Novel intramolecular cyclization of N-alkynyl heterocycles containing proximate nucleophiles

Intramolecular cyclization of 2-acyl-1-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleus.     

Palladium-catalyzed arylation of alpha-methylene-gamma-butyrolactone: 3-benzylfuran-2(5H)-ones vs (Z)-benzylidene-gamma-butyrolactones and their reduction to 3-benzyl-gamma-butyrolactones

[reaction: see text] The palladium-catalyzed arylation of the alpha-methylene-gamma-butyrolactone proceeds in good yields and may be directed toward the synthesis of 3-benzylfuran-2(5H)-ones when the starting aryl iodides contain strongly electron-withdrawing groups. The combined palladium-catalyzed arylation/hydrogenation of the alpha-methylene-gamma-butyrolactone represents a new simple entry into functionalized alpha-benzyl-gamma-butyrolactones.     

Gold-catalyzed reactions of 2-alkynyl-phenylamines with alpha,beta-enones

[reaction: see text] The gold-catalyzed reaction of 2-alkynyl-phenylamines with alpha,beta-enones represents a new general one-pot entry into C-3-alkyl-indoles by sequential reactions. Gold-catalyzed sequential cyclization/alkylation, N-alkylation/cyclization, or N-alkylation/cyclization/alkylation reactions leading to different indoles can be directed by changing the 2-alkynyl-phenylamine 1/alpha,beta-enone 3 ratio and the reaction temperature. Unusual gold-catalyzed rearrangement reaction of indoles are observed at 140 degrees C. New gold-catalyzed formation of propargyl-alkyl ether under mild conditions and the hydration reaction of N-acetyl-2-ethynyl-phenylamine are reported.     

Electrophilic cyclization of o-acetoxy- and o-benzyloxyalkynylpyridines: an easy entry into 2,3-disubstituted furopyridines

[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.     

Pd-catalyzed regioselective hydroarylation of α-(2-aminoaryl)-α,β-ynones with organoboron derivatives as a tool for the synthesis of quinolines: experimental evidence and quantum-chemical calculations

The Pd-catalyzed hydroarylation of β-(2-aminoaryl)-α,β-ynones with organoboron derivatives, leading to 2,4-diarylquinolines in good to excellent yields through sequential cycloamination, has been investigated. The reaction is catalyzed by both Pd(II) and Pd(0) precatalysts, and can be carried out even under neutral conditions. The regiochemical outcome is inverted with respect to the Pd-catalyzed hydroarylation of β-(2-aminoaryl)-α,β-ynones with aryl iodides. This aspect has been rationalized using quantum-chemical calculations, which show significant differences between the energy barriers of the regioisomeric transition states for the migratory insertion (hydropalladation) step, and are consistent with the charge density of the π complex that undergoes such insertion.