Functionalized Bipyrroles and Pyrrolyl-Aminopyrones from Acylethynylpyrroles and Diethyl Aminomalonate

An efficient method for the synthesis of 1H,1′H-2,3′-bi­pyrroles (up to 72% yield) by the cyclocondensation of easily available 2-(acylethynyl)pyrroles with diethyl aminomalonate hydrochloride has been developed. The reaction proceeds under reflux in MeCN (6 h) in the presence of Cs2CO3. Under the same conditions, 2-(acylethynyl)pyrroles with bulky (benzyl and octyl) substituents at nitrogen atom react with diethyl aminomalonate to afford 1H,2′H-2,3′-bipyrroles and pyrrolyl-aminopyrones.

One-pot synthesis of 3-aminofurans using a simple and efficient recyclable CuI/[bmim]PF6 system

A one-pot three-component reaction of several 2-ketoaldehydes, secondary amines and terminal alkynes to access 3-aminofurans proceeded well in [bmim][PF₆] using a simple and cheap CuI catalyst. The resultant 3-aminofuran products were easily isolated using diethyl ether and the CuI/[bmim][PF₆] system was reused six times with a slight decrease in the activity.

2-(Dimethylamino)phosphinine: A Phosphorus-Containing Aniline Derivative

The yet unknown 2-amino-substituted λ³ ,σ² -phosphinines are phosphorus-containing aniline derivatives. Calculations show that the strong interaction of the π-donating NR₂  group with the aromatic system results in a high π-density at the phosphorus atom. We could now synthesize 2-N(CH₃ )₂ -functionalized phosphinines, starting from a 3-N(CH₃ )₂ -substituted 2-pyrone and (CH₃ )₃ Si-C≡P. Their reaction with CuBr⋅S(CH₃ )₂ affords Cu^I  complexes with the first example of a neutral phosphinine acting as a rare bridging μ₂ -P-4e donor-ligand between two Cu^I  centers. Our experimental and theoretical investigations show that 2-aminophosphinines are missing links in the series of known 2-donor-functionalized phosphinines.

Regioselective Formation of Substituted Indoles: Formal Synthesis of Lysergic Acid

A Diels-Alder reaction-based strategy for the synthesis of indoles and related heterocycles is reported. An intramolecular cycloaddition of alkyne-tethered 3-aminopyrones gives 4-substituted indolines in good yield and with complete regioselectivity. Additional substitution is readily tolerated in the transformation, allowing synthesis of complex and non-canonical substitution patterns. Oxidative conditions give the corresponding indoles. The strategy also allows the synthesis of carbazoles. The method was showcased in a formal synthesis of lysergic acid.

Synthesis of 1,6-Dihydropyridine-3-carbonitrile Derivatives via Lewis Acid-Catalyzed Annulation of Propargylic Alcohols with (E)-3-Amino-3-phenylacrylonitriles

A novel Lewis acid-catalyzed, highly efficient, practical, and atom-economical protocol for the synthesis of functionalized 1,2-dihydropyridine-3-carbonitrile derivatives in the presence of Bi(OTf)₃ (10 mol %) in tetrahydrofuran (2.0 mL) at 80 °C for 8 h in air is described, starting from readily accessed propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles. This cycloaddition protocol, which is scalable and proceeds under mild conditions, is amenable to the gram-scale construction of valuable 1,2-dihydropyridine-3-carbonitriles. Furthermore, the good functional group compatibility and broad scope of this strategy were demonstrated by a broad range of propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles, with yields ranging from 34 to 96%.

Tandem N, N-Dialkylation Reaction of N-Trimethylsilyl α-Iminoesters Utilizing an Umpolung Reaction and Characteristics of the Silyl Substituent: Synthesis of Pyrrolidine, Piperidine, and Iminodiacetate

Umpolung reactions of N-trimethylsilyl α-iminoester with organometallics gave directly N-alkylaminoesters in high yields without the need for removing a protecting group at the nitrogen atom. Efficient syntheses of pyrrolidines, piperidines, and iminodiacetate derivatives were also developed via tandem N,N- or N, C-dialkylation reactions utilizing characteristics of the silyl substituent. Furthermore, under the influence of silica gel, the addition of an enolate to the imino nitrogen proceeded to give an iminodiacetate derivative.

Synthesis of 4-styrylcoumarins via FeCl3-promoted cascade reactions of propargylamines with β-keto esters

A versatile and highly regioselective FeCl₃-promoted tandem cyclization reaction of in situ generated alkynyl o-quinone methides (o-AQMs) with β-keto esters has been developed.

Copper-catalyzed tandem A3-coupling–isomerization–hydrolysis reactions of aldehydes and terminal alkynes leading to chalcones

A³ coupling is not the end: catalyzed by a simple copper salt, the reaction of aldehyde, alkyne, and amine can afford chalcone.