Transition Metal-Catalyzed Enantioselective Synthesis of Chiral Five- and Six-Membered Benzo O-heterocycles

Enantiomerically enriched five- and six-membered benzo oxygen heterocycles are privileged architectures in functional organic molecules. Over the last several years, many effective methods have been established to access these compounds. However, comprehensive documents cover updated methodologies still in highly demand. In this review, recent transition metal catalyzed transformations lead to chiral five- and six-membered benzo oxygen heterocycles are presented. The mechanism and chirality transfer or control processes are also discussed in details.

Structural Insights into the TES/TFA Reduction of Differently Substituted Benzofurans: Dihydrobenzofurans or Bibenzyls?

Various polysubstituted benzofurans were reduced by using triethylsilane in trifluoracetic acid. 2,3-Dihydrobenzofurans or bibenzyl compounds were obtained in high yields, depending on the nature of the substituents at C2 and on the benzene ring of the core structure. A p-anisole substituent at C2 of benzofurans always led to the corresponding bibenzyls.

Iridium-Catalyzed Enantioselective Hydrogenation of Indole and Benzofuran Derivatives

Enantioselective hydrogenation of a broad spectrum of N-, O-, and S-containing aromatic benzoheterocycles or nonaromatic unsaturated heterocycles has been realized by using an Ir/SpinPHOX (SpinPHOX=spiro[4,4]-1,6-nonadiene-based phosphine-oxazoline) complex as the catalyst, affording an array of the corresponding chiral benzoheterocycles (30 examples) with excellent enantioselectivities (>99 % ee in most cases) and turnover numbers up to 500.

Mild and efficient synthesis of trans-3-aryl-2-nitro-2,3-dihydrobenzofurans on water

A protocol to prepare trans-3-aryl-2-nitro-2,3-dihydrobenzofurans has been developed on water. The protocol avoids the use of toxic solvents, tedious work-up procedures, and chromatographic separation.