A straightforward method for ring opening of donor–acceptor
cyclopropanes with trimethylsilyl cyanide as a surrogate of cyanide
ion in the presence of B(C6F5)3 or
trifluoromethanesulfonic acid as a catalyst has been developed. The
methodology provides a short route to γ-cyanoesters that can
be useful synthetic intermediates for the synthesis of diverse bioactive
molecules such as glutaric and δ-aminovaleric acid derivatives,
3-arylpiperidines, or other substituted phenethylamines. Oppositely,
the attempts to synthesize these γ-cyanoesters by direct reaction
of cyclopropanes with sodium cyanide under typical SN2
conditions led to the formation of 2-arylsuccinonitriles.
A simple approach to synthesize 4b,5,6,9-tetrahydro-7H-dibenzo[c,e]pyrrolo[1,2-a]azepin- 7-one has been developed, based on a three-step transformation of 2-(2-bromophenyl)cyclopropane-1,1-diester. The key stage in this method is an intramolecular cross-coupling of 1-(2-bromobenzyl)-5-(2-bromophenyl)pyrrolidin-2-one under continuous flow conditions in an H-Сube-Pro using commercially available supported Pd catalysts.
We report a procedure for the multigram synthesis of 4‐(dimethylamino)pyridinium azide, a stable, non‐explosive, low‐hygroscopic source of azide ion soluble in both protic and aprotic organic solvents. In protic ionic liquid media this reagent was shown to serve as a safer equivalent of toxic and unstable hydrazoic acid. The synthetic utility of this system was demonstrated using donor‐acceptor cyclopropane ring opening as a model process. General procedures furnishing a variety of dialkyl (2‐azido‐2‐arylethyl)malonates or 4‐azido‐4‐arylbutyrates, depending on the protic ionic liquid applied, were elaborated. The conversion times for studied donor‐acceptor cyclopropanes were established providing the relative reactivity sequence. The application of 4‐(dimethylamino)pyridinium azide for a conventional nucleophilic substitution, oxirane ring opening, (3+2)‐cycloaddition to (thio)cyano group as well as their combinations realized as telescopic synthesis was also demonstrated.
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