Alexey A. Festa

Marine indole alkaloids containing an 1-(indol-3-yl)ethane-1,2-diamine fragment (Review)

Data on the isolation from natural sources, biological properties, and synthesis of indole alkaloids containing an 1-(indol-3-yl)ethane-1,2-diamine fragment are reviewed.

Novel domino reaction of N-(cyanomethyl)-5,10-dihydro[1]benzosilano[3,2-c]pyridinium salts with salicylaldehydes

The synthesis of benzosilanochromenoimidazopyridines was accomplished by a domino reaction of 5,5-dimethyl-10-oxo- and 10-hydroxy-10-allyldihydrobenzosilanopyridinium N-cyanomethyl salts with salicyl- and 5-bromosalicylaldehydes. It was found that in the case of the 10-allyl-10-hydroxy-dihydrobenzosilanopyridinium salts the reaction occurred at both α-positions of the pyridine fragment to form a mixture of the isomeric benzosilano[3,2-c]- and benzosilano[2,3-d]chromenoimidazo-pyridines.

Synthesis of indoles under the action of visible light (microreview)

This microreview considers the use of visible light and photoredox catalysis for the synthesis of a widely used class of compounds – indoles, covering literature sources starting from 2012. The synthetic approaches are categorized according to their catalytic mechanism.

Synthesis of Chromenoimidazoles, Annulated with an Azaindole Moiety, through a Base-Promoted Domino Reaction of Cyano­methyl Quaternary Salts

The reactivity of N -cyanomethyl quaternary salts of 4-, 5- and 7-azaindoles towards salicylic aldehydes has been studied. The interaction of azaindolium salts with salicylic aldehydes proceeds as a base-promoted domino reaction, giving the corresponding chromenoimidazopyrrolopyridines. In the case of the 7-(cyanomethyl)-7-azaindolium salt, the reaction was found to be more sensitive, but the use of the 1-methyl-substituted salt allowed the synthesis of the desired compounds, incorporating the heterocyclic core of isogranulatimide C, a marine natural product.

Synthesis of pyrazino[1,2-a]indoles and indolo-[1,2-a]quinoxalines (microreview)

The review is dedicated to the methods of synthesis of pyrazino[1,2-a]indoles and indolo[1,2-a]-quinoxalines. The primary approach to the synthesis of these heterocyclic systems is the annulation of a pyrazine ring to a functionalized indole ring by means of condensation of carbonyl compounds, radical reactions catalyzed by transition metals, as well as hypervalent iodine compounds.

Domino reaction of N-(cyanomethyl)-1,3-azolium quaternary salts with o-hydroxybenzaldehydes: scope and limitations

A route towards chromenes, annulated with an imidazo[5,1-c][1,4]thiazine core through a base-promoted domino reaction of thiazolium quaternary salts, has been developed. The synthesised compounds show high cytotoxic activity against human tumour cell lines.

1-Methyl-3-(2-oxo-2H-chromen-3-yl)-1H-imidazol-3-ium picrate

The title salt, C13H11N2O2 +·C6H2N3O7 −, is the unexpected product of a domino reaction of 3-cyanomethyl-1-methylimidazolium chloride with salicylic aldehyde in the presence of picric acid. In the cation, the 1H-imidazole ring is twisted by 63.2 (1)° from the 2H-chromen plane. In the crystal, cations and anions are alternately stacked along the a axis through π–π stacking interactions between the almost parallel aromatic rings [centroid–centroid distances = 3.458 (2) and 3.678 (2) Å]. The stacks are further linked by C—H⋯O hydrogen bonds into a two-tier layer parallel to (001).

DBU-Catalyzed Alkyne–Imidate Cyclization toward 1-Alkoxypyrazino[1,2-a]indole Synthesis

1-(Propargyl)indol-2-carbonitriles react with alcohols to afford 1-alkoxypyrazino[1,2- a]indoles under DBU-catalyzed microwave-assisted conditions. The reaction scope includes a wide range of indoles, primary and secondary alcohols, and a thiol. The initial mechanistic study shows that the domino process presumably proceeds through an alkyne-allene rearrangement, imidate formation, and nucleophilic cyclization reaction sequence.

Revision of the Structure and Total Synthesis of Topsentin C

An efficient synthetic approach to access (indol-3-yl)ethane-1,2-diamines with a protecting group at the indole N atom from readily available 3-(2-nitrovinyl)indoles is reported. This approach includes solvent-free conjugate addition of O -pivaloylhydroxylamines to 1-Boc-3-(2-nitrovinyl)indoles followed by mild reduction of the adducts. The obtained (indol-3-yl)ethane-1,2-diamines are convenient synthetic precursors for several classes of marine alkaloids. The first total synthesis of racemic topsentin C, a secondary metabolite from Hexadella sp., based on this approach is reported. The initially proposed structure for topsentin C has been revised.