Cycloaddition versus Alkylation Reactions of 2-Vinylindoles with α,β-Unsaturated Carbonyl Compounds Under Gold Catalysis

Synthesis of tetrahydrocarbazoles through a radical cation [4+2] cycloaddition reaction of 2-vinylindoles

A redox umpolung strategy for the synthesis of complex tetrahydrocarbazoles is reported. The reaction involves a visible light promoted radical cation [4+2] cycloaddition between 2-vinylindoles and conjugated alkenes that proceeds with good yields and diastereoselectivity.

Divergent Pd-catalyzed Functionalization of 4-Oxazolin-2-ones and 4-Methylene-2-oxazolidinones and Synthesis of Heterocyclic-Fused Indoles

Palladium-catalyzed functionalization was presently performed on two building blocks: 4-oxazolin-2-ones and 4-methylene-2-oxazolidinones. Direct Heck arylation of 4-oxazolin-2-ones led to a series of 5-aryl-4-oxazolin-2-ones, including analogues with N-chiral auxiliary, in an almost quantitative yield. The Pd(II)-catalyzed homocoupling reaction of 4-oxazolin-2-ones provided novel heterocyclic across-ring dienes. Meanwhile, the intramolecular cross-coupling of N-aryl-4-methylene-2-oxazolidinones furnished a series of oxazolo[3,4-a]indol-3-ones. Further functionalization of 4-methylene-2-oxazolidinones afforded substituted indoles and heterocyclic-fused indoles with aryl, bromo, carbinol, formyl, and vinyl groups. A computational study was carried out to account for the behavior of the formylated derivatives. The currently developed methodology was applied to a new formal total synthesis of ellipticine.

Chemistry of 2-Vinylindoles: Synthesis and Applications

As a class of compounds, 2-vinylindoles have demonstrated a wide range of biological properties. Due to the general interest in these synthons, new divergent protocols of chemical synthesis have been...

Recent approaches to the synthesis of tetrahydrocarbazoles

The tetrahydrocarbazole (THC) motif is ubiquitous in natural products and biologically active compounds.

Synthesis of Cyclohepta[b]indoles by (4 + 3) Cycloaddition of 2-Vinylindoles or 4H-Furo[3,2-b]indoles with Oxyallyl Cations

The synthesis of cyclohepta[b]indole derivatives through the dearomative (4 + 3) cycloaddition reaction of 2-vinylindoles or 4H-furo[3,2-b]indoles with in situ generated oxyallyl cations is reported. Oxyallyl cations are generated from α-bromoketones in the presence of a base and a perfluorinated solvent. Cyclohepta[b]indole scaffolds are obtained under mild reaction conditions, in the absence of expensive catalysts, starting from simple reagents, in good to excellent yields and with complete diasteroselectivity. Preliminary expansion of the scope to 3-vinylindoles and to aza-oxyallyl cations is reported.

Catalytic Asymmetric Synthesis of Chiral 2-Vinylindole Scaffolds by Friedel-Crafts Reaction

A chiral bis(imidazolidine)pyridine (PyBidine)-Ni(OTf)₂ complex smoothly catalyzed an asymmetric Friedel-Crafts reaction of 2-vinylindoles with nitroalkenes to give chiral indoles in a highly enantioselective manner while maintaining the 2-vinyl functionality. The chiral 2-vinylindoles offer unique chiral scaffolds for diverse transformations.

TBAF catalyzed one-pot synthesis of allenyl-indoles

The site selective synthesis of functionalized indoles is presented under environmentally convenient tetrabutylammonium fluoride catalysis.

Breaking aziridines to construct morpholines with a gold(i)-catalyzed tandem ring-opening and cycloisomerization reaction

A convenient synthetic method for the construction of morpholine derivatives from easily available aziridines and propargyl alcohols has been successfully developed. A tandem nucleophilic ring-opening of aziridine/6-exo-dig cyclization/double bond isomerization sequence was achieved by using a single gold(i) catalyst under mild conditions. The gold(i) catalyst served as a π acid and also a σ acid to realize the dual activation of both reactants in this reaction. The obtained unsaturated morpholine products could be easily hydrogenated to achieve target morpholine derivatives with good diastereoselectivities in high yields.

Exploiting the σ-phylic properties of cationic gold(i) catalysts in the ring opening reactions of aziridines with indoles

Gold(i) species catalyze the ring opening reactions of aziridines with indoles as nucleophiles for the synthesis of tryptamines and pyrroloindolines.

Synthesis of constrained analogues of tryptophan

A Lewis acid-catalysed diastereoselective [4 + 2] cycloaddition of vinylindoles and methyl 2-acetamidoacrylate, leading to methyl 3-acetamido-1,2,3,4-tetrahydrocarbazole-3-carboxylate derivatives, is described. Treatment of the obtained cycloadducts under hydrolytic conditions results in the preparation of a small library of compounds bearing the free amino acid function at C-3 and pertaining to the class of constrained tryptophan analogues.

Gold(i)-catalyzed hydroindolylation of allenyl ethers

Nucleophilicity game: the gold(i)-catalyzed reaction/rearrangement of allenyl ethers has been investigated in the presence of indoles. The reaction outcome seems to be decided mainly by the nature of the pendant group of allenyl ether. Control experiments are indicative of an inner sphere mechanism for the hydroindolylation reaction.