Abstract
Friedel–Crafts alkylation of indole and its derivatives with a variety of electron-deficient
alkenes catalyzed by Mg and Ca salts has been studied. The dependence of the results
on the nature of the starting olefins, substituents on indole, and Michael acceptors,
as well as on the composition of the Lewis acid is discussed. High yields of the addition
products were achieved in the addition of indole to β,γ-unsaturated α-keto esters
and coumarin derivatives, some nitroolefins, and arylidenemalonates. Reactions involving
arylidenemalonates were found to be the most versatile and smooth, the best yields
reached 92%. Among the Mg and Ca salts tested, magnesium iodide (MgI2) proved to be the most appropriate catalyst in the addition to various unsaturated
carbonyl compounds, while calcium triflimide [Ca(NTf2)2] efficiently catalyzed the addition to nitroolefins.
Key words
Friedel–Crafts reaction - Lewis acid catalysis - indole - Michael addition - alkenes
