(2S)-2-Anilinomethylpyrrolidine: an efficient in situ recyclable chiral catalytic source for the borane-mediated asymmetric reduction of prochiral ketones in refluxing toluene

Metal-free aminoamidiniumation employing N-iodosuccinimide: facile syntheses of bicyclic imidazolidiniums and cyclic vicinal diamines

NIS-mediated aminoamidiniumation has been developed for the syntheses of bicyclic imidazolidinium salts, which could be readily converted into 2-substituted pyrrolidine and indoline diamines.

Biotransformation of α-bromoacetophenones by the marine fungus Aspergillus sydowii

The biotransformation reactions of α-bromoacetophenone (1), p-bromo-α-bromoacetophenone (2), and p-nitro-α-bromoacetophenone (3) by whole cells of the marine fungus Aspergillus sydowii Ce19 have been investigated. Fungal cells that had been grown in artificial sea water medium containing a high concentration of chloride ions (1.20 M) catalysed the biotransformation of 1 to 2-bromo-1-phenylethanol 4 (56%), together with the α-chlorohydrin 7 (9%), 1-phenylethan-1,2-diol 9 (26%), acetophenone 10 (4%) and phenylethanol 11 (5%) identified by GC-MS analysis. In addition, it was observed that the enzymatic reaction was accompanied by the spontaneous debromination of 1 to yield α-chloroacetophenone 5 (9%) and α-hydroxyacetophenone 6 (18%) identified by GC-FID analysis. When 2 and 3 were employed as substrates, various biotransformation products were detected but the formation of halohydrins was not observed. It is concluded that marine fungus A. sydowii Ce19 presents potential for the biotransformations of bromoacetophenone derivatives.

Recent development and improvement for boron hydride-based catalytic asymmetric reduction of unsymmetrical ketones

Catalytic asymmetric reduction of prochiral ketones with hydrides such as boranes and borohydrides is one of the simplest and the most convenient methods for obtaining chiral alcohols. This tutorial review describes the most significant advances recently achieved for enhancing the enantioselectivity and practicability of the reduction using this methodology. The review covers the development of new homogeneous and/or immobilized catalysts for asymmetric reduction using borane or borohydride reagents and practical improvement of the well-known oxazaborolidine (OAB)-catalysed reduction through developing more stable, cost effective and recoverable OABs, scalable and environmental friendly borane sources, and one-pot procedures for the reduction.

Synthesis of a new C(2)-symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones

A new C(2)-symmetric chiral catalyst 3,5-bis[(2S)-(hydroxy-diphenylmethyl)- pyrrolidin-1-ylmethyl]-1,3,4-oxadiazole was successfully synthesized by the reaction of 2,5-dichloromethyl-1,3,4-oxadiazole with (S)-alpha,alpha-diphenyl-2-pyrrolidinemethanol, and applied to the catalytic asymmetric reduction of prochiral ketones with borane. When the catalyst loading was 1 mol %, enantiomeric excesses of up to 86.8% and 94.5% were observed in reduction of aromatic and alpha-halo ketones, respectively.