A new synthetic method for the preparation of cyclic malonic acid monoesters in aqueous media was developed based on the combination of a metathesis reaction and subsequent biocatalytic hydrolysis with a pig liver esterase in a one-pot synthesis. Both reaction steps proceed smoothly under optimized conditions in aqueous media requiring only a low amount of the metal catalyst for the metathesis reaction. Notably, the applied biocatalyst turned out to be highly compatible with the metal catalyst showing no significant influence on the enzyme activity.
Supramolecular, water-soluble additives based on calix[n]arenes exhibit a beneficial influence on the ring-closing and cross metathesis of non-polar substrates in pure aqueous medium using standard Grubbs-II and Hoveyda-II catalysts. The catalytic activity observed in water is virtually the same as that in pure methanol. Quantitative yields of metathesis product can be achieved under mild aerobic conditions in/on water by (micro)solubilization of both the catalyst and starting materials by the macrocycles.
A range of water-immiscible commercially available Grubbs-type precatalysts can be used in ring-closing olefin metathesis reaction in high yields. The synthetic transformation is possible in pure water under ambient conditions. Sulfocalixarenes can help to boost the reactivity of the metathesis reaction by catalyst activation, improved mass transfer, and solubility of reactants in the aqueous reaction media. Additionally, the use of supramolecular additives allows lower catalyst loadings, but still high activity in pure water under aerobic conditions.
Vorteile von Wasser als Lösungsmittel liegen auf der Hand: Es ist ungiftig und nicht brennbar, während organische Lösungsmittel oft giftig, teuer und leicht entflammbar sind und noch dazu aus Kohlenstoffquellen gewonnen werden müssen [8,9] [3].Es ist somit nicht verwunderlich, dass diese -zumindest in Industriestaaten -gut verfügbare, billige und in guter Reinheit zu erhaltene Verbindung auch als Lösungs-mittel in chemischen Prozessen eingesetzt wird. Gerade in den letzten Jahren ist das Interesse am Lösungsmittel Wasser und insbesondere an Synthesen "in water" [4], "on water" [5] oder "in the presence of water" signifikant gestiegen, wobei auf diese Detailunterschiede im Rahmen dieser Zusammenstellung nicht näher eingegangen werden soll [6,7].
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