Ruthenium catalysts for olefin metathesis are widely viewed as water-tolerant. Evidence
is presented, however, that even low concentrations of water cause catalyst
decomposition, severely degrading yields. Of 11 catalysts studied, fast-initiating
examples (e.g., the Grela catalyst
RuCl
2
(H
2
IMes)(=CHC
6
H
4
-2-O
i
Pr-5-NO
2
)
were most affected. Maximum water tolerance was exhibited by slowly initiating iodide
and cyclic (alkyl)(amino)carbene (CAAC) derivatives. Computational investigations
indicated that hydrogen bonding of water to substrate can also play a role, by retarding
cyclization relative to decomposition. These results have important implications for
olefin metathesis in organic media, where water is a ubiquitous contaminant, and for
aqueous metathesis, which currently requires superstoichiometric
“catalyst” for demanding reactions.
The regioselective iodination of different 2-mono-, 3-mono-and 2,3-disubstituted 6-aminoquinoxalines, which takes place at their 5-position, was rationalized on the basis of Hückel theory calculations. Oxazolo-and thiazolo [5,4-f]quinoxaline analogues of reported disease-related protein kinases inhibitors were synthesized from the obtained 6-amino-5-iodoquinoxalines by using as key step copper-catalyzed azole ring formation. Pyrazino[b,e]isatins were obtained, for the first time, from the same substrates by recourse to Sonogashira coupling, alkyne hydration, and oxidative cyclization. The absorption and emission properties of the most promising compounds were recorded. In addition, most of the synthesized polycycles were evaluated as protein kinase inhibitors and for their antiproliferative activity towards cancer cells.
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