A rapid and efficient method is described for the selective synthesis of enol esters via the microwave-accelerated addition of carboxylic acids to terminal alkynes. The method employs the readily available [RuCl2(p-cymene)(PPh3)] complex as catalyst without the need of bases, and reactions are complete in 20 min.
An efficient and highlyselective synthesis of vinyl esters was developed that employed carboxylic acids and terminalalkynes as reagents, and novel tethered (η1:η6-phosphanoarene)ruthenium complexes as catalyst precursors. With these catalyst systems, the reactions were somewhat slower than when using the best catalysts reported to date, but the selectivities were excellent with up to 98 % of the
开发了一种高效且高选择性的乙烯基酯合成方法,其使用羧酸和末端炔作为试剂,并使用新型系链 (η1:η6-膦芳基) 钌配合物作为催化剂前体。使用这些催化剂体系时,反应比使用迄今为止报道的最佳催化剂时稍慢,但选择性非常好,马尔可夫尼科夫异构体高达 98%。此外,这些催化剂的营业额 (TON) 为 5000,大大优于竞争对手。微量的水对反应速率有有益的影响,同时保持相同的选择性。此外,160 °C 的微波加热也大大加速了反应,尽管会损害选择性。最后,
Catalytic activity assessment of [RuCl2 (p-cymene) (PTA)] in the synthesis of enol esters
作者:Eric Musengimana、Claver Fatakanwa
DOI:10.1007/s13738-015-0732-7
日期:2016.2
The addition of carboxylic acids onto 1-hexyne was catalyzed by [RuCl2 (p-cymene) (PTA)] complex to give enol esters. Accordingly, the Markovnikov addition-type product was selectively obtained. The microwave-assisted reactions at 160 °C confirmed the influence of the temperature, where quantitative to excellent yields were obtained in 30 min. The catalyst loading test proved that [RuCl2 (p-cymene) (PTA)] complex can be efficiently used with a 1/1500 ratio to carboxylic acid providing the TON value of 1500.
The catalytic activity of four ruthenium imidazol(in)ium-2-dithiocarboxylates was evaluated for the synthesis of vinyl esters through addition of 4-acetoxybenzoic acid to 1-hexyne, and compared to those of the parent ruthenium-N-heterocyclic carbene complexes and [RuCl2(p-cymene)(PPh3)] (a standard catalyst). It turned out that ruthenium imidazol(in)ium-2-dithiocarboxylates were poorly active and selective. Quantitative yields, indeed, were obtained only after extended reaction times. However, the catalytic activity could be improved significantly under microwave heating or conventional heating in a sealed tube at 160 degrees C, driving the reaction to completion in less than 4 h of reaction. (C) 2009 Elsevier B. V. All rights reserved.