1‐Bromo‐2‐(cyclopropylidenemethyl)benzene: A Useful Building Block in the Palladium‐Catalyzed Reaction of 2‐Alkynylbenzenamine

A novel palladium‐catalyzed domino reaction of 1‐bromo‐2‐(cyclopropylidenemethyl)benzene and 2‐alkynylbenzenamine is reported, which generates 2‐(naphthalen‐2‐yl)benzenamines and 5H‐indeno[1,2‐c]quinolines via 6‐endo and 5‐exo cyclization, respectively. The regioselectivity for the final outcome can be affected by phosphine and N‐heterocyclic carbene ligands.     

Asymmetric rhodium-catalyzed hydrogenation meets gold-catalyzed cyclization: Enantioselective synthesis of 8-hydroxytetrahydroisoquinolines

Different furyl-substituted (Z)-dehydroamino acid derivatives were hydrogenated with the rhodium/Mandyphos(OMe)-system to give enantiomeric excesses between 80 and 98 %. The absolute configuration of the newly formed stereogenic center was determined by anomalous diffraction to be R. These chiral furyl alanines were transferred into 8-hydroxytetrahydroisoquinolines by employing gold-catalyzed arene synthesis as the key step. During the latter reaction sequence, also including either a propargylation or a reduction, a protection of the hydroxy group, and a subsequent propargylation, no racemization of the stereogenic center was observed. With very electron-rich furans, instead of the 8-hydroxytetrahydroquinolines as products, furans anellated to seven-membered rings with exocyclic C-C double bonds are formed under the same reaction conditions.     

Heteroacene Synthesis through C−S Cross‐Coupling/5‐endo‐dig Cyclization

Highly efficient, one‐step synthesis of sulfur‐containing heteroacenes was achieved through palladium‐catalyzed C?S cross‐coupling of bis‐alkynes with thioacetate as hydrogen sulfide surrogate. Heteroacenes consisting of three, five, and seven fused aromatic rings were obtained in a single catalytic step by four‐, six‐, and eightfold C?S bond formation.     

Atom-transfer radical addition (ATRA) and cyclization (ATRC) reactions catalyzed by a mixture of [RuCl(2)Cp*(PPh3)] and Magnesium

A new catalytic procedure for atom-transfer radical addition (ATRA) and cyclization (ATRC) reactions is described. The combination of the ruthenium(III) complex [RuCl(2)Cp*(PPh3)] (Cp*: pentamethylcyclopentadienyl) with magnesium allows these reactions to be performed under mild conditions with high efficiency. In most cases, the catalyst concentrations required are significantly lower than those used in previously reported procedures. It is suggested that magnesium acts as a reducing agent that generates and regenerates the catalytically active ruthenium(II) species. The precatalyst [RuCl(2)Cp*(PPh3)] has been analyzed by X-ray crystallography.