extended reaction time. A range of propargyl benzoates ‌62‌ bearing aryl and alkyl substituents at the alkynyl position can be successfully reacted under these conditions, delivering the corresponding 1-(benzoyloxy)vinyl ketones ‌63‌ in moderate to high yields. By contrast, substrate ‌64‌, with a methyl group at the propargylic position, does not give the cross-coupled product, instead delivering the homocoupling product ‌65‌ in 60% yield (see Section ‌3.6.13.1.3.4‌).

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