Does electrophilic activation of nitroalkanes in polyphosphoric acid involve formation of nitrile oxides?

The mechanistic rationale involving activation of nitroalkanes towards interaction with nucleophilic reagents in the presence of polyphosphoric acid (PPA) was re-evaluated. Could nitrile oxide moieties be formed during this process? This experiment demonstrates that at least in some cases this could happen, as generated nitrile oxides were successfully intercepted as adducts of [3 + 2] cycloadditions.

Preparation of spiro[indole-3,5'-isoxazoles] via Grignard conjugate addition/spirocyclization sequence.

A highly efficient one-pot procedure combining conjugate addition of Grignard reagents to (2-nitroalkenyl)indoles and sub-sequent Brønsted acid-assisted spirocyclization allowed for preparation of 4'H-spiro[indole-3,5'-isoxazoles] in a diastereomerically selective fashion. Utilization of alkyl Grignard reagents provided an easy access to 4'-alkylsubstituted derivatives hardly available by other means.

Preparation of 3,5-diarylsubstituted 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones via base-assisted cyclization of 3-cyanoketones.

A convenient preparative method is developed allowing for expeditious assembly of 3,5-diarylsubstituted 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones from routinely available inexpensive synthetic precursors. These compounds could not be prepared via the previously known protocols, as 2-aminofuran derivatives were produced instead.

Synthesis of 2-(1H-Indol-2-yl)acetamides via Brønsted Acid-Assisted Cyclization Cascade.

An efficient and straightforward Brønsted-acid mediated cascade process was developed, involving cyclization of readily available ß-ketonitriles into 2-aminofurans, and their subsequent recyclization into 2-(1H-indol-2-yl)acetamides is developed. This synthetic route opens a new avenue for an expeditious assembly of various isotryptamine derivatives for medicinal chemistry.